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                        MOTOR-CAR PRINCIPLES




                        MOTOR-CAR PRINCIPLES

                      _THE GASOLINE AUTOMOBILE_

                                 BY

                          ROGER B. WHITMAN

                             ILLUSTRATED

                     [Illustration: Decoration]

                      NEW AND ENLARGED EDITION

            D. APPLETON AND COMPANY NEW YORK, LONDON MCMX




                       COPYRIGHT, 1907, 1909,
                     BY D. APPLETON AND COMPANY




                            INTRODUCTION


The development of the gasoline automobile at home and abroad has
produced a great variety of designs, good, bad, and indifferent, but
the advancement of the industry has weeded out the unsatisfactory and
improved the good until with few exceptions the leading makes show
a striking similarity in all but details. The advantages of certain
forms of construction have been recognized, and their adoption by the
large majority of makers has produced what may be called a standard
type.

The object of this book is to explain the principles that underlie
automobile construction and operation, and to illustrate the
movements and mechanical combinations adopted in present-day
practice. It is not the intention to explain the exact details of
construction of the different cars, and the illustrations have
been prepared with the sole object of making the principles clear,
for with an understanding of these there should be no difficulty in
comprehending any particular application of them.

The lubrication table on pages 244 and 245, which was prepared by Mr.
T. D. Hanauer, is reproduced through the courtesy of the _Scientific
American_.

       *       *       *       *       *

The advantages of magneto ignition for internal combustion engines
are so obvious that designers and inventors have directed their
attention to the perfection of apparatus that will improve present
methods. The number of systems proposed for the purpose is very
large in comparison with the number in actual and practical use,
and as in a work of this size it would be impossible to describe
the many methods for the application of the magneto that are on the
market, attention has been given only to those that are in actual,
everyday use. The absence of a practical treatise on the principles,
application, and care of low and high tension magnetos is the reason
for the addition of the appendix to this work.

R. B. W.




                              CONTENTS


                              CHAPTER I

                     GASOLINE-ENGINE PRINCIPLES

                                                                  PAGES

  Properties of gases—Steam-engine principles—Gasoline-engine
  principles—Combustion and explosion—Events of cycle—Four-cycle
  and two-cycle engines—Strokes of cycle—Fly wheel—Valves—Inlet
  stroke—Inlet valve closing—Compression-combustion stroke—Advantages
  of compression—Instant of ignition—Advancing and retarding
  ignition—Limit of compression—Power stroke—Heat losses—Opening of
  exhaust valve—Exhaust stroke—Clearance—Back pressure—Steam and
  Gasoline engines compared—Gasoline—engine power                  1-19


                               CHAPTER II

                              ENGINE PARTS

  Crank shaft—Crank-shaft bearings—Relative position
  of cranks—Connecting rod—Wrist pin—Piston and piston
  rings—Automatically and mechanically operated valves—Cams
  and cam shaft—Secondary shaft—Two-to-one gears—Valve-lifter
  rod—Valve locations—Muffler—Engine cooling—Cooling by
  Water—Pumps—Radiators—Pressure and gravity systems—Cooling by
  air—Lubrication                                                 20-36


                               CHAPTER III

                             ENGINE BALANCE

  Vibrations of engine—One-cylinder engine—Horizontal
  double-opposed—Two-cylinder vertical—Four-cylinder—Firing
  order—Balance of three- and six-cylinder engines—Comparison of engine
  types                                                           37-46


                               CHAPTER IV

                            TWO-CYCLE ENGINES

  Principle—Construction—Ports—Cycle—Action—Advantages and
  disadvantages                                                   47-51


                                CHAPTER V

                     CARBURETION AND GASOLINE FEEDS

  Carburetion—Carburetor—Carburetor parts—Carburetor action—Necessity
  for auxiliary air—Auxiliary air inlet—Automatic and mechanically
  controlled air inlet—Carburetors with side and central
  mixing chambers—Mechanically controlled carburetor—Surface
  carburetors—Gravity feed—Pressure feed—Check and relief valve   52-73


                               CHAPTER VI

                                IGNITION

  Ignition system—Electric current—Parts of ignition system—Flow
  of current—Conductors and insulators—Resistance—Measurements of
  current—Lead and return wires—Grounding the return—Generators—Dry
  cell—Storage cell—Electrolyte—Hydrometer—Battery connections:
  series, parallel and multiple—Magnetism—Magnets—Magnetic
  lines of force—Magnetic field—Field and armature—Magneto and
  dynamo—Switch—Switch parts                                      74-90


                               CHAPTER VII

                         IGNITION—(_Continued_)

  Ignition systems—Make-and-break
  system—Igniter—Tappet—Connections—Primary induction coil—Action of
  coil—Induced current—Magneto—Jump-spark system—Secondary induction
  coil—Primary and secondary circuits—Timers—Mechanical and magnetic
  vibrators—Spark plug—Circuit—Condenser—Secondary distributer   91-111


                              CHAPTER VIII

                              TRANSMISSION

  Transmission parts—Clutches—Friction-cone clutch—Reversed
  friction-cone clutch—Multiple disk clutch—Internal expanding
  clutch—Change-speed mechanisms—Sliding gear: progressive and
  selective types—Use of clutch in changing gear                112-131


                               CHAPTER IX

                       TRANSMISSION—(_Continued_)

  Planetary type of change-speed mechanism—Individual clutch—Friction
  type—Final drive—Turning the direction of the power—Bevel
  gears—Single-chain drive—Propeller-shaft drive—Universal
  joints—Live axle—Floating axle—Torsion rod—Double-chain
  drive—Jack shaft—Differential—Bevel-gear differential—Spur-gear
  differential—Driving-gear ratios                              132-160


                                CHAPTER X

                              RUNNING GEAR

  Steering—Front axle—Steering knuckles and arms—Drag link—Steering
  principles—Steering mechanisms—Brakes: contracting and
  expanding—Brakes: single- and double-acting—Running brake—Emergency
  brake—Engine as a brake—Brake equalizer—Tires—Tire construction—Tire
  inflation—Skidding—Antiskid devices—Springs—Shock absorbers—Distance
  rods                                                          161-178


                               CHAPTER XI

                                TROUBLES

  Ignition—Circuit—Battery—Magneto—Coil—Spark
  plug—Igniter—Timer—Secondary
  distributer—Switch—Gasoline—Tank—Carburetor—Compression—
  Cooling—Freezing—Lubrication
                                                                179-202


                               CHAPTER XII

                            LOCATING TROUBLE

  Make-and-break ignition—Jump-spark ignition—Carburetor—Engine will
  not start—Engine will not deliver full power—Weak explosions—Missing
  explosions—Missing at high speed—Engine starts well, but comes to a
  stop—Overheating—Engine comes to a stop—Noises                203-219


                              CHAPTER XIII

                      MAINTENANCE AND CONSTRUCTION

  Inspection—Washing the car—Tires—Care of the engine—Care of the
  chains—Valve grinding—Care of the steering mechanism—Care of the
  springs—Adjusting the vibrators—Matching coils—Adjusting the
  carburetor—Setting the valves—Ignition wiring                 220-242

  LUBRICATION TABLE                                             244-245


                                APPENDIX

  Magnetism—Induction—Magneto principles—General magneto troubles—Low
  tension ignition system—Setting up, care and troubles—Low tension
  magneto with secondary coil—Direct high tension magneto—Bosch
  two-spark magneto—Bosch four-spark magneto—Dual systems—Magnetic plug
  ignition—Inductor magnetos                                    247-326

  TESTING CHART _Between_                                   326 and 327

  INDEX                                                         327-339




                        LIST OF ILLUSTRATIONS


  FIG.                                                             PAGE

   1. Engine Actions                                                  3

   2. Gasoline Engine Cycle                                           7

   3. Gasoline Engine in Section                                     21

   4. Crank Shafts                                                   22

   5. One-Throw Crank Shaft                                          23

   6. Connecting Rod                                                 23

   7. Piston and Piston in Section                                   24

   8. Piston Rings                                                   24

   9. Conical Valve Seat                                             25

  10. Automatic Inlet Valve in Cage                                  25

  11. Cam Action                                                     27

  12. Four Arrangements of Valves                                    29

  13. Circulation of Cooling Water                                   31

  14. Types of Pumps                                                 32

  15. Radiator Constructions                                         33

  16. Radiator and Fan                                               33

  17. Engine Arrangements Showing Order of Firing                    40

  18. Two-Cycle Engine                                               48

  19. Carburetor Principles                                          54

  20. Automatic Carburetors                                          59

  21. Mechanically Controlled Carburetor                             63

  22. Float-Feed Carburetor with Gravity Gasoline Feed               65

  23. Pressure-Feed Gasoline System                                  67

  23A. Types of Float Valves                                         69

  23B. Types of Auxiliary Air Inlets                                 71

  24. Battery Connections                                            85

  25. Make-and-Break Ignition                                        92

  26. Types of Timers                                                99

  27. Mechanical Vibrator                                           104

  28. Magnetic Vibrator                                             104

  29. Spark Plug and Spark Plug in Section                          107

  30. Ignition Circuit                                              108

  31. Friction Cone Clutches                                        115

  32. Multiple-Disk Clutch                                          117

  33. Sliding Gear—Progressive Type                                 122

  34. Selective Type                                                127

  35. Planetary Type                                                133

  36. Individual Clutch and Friction Drive                          139

  37. Propeller and Single-Chain Drives                             143

  38. Typical Universal Joint                                       144

  38A. Types of Shaft Drives                                        145

  39. Live Axle—Non-floating Type                                   147

  40. Live Axle—Floating Type                                       147

  40A. Dead Axle with Driving Shaft                                 149

  41. Torsion Rod                                                   150

  42. Double Side-Chain Drive                                       151

  43. Differentials                                                 154

  44. Two Arrangements of the Drag Link                             162

  45. Steering Principles                                           163

  46. Steering Mechanisms                                           165

  47. Three Varieties of Brakes                                     168

  48. Springs                                                       175

  49. Distance or Radius Rods                                       177

  50. Jump-Spark Wiring Diagrams                                    237

  51. Jump-Spark Wiring Diagrams                                    239

  52. Make-and-Break Wiring Diagram                                 241

  53. Make-and-Break Wiring Diagram                                 241


                      ILLUSTRATIONS IN APPENDIX

  1. Magnetic Lines of Force                                        250

  2. Armature                                                       256

  3. The Armature and Lines of Force                                256

  4. The Armature and Lines of Force                                257

  5. The Armature and Lines of Force                                257

  6. The Armature and Lines of Force                                258

  7. The Armature and Lines of Force                                259

  8. Make-and-Break System                                          271

  9. Eisemann Ignition System                                       285

  10. Wiring Diagram, H.-T. Magneto Interchangeable with
        Secondary Coil                                              298

  11. Wiring Diagram, Two-Spark Magneto                             302

  12. Timing Diagram, Two-Spark Magneto                             304

  13. Diagrams showing Position of Shield Revolving about Armature  309

  14. Wiring Diagram, Four-Spark Magneto                            312

  15. Timing Diagram, Four-Spark Magneto                            314

  16. Bosch Jump-Spark Dual System                                  318

  17. Remy Inductor                                                 321

  18. Inductor Giving Six Waves                                     321

  19. Magnetic Igniter                                              324

  20. Wiring Diagram of Magnetic Igniter System                     324




                        MOTOR-CAR PRINCIPLES




                              CHAPTER I

                     GASOLINE ENGINE PRINCIPLES


The action of a steam, gasoline, or hot-air engine depends on the
principle that when air or other gas is heated it expands, and that
if it is confined in a space that will not permit it to expand,
in striving to do so it creates pressure against all parts of the
chamber in which it is contained. The more a gas is heated, the more
it will expand if it is free to do so, and if not free, the greater
will be the pressure that it will exert in striving to expand.
Pressure may thus be generated by heat, and following along similar
lines, heat may be produced by pressure, for when the pressure of
a gas is increased by compressing it, or forcing it to occupy a
smaller space, the gas will become heated. The reverse is also true,
that when a gas is cooled, its volume is reduced, which reduces
the pressure that it exerts; similarly, reducing the pressure by
permitting the gas to expand reduces its temperature.

To state these principles in another form, to create pressure in a
gas it must either be heated or compressed into a smaller space,
and to reduce its pressure it must either be cooled or permitted to
expand.

The action of a locomotive, the most familiar type of steam engine,
is no mystery, and the production of steam in the boiler, its passage
to the cylinder, and the application of its steady pressure against
first one side of the piston and then the other, resulting in the
turning of the driving wheels, are well understood. Water being
converted into steam in the boiler, pressure is created because of
the tendency of the steam to expand, but the only place in which it
may expand is the cylinder, where in so doing it moves the piston.

[Illustration: FIG. 1.—ENGINE ACTIONS.]

A gasoline engine is similar to a steam engine in that its piston is
moved by the pressure exerted by a heated and expanding gas; it is
different in that the pressure is produced inside of the cylinder
by the combustion of an inflammable mixture of gasoline vapor,
instead of being generated in a boiler away from the cylinder. The
heat of the combustion creates great pressure, and as the piston is
the only part that can give before it, it is moved from one end of
the cylinder to the other, this motion being utilized in the turning
of the crank shaft. The combustion, which is so rapid that the
generally accepted term for it is explosion, can occur only after the
mixture has been drawn into the cylinder, and so prepared that it
ignites quickly and burns completely, with the object of obtaining
the greatest possible heat from it in the shortest possible time. In
order that one explosion may be followed by another, the burned and
useless products of combustion must be expelled to make place for a
fresh charge of the inflammable mixture.

These successive events, forming a =cycle=, must be performed as
long as the engine runs, and the constantly changing pressure in the
cylinder due to the movement of the piston allows a fresh charge to
enter, prepares it, and expels the products of combustion after the
pressure that they have exerted has been utilized.

While in the great majority of steam engines the steam acts first
on one side of the piston and then on the other, in an automobile
gasoline engine the pressure is exerted on only one side, the
combustion of the mixture taking place between the piston and the
closed end, or =head=, of the cylinder. The other end of the cylinder
is open, and the piston slides between the ends, its movement from
one end to the other, called a =stroke=, corresponding to a half
revolution of the crank shaft.

Gasoline engines are divided into two classes, according to the
number of strokes of the piston that are necessary to accomplish the
cycle; in the most usual type, four strokes are necessary, the class
being called the four-stroke-cycle, or =four-cycle=, in distinction
to the two-stroke-cycle, or =two-cycle=, in which but two strokes are
necessary.

Of the five events that compose the cycle, three (the =inlet=, during
which the fresh mixture enters the cylinder, its =compression= or
preparation, and the =exhaust= of the burned gases) are performed
by the piston; during the =power= event the piston is moved by the
pressure resulting from the combustion, while the =combustion= event
is due to an outside source. In the four-cycle type of engine,
which is in almost universal use for automobiles, the events are
considered with reference to the movement made by the piston
during which they are performed, and may be called the =inlet=,
=compression-combustion=, =power=, and =exhaust strokes=. In order
that the engine may continue to run, it is obvious that the events
must be performed in the correct order, and that the failure of one
will affect all the others.

During the inlet stroke, a charge of fresh mixture enters the
cylinder as the piston makes an outward stroke from the closed
toward the open end. When the piston makes the following inward
stroke, the mixture is compressed and combustion occurs, the pressure
from which drives the piston outward on the power stroke. This is
followed by another inward stroke, which pushes the burned gases
out of the cylinder. It will be seen that power is developed during
only one stroke of the four, the other three being required in
the preparation for the following power stroke. The movement of the
piston over these three dead strokes is secured by attaching to the
crank shaft a heavy =fly wheel=, the momentum of which, acquired
during the power stroke, keeps the crank shaft revolving and the
piston in motion while the events are performed.

[Illustration: _SUCTION STROKE_ _COMPRESSION STROKE_

_POWER STROKE_ _EXHAUST STROKE_ FIG. 2.—GASOLINE ENGINE CYCLE.]

The space between the piston and cylinder head in which the
combustion occurs is called the =combustion space=, and the =inlet=
and =exhaust valves= open into it, the first being that by which the
fresh mixture enters, and the second that by which the products of
combustion escape. The device for igniting the mixture projects into
the combustion space, and the means of ignition in universal use for
automobile engines is an electric spark.


                            INLET STROKE

During the stroke (Fig. 2), the piston is moved outward by the crank
shaft, which is revolved either by hand or by the momentum of the
fly wheel. This movement increases the size of the combustion space,
thereby reducing the pressure in it, and the higher pressure of the
atmosphere outside of the cylinder will force fresh mixture into the
combustion space, the inlet valve being open to admit it. If the
piston moves slowly, the mixture will be able to enter fast enough to
keep the pressure in the combustion space equal to that outside, but
at the high speed at which a gasoline engine is run the piston will
reach the end of its stroke before a complete charge has had time to
enter, so that the pressure in the combustion space will still be
below that of the atmosphere. If the inlet valve closed at this point
so that no more mixture could enter, the combustion of the partial
charge would result in a lower pressure than would be possible with
a full charge; the inlet valve should therefore remain open until
the piston reaches the point of its next inward stroke at which the
pressure in the cylinder equals that outside.


                    COMPRESSION-COMBUSTION STROKE

The compression and the combustion of the charge occur during the
next inward stroke of the piston.

The period between the bringing together of the liquid gasoline and
air and its admission to the cylinder is too brief to secure perfect
combination, and the mixture that results is not satisfactory. A
portion of the air will not have been able to come into contact with
the gasoline, and much of the liquid will not have been vaporized;
what passes into the cylinder consists of pure air, liquid gasoline,
and a more or less perfect mixture of the two. The combustion of this
would be slow and incomplete, resulting in loss of power and waste of
fuel. In order to render the mixture more perfect, advantage is taken
of the heat that is produced by compression; the inward stroke of
the piston raises the temperature of the mixture by compressing it,
the heat rendering the gasoline more volatile, and the compression
forcing it into combination with the air. Even this does not result
in the formation of a perfect mixture, for the period is too short to
effect it. The failure of an engine to deliver full power may often
be traced to this condition, for the air and gasoline vapor, instead
of being thoroughly combined and mixed, will be in layers, so to
speak, and the combustion will be slow and uneven. Future development
of the internal combustion engine will no doubt eradicate this, to
the increase of efficiency and economy.

The charge of inflammable mixture can produce a certain amount of
heat, and the more rapidly and completely this heat is obtained, the
greater and more sudden will be the rise in pressure. The pressure
will be greater when the mixture is contained in a small space than
when in a large, and as the combustion space is smallest when the
piston is at its inmost point, the greatest pressure will be obtained
if combustion is complete at this point. If the combustion of the
mixture were instantaneous, it should be ignited at this point; but
even though very rapid, it nevertheless burns slowly enough to make
it necessary to ignite it sufficiently before the end of the stroke
to have the combustion complete as the piston comes into position
to move outward. The instant at which the mixture must be ignited
in order to produce this result depends on the speed of the piston,
for the interval between the ignition of a good mixture and its
complete combustion does not vary to any great extent. When the
piston is moving slowly, the mixture may be ignited toward the end
of the compression stroke, for there will be sufficient time for
complete combustion by the time the stroke is ended; but when moving
at high speed, ignition must occur much earlier in the stroke, as
otherwise the piston will have completed the compression stroke and
begun to move outward on the power stroke before the mixture is
entirely burned. The instant at which ignition occurs also depends
on the mixture that is used, for its quality and proper combination
make a difference in the rapidity with which it burns. The better the
quality of the mixture, the faster and more completely it will burn,
and ignition may occur later in the stroke than would be possible
with a mixture of poor quality. As the mixture is ignited by the
passing of an electric spark in the combustion space, the difference
in the instant at which it occurs may be secured by permitting the
spark to pass earlier or later, and this is under the control of the
driver.

When ignition occurs early in the compression stroke, the spark is
said to be =advanced=, in distinction to a =retarded= spark, which
passes when the compression stroke is more nearly complete.

If the spark is advanced too much, combustion will be complete before
the piston has reached the end of the compression stroke, and it
will be necessary to force it to the end of the stroke against the
pressure by the momentum of the fly wheel, in order that it may get
into position to move outward on the power stroke. In such a case,
the momentum may not be sufficient to overcome the pressure, and
the piston will be brought to a stop. A retarded spark results in
the combustion of the mixture being completed after the piston has
begun to move outward on the power stroke, and the pressure will
then be reduced because it is exerted in a larger space, the piston
consequently being moved with less force; if the spark is still
further retarded, the combustion will not be complete by the time the
exhaust begins, and the heat from only a portion of the mixture will
be utilized, because it will still be burning as it is forced out of
the cylinder.

The position at which the spark occurs is one of the means by which
the speed of the engine is controlled, for the low pressure that
results from a retarded spark moves the piston at low speed, while
the greater pressure from an advanced spark drives the piston outward
with more force and higher velocity.

While high compression of the charge improves its quality, and
results in combustion being more rapid and complete, it has limits,
and if carried too far the heat generated by the compression will be
sufficient to ignite the mixture. This would have a bad effect on
the operation of the engine, for the pressure would then be produced
at the wrong point of the stroke, retarding instead of assisting the
revolution of the crank shaft. Modern practice has shown that in
engines that are maintained at a proper temperature the best results
are obtained by compressing the mixture to from sixty to eighty
pounds to the square inch; there are instances in which a higher
compression is obtained, but the liability to ignite the mixture
prematurely makes it undesirable.


                            POWER STROKE

The increasing size of the combustion chamber as the piston moves
outward on the power stroke permits the gases to expand, and in doing
so the temperature will fall, the pressure decreasing in consequence.
A further decrease in pressure is caused by the hot gases being in
contact with the metal cylinder and piston, which absorb heat. The
more slowly the engine runs, the longer the gases will be in contact
with the cylinder walls, and the more opportunity there will be for
loss of heat from this cause; at higher speeds, there will be less
time for heat to be absorbed by the cylinder walls, and more will be
utilized in expanding the gases and producing work.

Even at the outmost position of the piston, the combustion space
will not be large enough to permit the gases to expand until their
pressure has dropped to that of the atmosphere, so that they will
still be exerting pressure. By opening the exhaust valve, the gases
will have an outlet for expansion, and will begin to rush out. While
the pressure might be utilized against the piston to the end of the
power stroke, it has been found that better results are obtained by
opening the exhaust valve before the piston reaches the end of the
power stroke. There is then a higher pressure forcing the gases out
than there would be later in the stroke, and the greater quantity
of gases that escapes leaves less to be expelled during the exhaust
stroke.


                           EXHAUST STROKE

The inward movement of the piston pushes out of the open exhaust
valve the gases that have not escaped through their desire to expand.
The exhaust valve remains open for the entire stroke, but when the
engine is running at high speed the piston moves so rapidly that
the gases cannot escape fast enough to prevent their being slightly
compressed. When the piston is at its inmost point, the gases are
still flowing through the valve because of this slight compression,
and if the valve closed, a portion would be retained. The best
results come from the closing of the exhaust valve not at the end
of the exhaust stroke, but a short time after the piston has begun
to move outward again, during which period the compression forces
the gases out. The exhaust valve closes at the point when the slight
compression has been reduced to the pressure of the atmosphere by the
escape of the gases and the enlargement of the combustion space.

If the piston completely filled the combustion space when at its
inmost point, all of the burned gases would be expelled, but the
necessity for leaving a space in which combustion may take place
renders this impossible, and a small portion of the burned gases
therefore remains in the cylinder. The space between the cylinder
head and the piston when at its inmost point, called the =clearance=,
should be as small as possible, in order that the amount of these
gases remaining in the cylinder may not be sufficient to contaminate
the fresh charge and weaken the pressure of its combustion.

The passages through which the burned gases are led away from the
cylinder must be large and free from obstructions, for if a free
flow is not permitted back pressure will be set up, which will
prevent the largest possible amount of gases from escaping, and leave
a greater portion to contaminate the fresh charge.

The power that a gasoline engine is capable of developing depends
on the size of the cylinder, the pressure acting on the piston, and
the speed at which it operates. A steam engine, which obtains its
pressure from a boiler, can do work as soon as the steam is turned
into the cylinder, but a gasoline engine must be running before it
can be called on to deliver power. Because of the cycle of events on
which its operation depends, the piston must be forced to perform the
inlet and compression strokes before pressure can be developed, and
it is necessary to revolve the crank shaft by outside means until a
charge of mixture has been taken into the cylinder, compressed, and
ignited, when the engine begins to work by the pressure from the
combustion, and takes up its cycle. Not until this has been done can
it be called on to do work.

A steam engine can be made to deliver more power than it is built
for by increasing the pressure acting against its piston, and the
full pressure of the boiler can be utilized when extra work is
necessary. The power developed by a gasoline engine being greatly
dependent on its speed, and there being no reserve by which greater
power can be developed in emergencies, it is necessary for an engine
of this type to be perfectly adapted to the work that is desired of
it. At excessive speeds the piston acquires great momentum, which
must be overcome at each end of a stroke by the crank shaft, and
while a speed above normal may be attained, it results in the quick
destruction of the bearings and the severe straining of the engine.
The best results in efficiency and long life accompany the running of
the engine at the slowest speed possible for the development of the
required power.




                             CHAPTER II

                            ENGINE PARTS


The sudden and powerful outward movements of the piston under the
pressure from the combustion are transmitted to a =crank shaft=,
which must be of great strength in order to resist the heavy strains
under which it operates. It is made of the best steel available for
the purpose, and has as many =cranks= as the engine has cylinders.
The cranks are generally made in one piece with the shaft for the
sake of strength, and for stiffness there are as many =bearings= as
possible. The number of bearings for the crank shaft of an engine
with four or more cylinders depends on the arrangement of the
cylinders. If the cylinders are evenly spaced, there will be room for
a bearing between each pair of cranks, so that a four-cylinder engine
will have five bearings, one at each end, the other three being
between the cranks. If the cylinders are in pairs, there will not be
room between the cranks of a pair for a bearing, the only space for
it being between the pairs; a four-cylinder engine built in this way
will thus have but three bearings, one at each end and one in the
center. Crank shafts are described by their bearings as three, five,
etc., =point= crank shafts.

[Illustration: FIG. 3.—GASOLINE ENGINE IN SECTION.]

[Illustration: FIG. 4.—_A_, Two-throw crank shaft; _B_, four-throw
crank shaft, 180°.]

The relative positions of the cranks of a crank shaft are expressed
in degrees of a circle; if, for instance, the cranks project from
opposite sides of the shaft so that they are a half revolution apart,
it is called a 180-degree crank shaft.

The outer ends of the crank arms, which correspond to the cranks of a
bicycle, support the =crank pin=, which may be likened to the pedal,
and to this the large end of the =connecting rod= is attached, the
small end being connected to the piston. The connecting rod must be
of great strength, tough but not brittle, and is made of steel or
bronze.

[Illustration: FIG. 5.—ONE-THROW CRANK SHAFT.]

[Illustration: FIG. 6.—CONNECTING ROD.]

The piston is a trifle smaller than the bore of the cylinder, and
its length is usually greater than its diameter. It is hollow, with
one end closed, the closed end being that against which the pressure
is exerted. A =wrist pin= passes through it, and through the small
end of the connecting rod, to enable the latter to swing from side
to side in following the turning of the crank shaft. A tight joint
is maintained between it and the cylinder walls by cast-iron =piston
rings=, which are of square or rectangular cross-section, split so
that they may spring open, and fitted into grooves cut around the
piston. They are of such shape that their tendency to expand keeps
them pressed against the cylinder walls, but being split, their
elasticity prevents their binding; they fit the grooves snugly, and
while they may move freely in them, they hold the pressure from
escaping. The number of rings varies with the design of the engine,
but the most usual arrangement is three to a piston, placed around
the upper end.

[Illustration: FIG. 7.—_A_, Piston; _B_, piston in section.]

[Illustration: FIG. 8.—PISTON RINGS.]

The cylinder should be of the highest grade of cast iron, with the
smoothest possible surface for the piston to slide against.

[Illustration: FIG. 9.—CONICAL VALVE SEAT.]

[Illustration: FIG. 10.—AUTOMATIC INLET VALVE IN CAGE.]

The =valve= openings, or =seats=, are circular, and are usually made
slightly funnel shaped, the =disks= that cover them being slightly
conical to fit. The large end of the funnel is toward the combustion
space, so that when the disk is lifted from its seat it moves inward.
Valves are held against their seats by coil springs that surround
the valve =stems=, which are rods extending from the center of the
disks, and there are two methods by which they are opened. In an
=automatic valve=, the spring that holds the disk against its seat
is weak, and the higher pressure outside of the cylinder during
the suction stroke forces the disk away from its seat against the
pressure of the spring. The valve remains open until the pressure
in the combustion space is about equal to that outside, when the
spring draws the disk back to its seat, to which it is held as long
as the pressure inside is higher than that of the atmosphere. This
arrangement is only possible for inlet valves, and is largely used,
but exhaust valves, and often inlet valves as well, are =mechanically
operated=; that is, they are opened and held open by a mechanism
driven by the crank shaft, in the form of a =cam=. A cam can best be
described as a “wheel with a hump on it,” or, in other words, it is
a piece of metal mounted on a shaft, cylindrical in form except for
one portion, which projects farther from the shaft than the rest. The
cam revolves with the shaft, and the projection, called the =nose=,
will displace anything resting against it. The illustration shows a
cam in three positions of its revolution, with the end of a valve
stem resting against it—the roller being attached to the stem to
reduce the friction. The valve stem is held in =guides=, so that the
only movement it may have is up and down; when the cam revolves, the
nose lifts the stem and opens the valve, holds it open as long as the
flat end of the cam is under the stem, and when the nose passes from
under, the valve is drawn to its seat by the spring.

[Illustration: FIG. 11.—CAM ACTION.]

The moment at which an automatic valve opens is governed partly by
the tension of its spring; if it is too strong, greater pressure will
be required to open it, and it will close sooner than if the tension
is light. Accurate adjustment of this spring is necessary in order
that the charge may enter the combustion space without delay, and
continue to enter as long as possible. The opening and closing of
mechanically operated valves depend on the shape of the cam, and not
being affected by the more or less uncertain action of a spring, they
are more positive in action.

The =cam shaft= on which the cam is mounted is driven by the crank
shaft, but as the valve opens but once during two revolutions, the
cam shaft revolves at half speed, making one revolution while the
crank shaft makes two. This is done by means of =gears=.

If two gears running together, or in mesh, have the same number of
teeth, they will make the same number of revolutions, but if one has
twice as many teeth as the other, the smaller will revolve twice
while the larger revolves once. As the cam shaft must revolve but
once while the crank shaft revolves twice, its gear must have twice
the number of teeth as the gear on the crank shaft. The cam shaft is
also called the =secondary=, or =half-time shaft=, and the gears that
drive it the =two-to-one gears=.

In some designs of engines, the nose of the cam bears directly
against the valve stem, but it is more usual to place a =valve-lifter
rod=, or =push rod=, between them, the cam acting on the rod and
lifting it, and that in turn lifting the valve stem. When the nose of
the cam is not acting on the stem or rod, there must be a small space
between them, for if the stem or rod rests firmly against the cam at
all times, the valve disk might be prevented from seating firmly. The
space is left between the stem and lifter rod, the spring acting only
on the stem.

[Illustration: FIG. 12.—FOUR ARRANGEMENTS OF VALVES.]

The valves may open into the cylinder in a variety of ways; both may
be in one =pocket=, or one may be in a pocket and the other in the
head, or each in a separate pocket, or both in the head. The first
two illustrations show automatic inlet valves, and the third and
fourth mechanically operated valves; when two mechanically operated
valves are in the head, it is necessary to open them by means of
=rocker arms=, for because of their position it would be impossible
for the valve-lifter rod to act directly on their stems.

If after the explosion the burned gases were permitted to escape
directly into the open air from the cylinder, the effect would be the
same as the firing of a gun, and for the same reasons. The pressure
in the cylinder being higher than that of the atmosphere, the sudden
expansion of the gases would produce a report, and as this would be
most undesirable for an automobile, provision is made by which the
gases are cooled and permitted to expand gradually, so that when they
reach the open air they are at its pressure, or nearly so. This is
done in the =muffler=, or =silencer=, to which the =exhaust pipe=
conducts the products of combustion. The muffler consists of a series
of chambers of different sizes, one inside of the other; the gases
pass from the smaller to the larger, expanding as they go, until from
the largest they should escape without noise, having lost their heat
and pressure.

While the pressure exerted during the power stroke depends on the
heat of the gases, and it is necessary to have the engine hot in
order that there may be as little loss of heat as possible, the
temperature must not be permitted to rise to the point at which the
lubricating oil would burn. Lubricating oil for gasoline engines is
made to stand high heat, but if heated beyond its limit it will
burn, and then, besides the loss of its property of lubrication, a
deposit of carbon, hard or gummy, will form, fouling the combustion
space or piston rings, and interfering with the operation of the
engine. Overheating is prevented either by circulating water through
channels surrounding the combustion space, or by directing a blast of
air against it.

[Illustration: FIG. 13.—_A_, Force circulation water-cooling system;
_B_, thermosiphon circulation water-cooling system. (Flow of water
indicated by arrows.)]

The channels, called =water jackets=, provided for the circulation
of the water, are usually cast with the cylinder, or formed of sheet
metal. Cool water enters at the bottom and escapes at the top,
absorbing heat during its passage. Of the two systems of keeping the
water in circulation, the most usual consists of a rotary pump,
which forces the water through the jackets and then to a =cooler=,
or =radiator=, which is so placed that it is exposed to the air
currents set up as the car moves. In order to cool the water, the
radiator must have a large surface exposed to the air, and the water
must pass through it in small streams. The early types consisted of
coils of small copper tubing, on which were strung disks of copper,
the water flowing through the tubing, and the disks absorbing its
heat and giving it up to the air, but these are being abandoned in
favor of =cellular= or =honeycomb= radiators. These types, which are
usually placed at the extreme front of the car, are made up of a
great number of short lengths of small tubing, in any one of several
shapes, placed side by side, and held together either by plates or by
soldering their ends.

[Illustration: FIG. 14.—_A_, Centrifugal pump; _B_, vane pump; _C_,
gear pump and cover.]

[Illustration: FIG. 15.—RADIATOR CONSTRUCTIONS. _A_, Spiral flange
(water passes through the tube); _B_, cellular, and _C_, honeycomb
(air passes through the tubes; water passes between the tubes).]

[Illustration: FIG. 16.—RADIATOR AND FAN.]

The heated water enters at the top of the case in which the tubes
are contained, and flows to the bottom, finding passages between the
tubes, while the air passes through, being assisted by a fan driven
by the engine.

The second system of keeping the water in circulation follows the
principle that heated water tends to rise, its place being taken by
the cooler water that tends to sink. This, called the =thermosiphon=
or =gravity= system, requires all of the parts and connections to
be large and completely filled with water. The water in the jacket
rises as it absorbs heat from the cylinder walls, and flows out to
the radiator, which it enters at the top. Its place in the jacket
is taken by the cooled water from the bottom of the radiator, and
this circulation continues, being more rapid as the difference in
temperature between the heated and cooled water increases. It is
naturally not so rapid as circulation that is forced by a pump, and
more liable to become inoperative by the clogging of the pipes,
jacket, or radiator.

Of the methods of increasing the surface of a cylinder in order to
cool it by a blast of air, the most usual is to cast it with flanges
that project from all parts of the combustion space. These become
heated as the temperature of the cylinder walls increases, and the
air that is blown against them carries off the heat. Other methods
consist of setting pins or copper strips into the cylinder walls, of
such form that the air current strikes a surface composed of points,
by which the heat easily passes to the air. Another system consists
of surrounding the combustion chamber with a jacket open at the
bottom, air being blown into it from the top by a powerful blower.

Other things that are necessary for successful air cooling are large
valves by which the hot gases may be quickly discharged when their
period of usefulness is ended, and small cylinders rather than large,
as the heat from small quantities of gases may be carried off more
quickly than from large.

The lubrication of a gasoline engine must be carefully looked after,
as on its thoroughness depends the continued delivery of power. The
most usual method of lubricating the piston and cylinder walls is to
keep the crank case filled with oil to such a point that the end of
the connecting rod dips into it in turning. This spatters the oil to
all parts of the crank case, and a portion is caught in a groove
cut around the lower end of the piston. The inward movement of the
piston spreads the oil on the cylinder walls, and it is distributed
around the piston rings, so that they move easily in their grooves.
As the oil is used up, it is replaced from a =lubricator= so that a
constant level is maintained, and this operates either by gravity, or
by a small force pump driven by the engine, or by the maintaining of
pressure in the oil tank.

Mechanically operated or pressure lubricators supply oil to all
parts of the engine, and as the quantity passed to each bearing is
adjustable, a feed may be maintained that is exactly suited to the
requirements.

The bearings of an automobile operate under such widely different
conditions that one kind of lubricant will not be suitable for
all. The maker of the car has tested the different oils, and it is
advisable to follow his instructions on the brand and grade most
suitable for each bearing, rather than to try experiments. The
Lubrication Table on pages 244 and 245 gives the kind and quantity of
lubricant most suitable to the work performed by each bearing.




                             CHAPTER III

                           ENGINE BALANCE


A drawback to the use of reciprocating engines is that the weight
of the piston and connecting rod in sliding first one way and then
the other produces great vibration, and that the crank shaft in
bringing these parts to a stop at each end of the stroke is subjected
to violent shocks that in time wear it loose in its bearings. With
internal-combustion engines this vibration, and the shock on the
crank shaft, are greatly increased by the intensity with which the
pressure is exerted.

Engines with one cylinder may be balanced to some extent by the use
of counterweights attached to the crank shaft, and by the use of so
heavy a fly wheel that its momentum produces a comparatively steady
movement; but a perfect absorption of the vibration would require
the engine to be run at a constant speed, which is not possible with
those used on automobiles.

In two-cylinder engines the vibration may be reduced by so arranging
the parts that the pistons slide in opposite directions, the weight
of one being balanced by that of the other. This plan is used in
engines of the =horizontal double-opposed= type, which is considered
to be the most satisfactory for low powers. The cylinders are
horizontal, with their open ends toward each other, the crank shaft
lying between them. The crank shaft is =two-throw=, 180°; that is,
there are two pairs of crank arms, projecting from opposite sides of
the shaft, so that they are a half revolution apart.

Two cylinder engines are also built with vertical cylinders, and are
of two types, according to the construction of the crank shaft. In
one, the crank shaft is 180°, and in the other both pairs of crank
arms project from the same side of the shaft so that the crank pins
are in line, this being called a 360° crank shaft.

In the 180° type one piston moves up as the other moves down, so that
they balance, but it results in the power strokes occurring in both
cylinders during one revolution of the crank shaft, with no power
during the revolution that follows.

To understand the reason for this, the order in which the events of
the cycle occur must be recalled, and it must be remembered that of
the four strokes of the piston during which they are performed the
two outward strokes are inlet and power, and the two inward strokes
compression and exhaust. If the piston of a two-cylinder vertical
engine (Fig. 17) is moving downward on the power stroke, piston No. 2
will be ascending, and the only events that can then be performed in
its cylinder are compression or exhaust. If performing compression,
it will move under power during the next stroke (the other half of
the revolution), No. 1 then exhausting (Table No. 1). This brings the
two power strokes in one revolution, and during the next revolution
there will be no power stroke, for No. 1 will be performing suction
and compression, and No. 2 exhaust and suction.

[Illustration: FIG. 17.—ENGINE ARRANGEMENTS SHOWING ORDER OF FIRING.]

If, as shown in the second table, No. 2 is moving upward on exhaust
while No. 1 moves down under power, its previous stroke, the first
half of the revolution, will have been the power stroke, and the
same condition will exist of two power strokes occurring in the same
revolution.

In either case the balance of the moving parts is offset by the
irregular production of power, which produces bad results in the
setting up of strains in the engine, and the uneven running of the
car.

In two-cylinder vertical engines with 360° crank shaft (Fig. 17) the
pistons move up and down together, which of course results in bad
balance. In this arrangement, however, the applications of power may
be evenly spaced, for as the piston in cylinder No. 1 moves downward
on the power stroke, piston No. 2 moves in the same direction, and
may make either the inlet or power stroke. If it makes the inlet
stroke, it must move inward before it can again move outward on the
power stroke, and there will be an interval of one stroke between the
power strokes of the two cylinders. To have the power strokes in the
two cylinders occur together, as suggested as the alternative, would
obviously give bad results in the great strain imposed on the crank
shaft, the weight of the fly wheel that would be necessary to carry
two pistons through three dead strokes, and the jerky running of the
car.

The defects of two-cylinder vertical engines with either design of
crank shaft outweigh any possible advantage of that construction,
and the horizontal double-opposed type, in evenly occurring power
strokes, mechanical balance, and simplicity, is in almost universal
use for cars of low power.

A two-cylinder engine does not require so heavy a fly wheel as a
one-cylinder engine in proportion to the power delivered, because
there is a power stroke every revolution instead of in alternate
revolutions, and the parts must be carried over only one dead stroke
instead of three. Similarly, the fly wheel of a four-cylinder engine
may be still lighter, for in that type there are two power strokes
in every revolution, with no dead strokes. At the same time, it is
not possible to dispense with it entirely, for the pressure acting
on the piston at the beginning of the power stroke falls rapidly as
the piston moves before it, and the momentum by which the fly wheel
tends to revolve at a constant speed steadies and smooths what would
otherwise be a jerky motion.

The crank shaft of a four-cylinder engine is 180°, four-throw, with
the two end cranks projecting in the opposite direction to that
of the two inside cranks. This arrangement is used in preference
to having the cranks project alternately; that is, the first and
third to one side and the second and fourth to the other, because
of economy in manufacturing, and because practice has shown that it
results in less vibration in the running of the engine.

This construction of the crank shaft does not permit the power
strokes to occur in rotation, cylinder No. 2 following No 1, and then
Nos. 3 and 4, for it has been explained that when cranks are 180°
apart the power strokes occur during one revolution, and that when
360° apart there is a dead stroke between the two power strokes.
Cranks 1 and 2 are 180° apart, as are 3 and 4, and also 2 and 4,
but 2 and 3 are 360°; that is, their crank pins are in line, which
is also the case with 1 and 4. The power stroke in cylinder No. 2
may follow that in cylinder No. 1, but must be followed by that in
cylinder No. 4, as that is 180° away from No. 2, and No. 3 comes
last, being 180° from No. 4. The succession in which the power
strokes occur, called the =firing order=, is thus 1, 2, 4, 3, and
this is arranged for by the setting of the valves and the timing of
the ignition.

This firing order was used for the first four-cylinder automobile
engines, but it has lately been suggested that the firing order 1, 3,
4, 2 shows advantages in the reduction of strains and vibration, and
is being adopted.

Three-cylinder engines are built with 120° crank shafts; that is,
the cranks are one third of a revolution apart, instead of one
half of a revolution, as is the case with 180° crank shafts. This
gives three power strokes during two revolutions, and results in
excellent balance. Six-cylinder engines have crank shafts of similar
construction, and produce six power strokes during two revolutions,
with the best balance that it is possible to obtain without an
excessive number of cylinders. A power stroke occurs at every 120°
that the crank shaft revolves, and as each power stroke endures for
a half revolution, or 180°, it follows that one commences when the
previous one is only two thirds complete. This gives a very steady
application of power, for the crank shaft is at all times operated by
the driving effect of the combustion strokes, and it is possible to
run the engine smoothly at greatly varying speeds by control of the
position at which the spark occurs in the combustion space, and the
admission of a greater or less volume of the mixture during the inlet
stroke.

The type of engine that will give satisfaction depends on the work
that is demanded of it, the care that it will receive, and the
knowledge of the operator. A one-cylinder engine, having a minimum of
parts, may be successfully managed by a novice, but its vibration,
and the fact that it delivers power for only one fourth of the time
that it runs, make it unsatisfactory for any but light work. Cars
of medium power are almost universally equipped with horizontal
double-opposed engines, with excellent results, and they are not
difficult to maintain. More powerful cars have four-cylinder
vertical engines, which give a sufficiently constant pull for all
practical purposes, with a correspondingly greater demand for care
and attention. Six-cylinder engines are of doubtful advantage for
general use, without the services of a chauffeur, for while they
develop more constant power than engines with fewer cylinders, the
complication of parts and the care necessary are increased.




                             CHAPTER IV

                          TWO-CYCLE ENGINE


The two-cycle type of gasoline engine differs from the four-cycle
type described in the foregoing chapters in that the five events
composing the cycle are performed during one revolution of the crank
shaft, or two strokes of the piston, power being developed during
every outward stroke of the piston instead of alternate outward
strokes.

[Illustration: FIG. 18.—TWO-CYCLE ENGINE.]

In order that this result may be attained, the construction of the
engine is changed, and, as will be seen in Fig. 18, the crank case
is utilized as a receiver for the mixture before it passes to the
combustion space. The valves are replaced by =ports=, which are
openings into the combustion space that are covered and uncovered
by the piston as it slides in the cylinder. The =inlet port= is
uncovered when the piston is at the inmost point of its stroke
(Fig. 18, A), and then admits the mixture to the crank case; the
=by-pass port= and the =exhaust port= are uncovered when the piston
is at the outmost point of its stroke (Fig. 18, B), the former then
permitting the mixture to pass from the crank case to the combustion
space, and the latter is that through which the burned gases escape
after combustion has taken place.

During an inward stroke, the pressure in the crank case is reduced
as the piston slides away from it, and fresh mixture is forced into
it by the higher atmospheric pressure as soon as the inlet port is
uncovered. This port is covered when the piston makes an outward
stroke, and the mixture, not being able to escape, is compressed. Its
tendency to expand causes it to flow to the combustion space when
the by-pass port is uncovered, and in entering it strikes a ledge
on the piston so that it is deflected to the top of the combustion
space instead of being able to shoot across the cylinder and out the
open exhaust port. The inward stroke of the piston covers these two
ports and compresses the mixture, ignition occurring in the regular
manner. The pressure developed by the combustion drives the piston
outward, and as soon as the exhaust port is uncovered (which is
slightly before the uncovering of the by-pass port), the gases, which
are still expanding, begin to escape, and are further expelled by the
fresh charge that enters and drives them before it. Thus the five
events of the cycle are performed during an inward and an outward
stroke of the piston, the crank case end of the piston drawing a
charge of fresh mixture into the crank case and forcing it into the
combustion space, and the combustion chamber end compressing it and
being acted on by the pressure from the combustion.

At slow speeds, two-cycle engines have advantages over the four-cycle
type in the production of a power stroke at every revolution of the
crank shaft, and the absence of valves and valve mechanism with their
weight and possibility of giving trouble. This simplicity makes the
two-cycle engine popular for motor boats, where they are run at
slow and constant speed, but for higher and changing speeds these
advantages are outweighed by disadvantages that show little sign of
being overcome.

With the engine running at a thousand revolutions a minute, it can be
understood that the ports will be open for only a brief period during
each stroke, and that the faster the engine runs the shorter will be
the period during which the gases may enter or leave the combustion
space. The inefficiency of two-cycle engines as compared with engines
of the four-cycle type is due entirely to the fact that the burned
gases have not sufficient time in which to escape from the combustion
space, nor the fresh charge time to enter. The fresh charge that does
enter being incomplete, and being contaminated by the portion of the
burned gases that has not been able to escape, result in the “choking
up” of the engine, and in the production of lower power than the
dimensions and weight of the engine should warrant.




                              CHAPTER V

                   CARBURETION AND GASOLINE FEEDS


Pure gasoline vapor will not burn, and in order to render it
inflammable it must be combined with oxygen. The simplest manner
of effecting this is to mix air with it, and when the correct
proportions are obtained, the oxygen supplied by the air will be
sufficient to result in the complete combustion of the gasoline
vapor, without a surplus of either of the ingredients. This mixing
is called =carburetion=, the air being said to be =carbureted=.
A correct proportion of gasoline vapor and air results in rapid
combustion; an excess of air makes combustion slower, and excess of
gasoline vapor prevents the combustion from being complete, a residue
of carbon remaining. The correct proportions of air and gasoline
vapor are obtained by the use of a device called a =carburetor=,
which is connected to the combustion chamber by the =inlet pipe=, and
in such a manner that everything entering the combustion space by the
inlet valve must first pass through it.

Liquid gasoline is led to the carburetor from the supply tank, and
the air enters it when the pressure in the combustion space is
reduced by the piston in making the inlet stroke. The speed with
which the air flows through the carburetor depends on the extent
to which the pressure is reduced, and the gasoline vapor that
is required to form a mixture of the correct proportion must be
maintained in accordance with it. While there are various classes of
carburetors, practically all that are used for automobile engines
are of the =float-feed= type; that is, the supply of gasoline is
maintained by a =float=, just as water tanks are kept filled to a
desired depth by a hollow metal ball that floats on the liquid and
controls the valve by which the water enters.

[Illustration: FIG. 19.—CARBURETOR PRINCIPLES.]

The principal parts of a float-feed carburetor are the =float
chamber= and the =mixing chamber=, the gasoline flowing from the
supply tank to the float chamber, and from there to the mixing
chamber, where it is combined with the air. The gasoline flows out of
the float chamber through a small pipe, the end of which, called the
=spray nozzle=, projects into the mixing chamber so that the current
of air rushes past its tip (Fig. 19). When the inlet stroke is not
being performed, and there is no air passing through the mixing
chamber, the float in the float chamber keeps the gasoline at such
a level that it stands just below the tip of the spray nozzle. In
this condition the gasoline in both the float chamber and the spray
nozzle is under atmospheric pressure; but when the pressure in the
combustion space is reduced as the piston makes the inlet stroke, the
pressure in the inlet pipe and mixing chamber is also reduced, and
the gasoline will be forced out of the spray nozzle by the higher
pressure in the float chamber. The passage in the tip of the spray
nozzle is small, and the gasoline is broken up into fine drops as
it spurts out, and in this condition is partly absorbed by the air
and partly carried into the cylinder. By regulating the amount of
gasoline that may pass out of the spray nozzle, it may be adjusted
to the volume of air flowing through the mixing chamber, so that any
desired proportion may be obtained.

If the engine were to be run at a constant speed, the relative
pressures on the gasoline in the float chamber and spray nozzle,
and the quantity of gasoline forced out of the spray nozzle, would
remain in correct proportion to the volume of air; but as the engine
of an automobile is run at greatly varying speeds, the pressure in
the mixing chamber is not constant, but varies to correspond. If
the piston makes fifty inlet strokes a minute, the reduction of the
pressure in the mixing chamber is more gradual than would be the
case with the piston making two hundred inlet strokes a minute. The
more rapidly the pressure is reduced, the greater will be the effect
of the unchanging atmospheric pressure in the float chamber, and
the more gasoline will be forced out of the spray nozzle. This will
result in the presence of too much gasoline in proportion to the air,
giving a mixture that is =too rich=. It is therefore necessary to
provide an arrangement by which the pressure in the mixing chamber
will not be changed as the speed of the engine varies, and this is
accomplished by the =auxiliary air inlet=, which is closed when the
engine runs slowly, but opens to correspond with increasing speed
(Fig. 19). The faster the engine runs, the more the auxiliary air
inlet will open, to admit a correspondingly greater amount of air to
prevent the pressure in the mixing chamber from being reduced below
the point at which the required amount of gasoline is forced out of
the spray nozzle.

The most rapid combination of the gasoline and air is secured by
breaking the gasoline up into fine spray as it leaves the nozzle.
In order to break the gasoline into fine particles, the tip of the
spray nozzle is made with a fine opening, and often forms the seat
for the gasoline adjusting valve, which is a needle-pointed rod that
is screwed in or out to reduce or enlarge the opening; a further
breaking up results from the placing of a metal cone, or the end of a
rod, in such a position as to be struck by the gasoline as it flows
out.

A carburetor with an auxiliary air inlet is provided with two
points of adjustment, to control the flow of gasoline from the
float chamber to the spray nozzle, and to govern the admission of
the auxiliary air. The flow of gasoline must be just sufficient to
carburet thoroughly the air passing through the mixing chamber when
the engine runs at low speed, and the auxiliary air inlet must open
to correspond with increasing speed, to admit sufficient air to keep
the pressure reduced to proper proportions.

The auxiliary air inlet may be operated either by the reduced
pressure that permits the atmospheric pressure to open a valve, or
by the governor of the engine, which opens the inlet as the speed
increases, and closes it on slowing down. The first of these two
types, called an =automatic carburetor=, is in most general use for
automobiles, and is sufficiently satisfactory, but is not as accurate
as the =mechanically controlled= type, which acts independently of
pressure, and exactly according to the speed of the engine.

[Illustration: FIG. 20.—AUTOMATIC CARBURETORS.]

Carburetors may be divided into two types, according to design:
those in which the float and mixing chambers are side by side, and
those in which the mixing chamber passes through the center of the
float chamber (Fig. 20). The former is along the lines of the first
forms of float-feed carburetors, and the latter is of more recent
design, its object being a more compact device, and one that is not
affected by a change of level when the car is on a hill. Both have
advantages and disadvantages, and the use of one as against the other
is optional and a matter of opinion.

The carburetors illustrated are not of any particular makes, and are
intended to show principles rather than construction.

In carburetors with a side mixing chamber the float is usually a
metal box, the joints of which are as far as possible proof against
leakage. Guides prevent it from having any but an up-and-down motion,
and in thus moving it controls the gasoline inlet valve by a rod
attached to it, or by a separate valve stem. In this carburetor a
separate valve stem is used, and it is moved through the action
of a rocker arm controlled by the float. This construction is
usual when the gasoline enters the float chamber from the bottom,
the flow being permitted or checked by a needle valve. When the
level in the float chamber drops as the gasoline runs out of the
spray nozzle, the float sinks, and lifts the valve point from its
seat. This admits gasoline from the supply tank, and the float in
rising on it depresses the valve point, shutting off the flow. The
gasoline adjusting valve is in the passage between the float and
mixing chambers. The main or initial air inlet is in the side, the
air being drawn through the mixing chamber, and past the spray
nozzle. The auxiliary air inlet is a simple valve, opening inward,
and held against its seat by a coil spring, the tension of which
is adjustable. The pressure in the mixing chamber being reduced in
accordance with the increasing speed of the engine, the valve is
opened more and more as the atmospheric pressure against the outer
surface of the valve overcomes the tension of the spring.

In carburetors with central mixing chamber the float is ring- or
horseshoe-shaped, and usually made of cork, well varnished to prevent
the absorption of the gasoline. The air enters at the bottom, passing
directly to the mixing chamber. The auxiliary air inlet is at the
top, and is of the arrangement already described. The mixture passes
out at the side, and may be controlled by a =throttle=, which may be
a damper arrangement, as shown, or other device by which the quantity
passing to the combustion space is at the will of the operator.

The float and mixing chambers of a mechanically operated carburetor
are the same as in the side-float chamber type, the difference being
in the control of the auxiliary air inlet (Fig. 21). This consists of
a tube attached to the mixture outlet, within it sliding another tube
moved by the governor as that expands or contracts with the speed of
the engine. There are openings in the sides of both tubes, but when
the sliding tube is at its inmost position these are not in line,
and consequently are closed. When the governor acts with increased
engine speed, the sliding tube is drawn out, and one or more openings
come into line, air entering through them to the mixing chamber.
The faster the engine runs, the larger become the openings, and in
consequence the greater is the amount of air that they admit. The
illustration shows the ball type of gasoline valve, the ball on the
end of the valve stem being drawn against its seat as the float rises.

[Illustration: FIG. 21.—MECHANICALLY CONTROLLED CARBURETOR.]

While these types are in practically universal use for automobile
engines, there are other methods by which the proportions of the
mixture may be maintained. In one form the gasoline drops on a funnel
made of fine wire gauze, which is placed in the mixing chamber in
such a manner that the air in entering passes through it. The liquid
forms a film over the gauze, and is picked up by the air, as it is
in a condition that permits it to evaporate rapidly. In surface
carburetors air is forced through the gasoline tank, or through an
absorbent material soaked with gasoline, and becomes thoroughly
saturated. This mixture is then thinned with pure air until the
desired proportion is obtained, when it passes to the combustion
space. The objections to these forms arise from the clogging of the
parts with the impurities present in gasoline, and while they give
excellent results when new, they deteriorate rapidly and present such
resistance to the flow of the air current that they become useless.

[Illustration: =Fig. 22.=—FLOAT FEED CARBURETOR WITH GRAVITY GASOLINE
FEED. 1, Filling cap; 2, tank; 3, gasoline valve; 5, trap and
strainer; 6, carburetor; 7, float chamber; 8, float; 9, float valve;
10, spray nozzle; 11, gasoline adjustment; 12, air adjustment; =13,
throttle=; =14, mixing chamber=; =15, initial air inlet=; 16, primer.]

There are two methods of supplying the carburetor with gasoline. Of
these the most usual is the =gravity feed=, in which the tank is
placed at a higher level than the carburetor, so that the gasoline
flows down to it. The tank is usually placed under the seat, and the
piping so arranged that the carburetor is the lowest point of the
system. This method of feeding is satisfactory if the tank can be
placed sufficiently above the carburetor to have the flow unaffected
by an ordinary hill, but if it is not so placed, a steep ascent may
tilt the car to such an extent that the carburetor is above the level
of the gasoline in the tank, in which case the flow of course ceases.

The =pressure feed=, which has been adopted on all high-grade cars,
operates through the maintenance of pressure in the supply tank, the
gasoline being forced out without regard to gravity. The tank is
tight, so that the pressure cannot escape, and is connected by a long
pipe of small diameter either with the combustion space of one of the
cylinders or with the exhaust pipe, so that the pressure of the
burned gases is maintained in it. As the pressure cannot exist until
the engine is running, a hand air pump is usually provided, by which
a sufficient pressure may be produced in the tank to force out enough
gasoline for starting. It is necessary to use as long a pressure pipe
as possible, in order to prevent the possibility of flame passing
through it to the supply of fuel, a long pipe, exposed to the air,
cooling the gases to such an extent that they cannot ignite the
gasoline.

[Illustration: FIG. 23.—PRESSURE FEED GASOLINE SYSTEM. 1, Filling
cap; 2, tank; 3, pressure pipe; 4 and 5, check and relief valves;
6, hand pump; 7, check valve; 8, pressure gauge; 9, feed pipe; 10,
carburetor.]

The pressure pipe is always fitted with a =check and relief valve=,
which acts as a safety valve in preventing the pressure in the tank
from reaching a point at which the joints might be strained, and
also retains the pressure which would otherwise escape when the
engine stops. In some cars an auxiliary gasoline tank is provided on
the dash, being fed by pressure from the main tank, and from which
gasoline flows to the carburetor by gravity. The short distance
of this tank from the carburetor and its elevation prevent the
possibility of the flow being stopped by any tilting of the car short
of an upset.

[Illustration: FIG. 23A.—TYPES OF FLOAT VALVES.]

Because of the liability of the presence of water in the gasoline,
as well as dirt and grit, the gasoline line should be fitted with
a =strainer=, or =trap=. This may be in any position, but it is
usual to have it close to the carburetor, if not built into it. The
simplest strainer consists of a number of thicknesses of fine wire
gauze, so arranged that it may be easily taken out for cleaning. This
will separate the dirt from the gasoline, and water may be caught in
a trap, which is a pocket where the water, being heavier than the
gasoline, may settle and be drawn off.


                          CARBURETOR PARTS

Practically all the carburetors on the market are combinations of a
few forms of float valves, auxiliary air inlets, and spray nozzles.
In addition to the forms shown in Figs. 20 and 21, the most usual
float valves may be seen in Fig. 23A. In the first two types shown
in this diagram, the float valve stems are separate from the floats,
and are sufficiently heavy to shut off the flow of gasoline by their
weight. In the third type, the gasoline enters the float chamber
from the top, and as the valve stem is attached to the float, the
rising of the float results in the shutting off of the gasoline. The
fourth type is in use on carburetors with central mixing chambers,
the float being hinged to one wall of the float chamber. The loose
valve stem is supported by the hinge, and rises to a seat in the
valve when the gasoline is at the proper depth on the float chamber.

[Illustration: FIG. 23B.—TYPES OF AUXILIARY AIR INLETS.]

Fig. 23B illustrates the most usual forms of auxiliary air inlets.
In the first type, the valve disk slides on the valve stem, and
enlarges the size of the main air inlet. All of the air thus passes
the spray nozzle. In the second type, the inlet for the auxiliary
air is separate from the main air inlet, the two currents meeting
in the mixing chamber, and the extra air diluting the rich mixture
that is formed at the spray nozzle. This action is more correct in
theory than that of the preceding type, and better practical results
are obtained from it. These air valves are defective in opening
and closing too abruptly, and in tending to vibrate rather than to
remain open a fixed distance. The air inlet illustrated in the fourth
diagram was designed to overcome these faults. When the engine is
not operating, the air inlets are closed by a hollow piston that
is held up by a spring. The upper part of the piston rod carries a
metal disk that is attached by a flexible leather washer to the walls
of an upper chamber. The portion of the chamber above the disk is
tightly closed, except for a small hole in the cover that provides
the only communication between the atmosphere and the air confined in
the chamber. When the engine runs at speed, the atmospheric pressure
against the upper side of the disk is greater than the pressure
against the lower side, and the disk is therefore forced downward
against the action of the spring. The movement of the disk moves the
piston, and as this latter slides downward it uncovers the openings
and admits air. The small size of the opening in the cover prevents
air from entering or leaving the chamber above the disk rapidly,
and the movement of the piston is therefore steady and free from
jerks. The third diagram illustrates two positions of a mechanically
operated auxiliary air inlet, controlled by a governor.




                             CHAPTER VI

                              IGNITION


The charge of explosive mixture in the combustion space is ignited,
or set on fire, by an electric spark, and the apparatus for producing
and controlling this spark is called the _ignition system_. It is
with this part of the mechanism of an automobile that a novice has
the greatest difficulty, for an electric current is usually regarded
as being surrounded by an air of mystery. It does its work silently
and without visible reason, and when it fails the average man is
under the necessity of beginning at the beginning and examining all
of the parts of the system because he has so little understanding
of the why of it that he is unable to locate trouble in any but a
rule-of-thumb method. The principles of electricity may be involved,
but the production of a current, its handling, and the uses to which
it may be put are not difficult to understand.

Speaking broadly, the parts of the ignition system are the source
of current, the arrangement in the combustion space at which the
spark is produced, the device by which the instant when the spark
passes may be controlled, and the circuit by which these parts are
connected. Before going into a description of these, however, it is
necessary to understand something of the nature and action of an
electric current.

Every generator of electricity has two =terminals=, or =poles=, and
the flow of current from one to the other is due to what may be
explained as a difference in pressure between them. This difference
in pressure is similar to that existing when two tanks, one full of
water and the other empty, are connected by a pipe. The water will
flow from the full to the empty tank as long as there is a difference
in level, which is the same thing as a difference in pressure,
the flow ceasing when the water in one tank is level with that in
the other. When a path is provided between the two poles of the
generator, the current will flow from one to the other, always in the
same direction, leaving by the =positive pole= and returning by the
=negative=.

Because of this tendency to flow, the current may be made to perform
work, for it will light a lamp, ring a bell, or do anything else
within its power in order that it may flow from the positive pole of
the generator to the negative. In this there is also a similarity to
the two tanks, for if a water wheel is placed in the pipe connecting
them, the flow of water from one to the other will operate it.

The path over which the current flows may be formed of any
=conductor= of electricity, such as carbon or any metal; substances
by which the current will not flow are called =nonconductors= or
=insulators=, and those in most common use are rubber, china and
glass, wood, wood fiber, mica, etc.

While all metals are conductors, some are better than others, the
difference being in the =resistance= that they offer. A comparison
illustrating resistance may be made between the friction presented
to the flow of water by a small pipe and by a larger one, the water
flowing more easily through the latter than the former. In flowing,
the current must overcome the resistance of the conductor, and in so
doing will lose part of its strength and will heat the conductor,
there being more loss of current and greater heat as the resistance
increases.

It is obvious that in order to obtain a current of the greatest
strength the conductor by which it flows must present the least
possible resistance, and for this reason copper is used almost
universally to convey the current from one place to another. A copper
wire will carry safely a current that would heat an iron wire of the
same size to the melting point. The resistance of a small conductor
is much greater than that of a large one, so that the size of a
conductor must always be considered in relation to the current that
is to be conveyed.

A current of electricity may be measured, just as water flowing
through a pipe may be measured, and by the same measurements of
pressure and volume. The pressure under which the current flows is
measured in =volts=, and the quantity that passes in =amperes=; there
is also a term for resistance, that being measured in =ohms=.

Because of the desire of the current to flow from the positive to the
negative pole, the circuit must be so guarded that there may be no
leakage, for if it can return to the generator without doing its work
it will do so, taking any path that offers less resistance to its
passage. Leakage is prevented by insulating the wires, which may be
done by wrapping them with silk or cotton thread, or by coating them
with rubber. The wire by which the current flows from the generator
to its work is called the =lead= (pronounced leed), and the conductor
by which it flows back, the =return=. The greatest care must be taken
that there is no leakage from the lead wire in order that there may
be enough current to perform the work; but when the current has done
what was expected of it, any conductor that does not present too much
resistance will serve to return it to its source.

While wire is sometimes used on ignition circuits for the return as
well as the lead, the most usual method is to utilize the metal of
the engine to return the current to its source. The engine being
made of iron, it is a conductor, and while this metal is not so
good a conductor as copper, yet there is so much of it in an engine
that its resistance need not be considered. This method is called
=grounding the return=, the term coming from telegraphy, in which the
dampness of the earth forms one of the conductors.

A grounded circuit requires careful insulation of the lead wire,
for as it is very likely to come into contact with the metal of the
engine, a break in the insulation would permit the current to leak
and to return to the generator without doing its work, this condition
being called a =short circuit=. Grounding the circuit saves wire and
reduces complication; simplicity is important in automobile work, and
a reduction of the parts much to be desired.

In the foregoing the word flow has been used in describing the action
of an electric current in a wire, and there are so many points of
similarity with the flow of water in a pipe that the term conveys a
better idea than would technical expressions. Electricity, however,
has neither substance nor weight, and cannot be said to flow or to
move in the strict sense of the words; but as flow is in general use,
and is the most descriptive of the commonly understood words that are
applied to it, it is made use of here.

A current of electricity may be generated either chemically or
mechanically, and always at the expense of something else. A chemical
generator produces a current at the expense of a metal, usually
zinc, which is eaten by the chemicals in proportion to the amount of
current delivered; a mechanical generator produces a current at the
expense of the power that drives it.

Chemical generators are of two kinds, =primary= and =secondary=
cells. While primary cells are of many forms, that called the =dry
cell= is universally used for the ignition of automobile engines,
being adapted to the purpose because there is nothing to spill, and
may be used in any position. It consists of a zinc cup lined with
some material of the nature of blotting paper, in which, but not
touching it, is a stick of carbon, the space between being filled
with absorbent material and broken bits of carbon moistened with the
proper chemical solution. The top of the cell is sealed to prevent
evaporation, and thumb nuts on the projecting end of the carbon stick
and the zinc cup form the terminals to which the wires are attached.
The carbon being the positive pole and the zinc the negative, the
current flows in that direction whenever a circuit is provided.

The dry cell gives a current at a pressure of about one and a half
volts when new, the voltage dropping as the cell is used until it
is exhausted, when the trifling cost of a new cell should not be
considered in replacing it.

A better source of current than the dry cell is the secondary or
=storage cell=, which is a reservoir rather than a generator. When
a current of electricity is passed to it, usually from a lighting
circuit, a chemical change takes place, the action being called
the charging of the cell. When the change is complete, the cell is
disconnected, and will then deliver a current because the parts of
the cell that underwent a chemical change tend to return to their
previous condition. The current that it gives off is practically
equal to that by which it was charged, and may be used steadily or
intermittently until the cell is exhausted. It is made of prepared
lead plates, which are placed in a hard-rubber or celluloid jar, with
a cover to prevent the spilling of the solution with which the plates
are covered.

The charging of storage cells must be done by an expert, for
mishandling will ruin them, and it is far better to put this matter,
as well as repairs, in the hands of a man who knows his business than
to attempt it without the proper knowledge and appliances.

One point that the automobilist must watch, however, is the position
and quality of the solution in the cells, called the =electrolyte=.
The cells should always be full enough to have the plates well
covered, and any loss by leakage or splashing should be made up, for
the plates must not be exposed to the air.

Electrolyte is made by adding one part of chemically pure sulphuric
acid to from three to four parts of distilled or rain water, adding
the acid slowly and stirring constantly. The combination of acid and
water generates heat, and care must be taken not to pour the water
into the acid, for the generation of heat would then be so sudden
that the mixture would boil and splash, burning whatever it touched.
By means of an instrument called a =hydrometer=, the density of the
mixture may be ascertained, and when the proportions are correct the
scale should read 1,200. Hydrometers are made with the instrument
inside of a glass tube, one end of which has a spout, the other
being fitted with a rubber bulb. By inserting the spout in the vent
hole of the cell cover, the tube may be filled with electrolyte, the
hydrometer showing whether or not it is of the correct density.

The cells should be tested every little while, and if the density is
not correct acid or water should be added to make it so. Never probe
inside of the cells with anything but a glass or hard-rubber rod, for
metal would cause a short circuit between the two plates it touched,
and probably ruin the cell.

The terminals of a storage cell are marked in order to distinguish
them, the symbols being the plus (+) sign for the positive pole and
minus (-) for the negative, these being universally used in this way
on all electrical work. In some makes of storage cells the positive
pole in addition is painted red and the negative black.

A storage cell when fully charged gives a current at a pressure of
about two and a half volts; the voltage drops as the cell is used,
and when it gets down to 1. 8 volts it must be recharged. When a
storage cell is discharged, it should be recharged immediately, for
otherwise it will deteriorate.

One dry or storage cell does not give a sufficient current to
supply the required spark, and several must therefore be used. The
most usual method of connecting dry cells, and the only method of
connecting storage cells, to form a battery, is to connect the
negative pole of the first cell to the positive pole of the second,
using a short length of insulated wire of sufficient size, the
negative of the second to the positive of the third, and so on, until
all of the cells necessary to supply the required current are used.
This leaves the positive pole of the first cell and the negative pole
of the last cell free to be connected into the circuit. The current
obtained will have a pressure that is as much greater than the
pressure of one cell as there are cells in the battery; for instance,
if there are four cells in the battery, of one and a half volts each,
the voltage of the battery will be six volts. This method is called
connecting in =series= (Fig. 24).

[Illustration: FIG. 24.—BATTERY CONNECTIONS.]

When the voltage of one cell is sufficient, and it is desired to
increase the volume, or amperage, of the current, the cells may be
connected in =parallel=, which is done by connecting together all
of the negative poles by one wire, and all of the positive poles by
another, the two wires leading to the circuit. This increases the
amperage as many times as there are cells.

If it is desired to connect the cells so that both the voltage
and amperage are increased, the cells may be divided into two or
more groups, with the same number of cells in each. The cells
of each group are connected in series, and the free poles of
the groups connected in parallel, which is called connecting in
=series-multiple= (Fig. 24). This is a most satisfactory method of
connecting the cells for an ignition circuit, for it gives a uniform
current, and increases the life of the cells. The voltage of the
current is equal to the voltage of one cell multiplied by the number
of cells in one group, and the amperage that of one cell multiplied
by the number of groups.

The action of a mechanical generator, which when driven produces a
current of electricity, is due to magnetism, that being understood
to be the power sometimes possessed by iron or steel to attract
other pieces of iron or steel. Magnetism may be manifested either by
permanent or electro-magnets. If a piece of steel is magnetized—that
is, made a magnet—it continues to be a magnet, for steel retains that
property, while iron does not. A magnet made of steel is called a
=permanent magnet=.

If a piece of iron is wound with insulated wire through which
an electric current passes, the iron will become a magnet, and
will remain so as long as the current flows. This is called an
=electro-magnet=.

The two ends of a magnet are the positive and negative poles, and the
positive pole of one magnet will repel the positive pole and attract
the negative pole of another magnet. Between the two poles of a
magnet there is a constant flow of what are known as =magnetic lines
of force=, which may be made visible by laying a piece of paper over
the two poles and scattering iron filings on it. The filings will
form into curves from one pole to the other, showing the presence of
these lines.

If a wire is moved across these lines of force, so that it cuts them,
a current of electricity will be set up in it, and if the wire is
wound into a coil and moved across the lines, the current will be as
much stronger as there are turns of wire cutting them. A mechanical
generator consists of a coil of insulated wire, arranged so that as
it revolves in the =magnetic field= each turn of wire cuts across the
lines of magnetic force.

The magnet producing the lines of force that compose the magnetic
field is called the =field=, and the revolving coil of wire the
=armature=.

Mechanical generators for producing the current for an ignition
circuit are of two types, =magnetos= and =dynamos=, the former being
in much more general use than the latter. In a magneto the field is
a permanent magnet, and in a dynamo it is an electro-magnet. The
magnets forming the field of a magneto are bent into horseshoe shape,
so that the poles are close together, and the armature revolves
between them. The field of a dynamo is of similar shape, wound with
insulated wire, the current that flows through it being generated by
the dynamo itself; the field is strongly magnetized only when the
dynamo is running.

The armature of either type is a piece of soft iron, with grooves
cut in it lengthways, in which the wire is wound; the winding thus
being contrary to that of thread on a spool. The current generated
in the wire of the armature is taken off by means of =brushes=, and
connection is made through binding posts set in the base.

As the care of a mechanical generator requires a knowledge of
electrical engineering, it is better to return it to the makers in
case of injury, rather than to attempt to repair it without the
necessary experience. (See Appendix.)

Practically all ignition circuits are provided with two sources of
current, so that in case of the failure of one the other will be
available, and either may be connected into the circuit by means of
a =switch=. The simplest form of switch is a piece of flat spring
brass, pivoted at one end so that the other may be swung from side
to side to make contact with one or the other of two brass knobs, or
=switch points=. One pole of each generator, usually the negative,
is grounded, and the other connected to one of the points. The flat
spring, or =switch blade=, is connected to the ignition circuit, so
that when it is in contact with one of the points the corresponding
source is called on to supply the current. The blade may rest between
the points, not touching either, in which case the circuit is broken,
and no current flows.




                             CHAPTER VII

                       IGNITION—(_Continued_)


While there are various methods by which an electric spark may
be produced, but two are in use for automobile work, one being
the =high-tension= or =jump-spark system=, and the other the
=low-tension= or =make-and-break system=. The difference between
these is in the pressure of the current, which in the first is great
enough to enable it to jump from one terminal to another a short
distance away, forming a spark as it passes. The pressure of the
current of the low-tension system is not sufficient to permit it
to do this, but when two terminals of the system are brought into
contact so that the current may flow, a spark will form as they are
separated.


                        MAKE-AND-BREAK SYSTEM

In the make-and-break system, the =igniter=, which is the device
in the combustion space at which the spark occurs, is made with
two metal points, one of which is stationary and the other movable,
the latter being acted on by a cam, through a =tappet=. As the
cam revolves, the tappet is lifted and the movable point brought
into contact with the stationary; when the nose of the cam passes
from under the tappet, the movable point is snapped away from the
stationary through the action of a spring (Fig. 25). These points
are so connected into the circuit that when they are in contact the
current flows, the circuit being broken when they separate. Shortly
before the spark is desired the movable point is brought into contact
with the other so that the circuit is completed and the current
flows, and they are separated at the instant when the spark is
required to ignite the mixture, this occurring as they separate and
break the circuit.

[Illustration: FIG. 25.—MAKE-AND-BREAK IGNITION.]

The current that is supplied by the battery is not capable of
producing this spark, for it flows with large volume and small
pressure—i.e., high amperage and low voltage—and it is necessary
to transform it to a current of higher voltage and lower amperage,
which is done by means of a =primary induction coil=. A coil of this
description consists of a =core= made of a bundle of soft iron wires,
around which is the =primary winding=, formed by winding several
layers of insulated copper wire on it. The core becomes a magnet when
a current of electricity flows through the winding, and ceases to be
a magnet when the flow ceases, the magnetization occurring slowly on
the completion of the circuit, and demagnetization instantly on the
breaking of the circuit.

The influence of a magnet, as, for instance, its attraction for a
piece of iron, is felt throughout a field the extent of which depends
on the strength of the magnetization. When a loop of wire forming
a closed circuit is placed in the =magnetic field=, a current of
electricity will be set up in it whenever the strength of the field
changes. If the strength of the field does not change, no current
will be set up; but the greater the change in strength, whether
from strong to weak or from weak to strong, the greater will be the
strength of the current. This principle is applied in the case of a
coil, for the wire that forms the winding is in the magnetic field of
the core, and a current is set up in it whenever the strength of the
field changes. The strongest current will be set up, or =induced=,
when the strength of the field changes from no magnetism to a degree
when the core is magnetized to its fullest capacity or the reverse,
and when the change occurs in the least possible time. The current
that is set up will last only during the time when the change in
strength occurs, ceasing to exist when the strength of the field is
uniformly strong or weak. The more rapid the change, the greater will
be the pressure of the current, but the shorter the period of its
existence.

It is this induced current that forms the spark in the combustion
space, the battery current serving only to establish the condition
that will produce it. When the two points of the igniter come into
contact and complete the circuit, the flow of the battery current
through the winding of the coil will gradually magnetize the core,
and on the igniter points being separated, this flow through the
winding will cease, the strength of the magnetic field dropping
instantly from full intensity to practically nothing. This change
induces a powerful current in the winding, which current in passing
over the circuit causes a spark between the points of the igniter
as they separate. The induced current is set up so instantaneously
on the breaking of the battery circuit that the spark is usually
considered as being that of the battery current, but, as stated,
the battery current serves only to magnetize the core, the spark
resulting from the current induced by its demagnetization on the
breaking of the circuit.

A magneto is a machine that when driven generates an electric
current, and is in almost universal use for this system of ignition.
In many cars the system is so arranged that the driver has his choice
between ignition by battery and coil, as described, and ignition by
magneto, but the mechanical production of a current is so reliable
that many automobile builders rely on the magneto alone. Magnetos of
the type used for ignition are described in the appendix.


                          JUMP-SPARK SYSTEM

The jump-spark or high-tension system of ignition depends on the
production of a current at such a pressure that it can jump from one
point to another through high resistance, such as is presented by air
at ordinary or low temperature, and especially when compressed, the
spark occurring as it passes.

This high pressure is obtained through the use of a =secondary
induction coil=, which consists of a core and primary winding similar
to those of the primary induction coil already described, and in
addition has a =secondary winding=, formed by a great length of
insulated copper wire, which to save bulk and weight is very fine,
wound over the primary winding. The change in the strength of the
magnetic field produced by the core affects this secondary winding,
just as it affects the primary winding; that is, a current is set
up in it at every change in the strength of the magnetic field, the
pressure of the current depending on the greater or less extent of
the change, and the rapidity with which it occurs. The magnetization
of the core takes place but slowly, for the particles of iron
must absorb it one from the other, but the demagnetization occurs
instantly; the current that is induced during the demagnetization
is therefore the greater, and is the current that has sufficient
pressure to jump across the gap.

The ignition system employing this coil consists of two distinct
parts: the =primary circuit=, which magnetizes the core, and the
=secondary circuit=, which leads to the combustion space the current
that is induced in the secondary winding.

The primary circuit includes the battery or generator that supplies
the current, the primary winding of the coil, a =timer=, and a
=vibrator=.


                              THE TIMER

The spark must occur in the combustion space only at the instant
when the mixture is in a condition to be ignited, and it is obvious
that only then is the secondary current required. As the secondary
current results from the flow of the primary current through the
primary winding, a device must be included in the primary circuit to
permit the current to flow and magnetize the core at this instant.
This device is called a =timer=, or =commutator=, and is nothing more
than a revolving switch operated by the engine, that completes the
primary circuit at such times as the secondary current is required,
and breaks the circuit when the secondary current has done its work
in the production of the spark. Because ignition occurs but once in
each cylinder during two revolutions of the crank shaft, the timer
completes the circuit but once in that interval, and is placed on the
half-time shaft that operates the exhaust valves. In its simplest
form, a timer consists of a disk of hard rubber, wood fiber, or
other insulating material in which is set a metal plate, mounted on
the half-time shaft and revolving with it. A flat spring carried on
a plate of hard insulating material bears against the edge of the
disk, and during one revolution of the latter the metal plate set
in it will be brought into contact with the spring (Fig. 26, first
diagram). If one wire of the primary circuit is connected to the
metal plate of the disk and the other wire to the spring, it will be
seen that the circuit will be complete when the revolution of the
disk brings the two together, and broken when the further revolution
of the disk separates them.

[Illustration: _ONE CYLINDER_ _TWO CYLINDER_ _FOUR CYLINDER_ FIG.
26.—TYPES OF TIMERS.]

There is a great variety in the methods by which this result is
secured, the chief essential being that the contact must be made as
positively as possible in order that the resistance to the current
in passing from one part of the timer to the other may be as low
as possible, and broken equally positively. The number of contacts
that the timer makes during one revolution depends on the number of
cylinders of the engine, the revolving part touching two, three,
four, or more springs or contact points on the stationary part as
it turns. A timer for a two-cylinder engine is shown in the second
diagram on Fig. 26, the third diagram being of a form of timer in
which the revolving part is not connected into the circuit, but
serves to bring together a spring and a contact point, the circuit
being completed when they touch. A modern form of timer consists of
a ring of hard rubber on the inside face of which are set the metal
plates, while the moving part revolves within it, and may be a flat
spring, or a plunger, or a roller, contact being maintained by a
coil spring. The difficulty of attaching a wire to the moving part
of the timer is overcome by having its contact in connection with
the half-time shaft, the current flowing from the contact on the
stationary part to that on the moving part, and from there flowing by
the half-time shaft to the ground connection of the battery, for, as
all parts are of metal, the current can pass from the shaft to the
ground connection through the bearings and the engine.

If the spark were always required to pass in the combustion space at
the same point in the stroke of the piston, this could be secured
by setting the stationary part of the timer in such relation to the
moving part that contact would be made when the half-time shaft
reached any desired point in its revolution. As it is necessary to
change the point at which ignition occurs, however, the timer must be
so arranged that it closes the circuit earlier or later, according
to conditions. To effect this, the stationary part of the timer is
so made that it may rotate around the shaft for about a half turn,
and it is controlled by a lever on the steering column, which holds
it in any desired position. If the stationary part is rotated in the
direction opposite to that in which the half-time shaft revolves,
contact will be made and the circuit closed at an earlier point
in its revolution than if it is rotated in the same direction. It
must be remembered that the revolution of the half-time shaft, in
operating the exhaust valve, revolves exactly in accordance with the
crank shaft and the movement of the piston, and that as the moving
part of the timer is attached to it, contact can be made at any
desired point in the stroke of the piston by the position in which
the stationary part is placed.


                            THE VIBRATOR

The secondary current occurs whenever the core is magnetized and
demagnetized, and it is clear that the oftener the magnetization
occurs the more constant will be its presence. The timer closes and
opens the primary circuit, which results in the production of but two
impulses of the secondary current, and as these are not sufficient
to produce the necessary spark, additional means are employed to
make and break the circuit while the timer makes contact. This is
accomplished by means of a =vibrator=, or =trembler=, which consists
of a flat steel spring secured at one end, so that it may vibrate
after the manner of a tuning fork. About midway between its ends the
point of an =adjusting screw= touches it, and when the flat spring,
or =blade=, vibrates, it springs away from this screw and returns
to it, both screw and blade being tipped with platinum to offset
corrosion. If one wire of the circuit is attached to the blade and
the other to the screw, the circuit will be complete when the blade
touches the screw, and broken when it springs away from it. In the
early type of vibrator the blade was set in vibration by mechanical
means. At the end of the blade was a weight, which rested on the edge
of a cam, the blade then being out of contact with the adjusting
screw (Fig. 27). During the revolution of the cam the weight dropped
into a deep notch, thus setting the blade into vibration and the
circuit being made and broken. This type has been almost entirely
superseded by the =magnetic vibrator=, which is more rapid and
accurate. In this the blade is so placed that its free end is close
to the end of the core of the coil (Fig. 28). When the timer makes
contact and the current passes through the primary winding, the core
becomes magnetized and attracts to it the free end of the steel
blade, this movement drawing the blade away from the adjusting screw
with which it was in contact. The vibrator is so connected into
the primary circuit that the current flows from the battery to the
adjusting screw, thence to the blade and through the primary winding;
when the attraction of the blade by the core draws it away from
the adjusting screw, the circuit is broken, and the magnetism then
ceasing to exist, the elasticity of the blade causes it to spring
back to the screw, to make contact, and to be again attracted by the
magnetism.

[Illustration: FIG. 27.—MECHANICAL VIBRATOR. When the weight drops
into the notch on the cam, the flat spring touches the adjusting
screw and the current passes.]

[Illustration: FIG. 28.—MAGNETIC VIBRATOR. When the magnetism of the
core attracts the vibrator the contact is broken at the adjusting
screw.]

This action continues as long as the timer holds the circuit closed,
and a wave of secondary current is set up in the secondary winding
for every make and break that results. By means of the adjusting
screw, the vibrations may be made long and slow, or short and quick,
with a corresponding difference in the secondary current. As the
object to be attained is the production of a spark that will ignite
the mixture rapidly, the vibrator must be adjusted with this end in
view; but it is also advisable to obtain the spark with the least
possible expenditure of current, and with the least wear of the
parts. The passing of the battery current through the primary winding
establishes the condition that exists in the make-and-break ignition
system, and the demagnetization of the core will set up an induced
current that will result in a spark at the points where the circuit
is broken; that is, at the vibrator and timer contacts. This spark
can be greatly overcome in the timer by packing it with vaseline,
which, being an insulator, breaks down the spark in flowing between
the contacts of the stationary and moving parts as they separate.
If the vibrator contacts presented no resistance—an impossible
condition—there would be no spark, but as they will always be
slightly burned and corroded, the spark must be kept as small as the
requirements of the secondary current will justify by the adjustment
of the screw. In other words, adjust the vibrator so that it gives
the best results in the production of the secondary spark with as
little sparking as possible at the vibrator contacts.


                           THE SPARK PLUG

The secondary circuit includes the secondary winding of the coil
and the =spark plug=, which is the device in the combustion space
at which the spark occurs. The spark plug provides two points of
metal at a fixed distance apart, which are so connected into the
circuit that the current must jump from one to the other in order to
complete its circuit. The secondary current, as well as the primary,
may make use of the metal of the engine as a ground return, and one
of the points of the spark plug is therefore in contact with the
metal, being supported on a metal sleeve that is screwed into the
cylinder. The other point must of course be insulated from it, for
if it were not the current could pass from one to the other without
jumping the space between them. The insulation is secured by a tube
of porcelain or mica set in the sleeve, the lower end of a metal rod
that passes through it being the required distance from the wire or
projection on the sleeve (Fig. 29). This device must be strong enough
to resist the pressure in the combustion space during the compression
and power strokes, and must be unaffected by the intense heat.

[Illustration: FIG. 29.—_A_, Spark plug; _B_, spark plug in section.]


                             THE CIRCUIT

Fig. 30 shows the primary and secondary circuits of the jump-spark
system, as applied to a one-cylinder engine, the light lines
representing the primary circuit and the heavy lines the secondary.
Each circuit forms a complete path by which the current passing
over it may return to the point at which it started. In practice
the wiring is simplified by the use of but one ground return for
both circuits, the primary and secondary windings of the coil being
connected at one point, and the secondary current returning either
through the timer as it makes contact or through the battery.

[Illustration: FIG. 30.—IGNITION CIRCUIT. Wiring diagram for
one-cylinder engine, with coil, timer, and two batteries; coil with
magnetic vibrator.]

The flow of the primary circuit is from the battery to the switch,
to the vibrator, which is built into the coil, through the primary
winding and the timer contacts, whence it passes by the metal of the
engine and ground wire back to the battery. The secondary circuit
consists of a wire from the secondary winding of the coil to the
spark plug, and back to its winding by the metal of the engine and a
ground wire, which, as has been explained, may be the separate ground
wire shown in the diagram, or the return that is common to both
circuits.

The timer makes contact as the half-time shaft revolves, and the
vibrator operates as long as the circuit is closed; while this
occurs, the secondary current is set up, and the spark passes.

Included in the primary circuit and built into the base of the coil
is a =condenser= which, while of such delicate construction that it
is most inadvisable for the automobilist to attempt to examine or
repair it, is of such advantage that it should be understood. A
current flowing in a circuit possesses momentum, and if the circuit
is broken, the momentum will cause the current to flow across the
break for a greater or less time, according to the pressure. This
will produce a spark, and a spark at the vibrator as it breaks the
circuit will not only burn away the contacts, but will prevent the
instant demagnetization of the core. The passing of a spark between
the vibrator contacts indicates that the current is still flowing
through the primary winding, and that the core is still magnetized.
The function of the condenser is to prevent sparking at the vibrator
by absorbing the momentum of the current, and, what is more
important, to cause the instant demagnetization of the core by the
instant breaking of the circuit.

While it is usual to provide a multicylinder engine with one coil
for each cylinder, it is possible to equip it with but one, in such
a case a =secondary distributer= being used. This consists of two
parts: a primary timer, and a somewhat similar device by which the
secondary current induced in the coil is switched from cylinder to
cylinder as it is required. For a four-cylinder engine the timer
has four contacts, as in the usual type; but the primary winding is
connected to all of them, so that as the moving part of the timer
revolves, the core of the single coil is magnetized four times to two
revolutions of the crank shaft. A single wire leads the secondary
current that is thus induced to the distributer, by which it is
switched to the several cylinders. The moving part of the distributer
rotates in unison with the moving part of the timer, making contact
as it does so with contact pieces, each of which is connected to one
of the spark plugs.

When the timer makes its contact the distributer is in position to
pass the induced current to the proper cylinder, the connections
being made in accordance with the firing order of the engine. While
this system has advantages in that there is but one vibrator to
adjust, the fact that the coil is operating for the greater part
of the time makes it more liable to injury through heating and the
consequent breaking down of its insulation.




                            CHAPTER VIII

                            TRANSMISSION


The =transmission= of an automobile consists of those parts that
transmit to the driving wheels the power developed by the engine.


                             THE CLUTCH

Because a gasoline engine must be in operation before it can deliver
power, a =clutch= is provided by means of which it may run free or
be so connected that it drives the car, one of its two chief parts
being attached to the engine and the other to the transmission.
When the two parts are in contact, the transmission is driven, and
when separated, the engine and transmission are independent of each
other, and may be stationary or in motion. A clutch must be of such
a nature that it does not apply the power of the engine instantly,
but gradually, so that the car starts slowly and without jerking.
If the power were to be applied suddenly, the effort of starting the
stationary car would either overcome the momentum of the engine and
stop it, or would jerk the car into such sudden motion that it might
be badly wrenched. By making the clutch so that it is permitted to
slip when first applied, the part that is driven is gradually brought
to the speed of the part that drives, when slipping ceases and the
two make firm contact.

The most usual form of clutch is the =friction cone=, in which the
fly wheel of the engine is utilized as the driving part, the rim
being broad and thick, with its inner side funnel-shaped, or beveled.
A metal =cone= that fits the bevel is carried on the end of a shaft
of the transmission, the shaft at this point being square, to fit
a square hole in the hub of the cone. This arrangement permits
the cone to slide along the shaft while always revolving with it.
When the cone is pressed to a seat in the fly wheel, which is
accomplished by means of a heavy coil spring, the friction between
its leather-covered surface and the surface of the fly wheel causes
the two parts to revolve together, and by its fit on the square
shaft the transmission is set in motion, and through that the car.
The clutch is thrown out of contact by means of a foot pedal that
acts on a ring fitting in a groove around the hub of the cone; when
the pedal is released, the spring forces the cone to its seat (Fig.
31). In order to support it, the end of the shaft carrying the cone
projects into the hub of the fly wheel, where it rests in a bearing,
this arrangement in no manner preventing the two parts from acting
independently of each other.

In the =reversed type= of friction-cone clutch a funnel-shaped ring
is bolted to the rim of the fly wheel and forms the seat, the cone
fitting inside of it (Fig. 31). Depressing the pedal moves the cone
toward the fly wheel instead of away from it, as in the regular type,
and while there is no difference in the effect of one as against the
other, the reversed type is more compact.

[Illustration: _FRICTION CONE CLUTCH_ _REVERSED FRICTION CONE CLUTCH_
FIG. 31.—FRICTION CONE CLUTCHES.]

The =multiple-disk clutch=, which is rapidly coming into use, depends
on the friction between the flat surfaces of metal when pressed
together. An experiment illustrating this is to place a silver
dollar between two half dollars, and to press them together between
the thumb and finger. It will be found that a light pressure is
sufficient to produce friction that will make it difficult to revolve
the large coin between the smaller ones.

The parts of a simple form of multiple-disk clutch, as shown in
Fig. 32, are a =flange= on the engine shaft, a smaller flange with
a square-hole, square-shaft arrangement on the transmission shaft,
and large and small =rings= placed alternately. The large rings are
driven by the large flange, fitting loosely on pins, or =studs=,
projecting from it, and the small rings are similarly attached to
the transmission shaft. The openings in the large or driving rings
are large enough to contain the studs carrying the small rings, so
that when the parts are assembled the outer surfaces of the small or
driven rings are in contact with the inner surfaces of the driving
rings. A heavy coil spring is arranged to press the small flange
toward the flange on the engine shaft, binding the rings that it
carries between the driving rings, and the latter are often faced
with leather to increase the friction between them. When the small
flange is released from the pressure of the spring by depressing
the pedal, the driving and driven flanges with their rings are
independent of each other, and the engine may run free while the
transmission shaft is stationary or revolving. A clutch of this type
is incased and runs in oil, which prevents the rings from gripping
suddenly; when the pressure of the spring is applied, the oil is
gradually squeezed out from between them, and the slipping of the
driving and driven rings is reduced as they are forced into contact.

[Illustration: _PARTS OF MULTIPLE DISK CLUTCH_

_MULTIPLE DISK CLUTCH ASSEMBLED_

FIG. 32.—MULTIPLE DISK CLUTCH.]

An =internal-expanding= clutch consists of a broad ring, or =drum=,
against the inner surface of which bear two pieces of metal shaped to
fit. The pieces of metal, or =shoes=, are pivoted together at one end
so that they may be moved in or out, after the manner of the handles
of a pair of scissors; when open they bear against the inside surface
of the drum, and when closed they are free from it. The drum is
attached to the engine shaft and the shoes to the transmission shaft,
the friction between them being so great that the transmission shaft
is carried around as the drum revolves. The shoes are kept in contact
with the drum by a coil spring, the depression of a pedal releasing
them from its pressure.


                       CHANGE-SPEED MECHANISM

The =change-speed mechanism=, to which the clutch transmits the power
of the engine, is to the engine what a block and tackle is to a man
who lifts a heavy weight, and is necessary because of the varying
resistance to the movement of the car in traversing steep, rough
hills and smooth avenues. A change-speed mechanism may be defined as
an arrangement by which the relative number of revolutions of the
crank shaft and driving wheels may be altered to suit conditions.
If the driving wheels revolve but once while the crank shaft makes
twelve revolutions, the car will move at one sixth the speed that it
would have if the wheels revolved once to every two revolutions of
the crank shaft, but it will have six times the ability to overcome
the resistance presented by a hill or sandy road.

If a gasoline engine were so connected that the relative number of
revolutions of the crank shaft and wheels could not be changed,
a slowing down of the car through the resistance presented by a
rough hill would slow the engine to correspond, and as speed is an
important factor in the power that the engine delivers, it would be
prevented from doing the work of which it is capable at the time
when it was most necessary. By means of the change-speed mechanisms
in most general use, the relative number of revolutions of the crank
shaft to one of the wheels may be varied to from two to eighteen, the
former giving the car high speed over a smooth road, and the latter
slow speed, but greater ability to overcome hills and heavy roads.

To attain this result, gears are used. If two gears having the same
number of teeth are in mesh, they will make the same number of
revolutions, and the force with which the driven gear will revolve
will be the same as that of the driving gear, less the friction of
the teeth. If the driven gear has twice the number of teeth of the
driving gear, it will revolve at half the speed, but with twice the
force.

The forms of change-speed mechanism most largely used are based on
this principle, which is so applied that the gear driven by the
engine may be in mesh with a gear that has many more teeth and
revolves much slower in consequence, or a gear that has possibly
one and a half times the number of teeth, or a gear that has the
same number of teeth, and therefore revolves at the same speed. The
=sliding-gear= mechanism takes its name from the arrangement by which
the changes in the combination of gears is effected by sliding them
along a shaft, to mesh with other gears on a shaft driven by the
engine.

[Illustration: _NEUTRAL_ _SLOW SPEED_ _SECOND SPEED_ _HIGH SPEED_
_REVERSE_ FIG. 33.—SLIDING GEAR—PROGRESSIVE TYPE. _A_, Sleeve driven
by engine; _B_, gear on sleeve; _C_, gear on countershaft; _D_,
low-speed gears; _E_, second-speed gears; _F_, idler for reverse;
_G_, clutch for high speed; _H_, connected to rear wheels; _J_, gears
sliding on square shaft.]

The driver changes the gears by moving a lever that in the
=progressive type= moves forward by degrees to move the car on
the slow speed, the intermediate speeds, and the high. A typical
arrangement of the progressive type of sliding change-speed mechanism
is shown in Fig. 33. The power of the engine is transmitted to a
short, hollow shaft, called a =sleeve= (_A_), which carries a gear
(_B_) that is in permanent mesh with a gear (_C_) on the end of the
=countershaft=. Parallel to the countershaft is another shaft, one
end of which is held in a bearing in the hollow sleeve; while the
sleeve supports this shaft, the two may revolve independently of each
other. The second shaft is square, or of such a construction that
while the two gears that it carries may slide along, they revolve
with it. The gears on the square shaft are of different sizes, and
in sliding on it come successively into mesh with gears carried on
the countershaft. Because of the gears between them, the countershaft
revolves when the engine revolves the sleeve; but the speed of the
square shaft depends on the combination of gears in mesh between it
and the countershaft. When the sliding gears are in such a position
that they are not in mesh with the countershaft gears, the square
shaft is independent of the countershaft, and may revolve or be
stationary, the gears then being in the =neutral position=. When
the sliding part is moved so that its largest gear is in mesh with
the smallest of the countershaft gears (_D_), the square shaft will
revolve at a slower speed than the countershaft, because its gear
is larger than the one driving it. Again sliding the moving part
will separate these gears, and bring the next pair (_E_) into mesh,
the square shaft then moving at a higher speed, but still slower
than the countershaft because of the difference in the size of the
gears. Sliding the moving part still farther along the shaft will
disengage the =second-speed= gears and engage the =high speed=, in
which the square shaft revolves at the speed of the sleeve and crank
shaft, this being effected by locking the moving part to the sleeve
by means of a clutch (_G_). This clutch consists of several fingers
projecting from the moving part, corresponding to the spaces between
similar fingers on the end of the sleeve. The locking together of the
square shaft and sleeve gives what is known as the =direct drive=,
which is of comparatively recent development; many designs of sliding
gears still use a third pair of gears which, being of the same size,
give the square shaft the speed of the crank shaft. By the use of
the direct drive, the power of the engine is directly applied to the
square shaft, avoiding the loss that occurs through the friction of
the teeth of the gears.

The revolution of the square shaft is transmitted to the driving
wheels, the speed of the car therefore corresponding to the speed at
which the square shaft is driven by the gear combinations between it
and the countershaft. To obtain the =reverse=, which enables the car
to be backed without reversing the engine, a third gear is introduced
between the low-speed gears of the square shaft and countershaft.
When two gears are in mesh, they revolve in opposite directions,
but when one of them is in addition meshed with a third gear, the
first and third will revolve in the same direction, and opposite to
the direction in which the middle gear revolves. When the car is
going forward, the square shaft and countershaft revolve in opposite
directions, but when the reverse gear is introduced between them, the
square shaft is revolved in the same direction as the countershaft,
reversing the rotation of the driving wheels.

The ends of the teeth of the gears are chisel-shaped, instead of
being flat, as in ordinary gears, so that they will go into mesh
easily.

The greatest economy in the operation of a gasoline engine results
from its running at as nearly constant a speed as possible, and the
gear is therefore changed when the resistance of the road to the
movement of the car decreases the speed of the engine, or permits it
to increase.

The =selective type= of sliding change-speed mechanism as shown on
Fig. 34 is in use on many of the high-grade cars, and its control
differs from that of the progressive type described in that the lever
has only a short movement forward and back, and in addition may slide
sideways. To the lower end of the lever is attached a shaft that
rocks in its bearings as the lever is moved forward or back, and
slides lengthways when the lever is moved toward or away from the car.

[Illustration: FIG. 34.—SELECTIVE TYPE. _A_, Sleeve driven by engine;
_B_, fixed gear on sleeve; _C_, fixed gear on countershaft; _D_,
low-speed gears; _E_, second-speed gears; _F_, third-speed gears;
_G_, clutch for direct drive; _H_, rod and arm for third-speed and
direct drive; _J_, rod and arm for low and second speeds; _K_, rod
and arm for reverse, _L_, rocking-shaft finger in groove; _M_, guide
plate and control lever; _N_, bevel gears on square shaft and jack
shaft; _O_, idler gear for reverse.]

The arrangement of the countershaft and square shaft is the same as
in the progressive type, but there are two sets of sliding gears
instead of one, and these are moved by means of arms that extend
from rods sliding in bearings at the side of the gear case. When
these rods are slid endways, the gears attached to their arms slide
on the square shaft to correspond, and go in or out of mesh with
the countershaft gears. Across the ends of these rods are grooves,
which when the gears are in the neutral position are in line with the
rocking shaft attached to the control lever. From the inward end of
the rocking shaft a finger (_L_) projects downward into the groove;
when the grooves are in line, the rocking shaft may be slid endways,
the finger passing from one groove to the next without affecting the
rods. When the shaft is rocked, however, the finger in engaging one
of the grooves slides the rod endways, shifting the gears controlled
by its arm. Moving the control lever into such a position that it may
enter the middle slots of the guide plate (_M_) slides the rocking
shaft so that its finger projects into the groove of the central
sliding rod (_J_), and if the control lever is then pushed forward
so that it enters the front half of the slot, the sliding rod will
be moved by the finger in the opposite direction, and the low-speed
gears (_D_) will be brought into mesh. Bringing the lever back to the
central position will separate the gears, and moving it to the back
half of the slot will slide the same gears in the opposite direction,
meshing the second-speed combination (_E_). Moving the control lever
outward so that it is in line with the outside slot brings the finger
into the groove of the sliding rod (_H_) that moves the third and
high speeds (_F_ and _G_), the latter being direct drive, and the
reverse is obtained through the movement of the sliding rod (_K_)
that is engaged by the finger when the control lever is in the inside
slot. The movement of this rod brings a third gear (_O_) into mesh
with the low-speed gears on the square shaft and countershaft, and
the rotation of the countershaft is reversed.

While this type is in general use, the gears are often so arranged
that the direct drive combination is reached when the control lever
is in the third-speed position, the gears meshed by the fourth-speed
position driving the square shaft at a still higher speed. This high
speed can only be used for running under the best road conditions.

The advantages of the selective type over the progressive are the
shorter movements of the control lever and the ability to pass from
one speed to any other without the necessity of first meshing and
unmeshing those between, or, in other words, there is a neutral
position between every combination of gears, and from neutral any
desired combination may be obtained directly without reference to the
others.

In starting up a car fitted with either of these types of
change-speed mechanism, it is necessary to withdraw the clutch before
sliding the gears, and this is also necessary in changing from one
combination to another. The square or corresponding shaft of a
change-speed mechanism is always connected with the driving wheels,
and is at rest when the car is standing. With the engine running, the
countershaft will be revolving, and it will obviously be difficult to
slide the stationary gear into mesh with a gear that is revolving.
When the clutch is withdrawn, the countershaft moves only through
momentum, and will be brought to a stop by the contact of the teeth
of the sliding gear as that is moved against it, the two then easily
going into mesh. The clutch is then thrown in slowly, and will bring
the speed of the countershaft to the speed of the crank shaft.

When the car is moving, sliding the gears without first withdrawing
the clutch will bring together two gears that are revolving at
different speeds, and as it is necessary for them to be rotating
equally in order that they may mesh, either the speed of the car
must be changed to bring the speed of the gear on the square shaft
to that of the countershaft gear, or the speed of the engine must
be changed to bring the countershaft gear to the speed of the gear
on the square shaft. If the change is from a low to a higher speed,
the countershaft will be moving much faster than the square shaft,
and their gears being brought into contact will result in the
slowing of one and speeding up of the other until the speeds are
the same, but in so doing the ends of the teeth will grind against
each other, resulting in the wear of the chisel-pointed ends, if not
in the breaking of the teeth. Withdrawing the clutch obviates this
difficulty, for it frees the countershaft, permitting its gear to
take the speed of the square-shaft gear without wear or damage, and
when the change is made, the slow engagement of the clutch brings the
speed of both to that required by the crank shaft.




                             CHAPTER IX

                     TRANSMISSION—(_Continued_)


While the =planetary type= of change-speed mechanism, which is in
extensive use for runabouts and light commercial wagons, also employs
gears, their arrangement is along different lines. The first three
diagrams in Fig. 35 serve to illustrate the principle.

[Illustration: _REVERSE_ _SLOW SPEED_ _HIGH SPEED_ _PRINCIPLES OF
PLANETARY GEAR TRANSMISSION_ _SECTION PLANETARY GEAR TRANSMISSION_
FIG. 35.—PLANETARY TYPE.]

The gear _A_ in these diagrams is attached directly to the crank
shaft, and in mesh with it are four other gears (_B_) of the same
size. Surrounding them is an =internal gear= (_C_), this being a
ring with teeth cut on its inner face, the four gears meshing with
it. The shafts, or =studs=, on which the four gears revolve are
supported by a metal ring (_D_), which maintains the gears at equal
distances from each other. The first diagram shows the mechanism in
the reverse position, for driving the car backward, the car being
driven by the internal gear. To have the internal gear revolve in the
direction opposite to that of the crank shaft, as is necessary, the
ring supporting the four gears is held stationary, with the result
that as the crank-shaft gear revolves the four gears are revolved on
their studs. As these gears are in mesh with the internal gear, that
is revolved, and moves in the same direction as the four gears and in
the opposite direction to the crank shaft.

For the low-speed forward, the ring is released and the internal gear
held stationary, the car now being driven by the ring instead of by
the internal gear. If the four gears were free from the internal
gear, they and their ring would revolve with the crank-shaft gear
without rotating on their studs, but being in mesh with the internal
gear, they roll around it as a wheel rolls along the ground, rotating
on their studs. A simple experiment that will illustrate this motion
is to crook the forefinger around a napkin ring or similar object,
placing a pencil between it and the finger, and revolving the ring
with the other hand. The finger being stationary, the pencil, which
is revolved in the opposite direction to the ring, will roll along
it. In this the napkin ring represents the crank-shaft gear, the
pencil one of the four gears, and the finger the internal gear. As
the four gears roll around, the ring moves also, for it is carried
by the studs on which the four gears revolve. If each of the four
gears has fifty teeth, and the internal gear two hundred teeth,
each gear must make four revolutions in order to roll around the
internal gear to the point where it started. The crank-shaft gear
also having fifty teeth, it revolves at the same speed, and as four
revolutions of the four gears are necessary in order that they may
roll completely around the internal gear, the crank-shaft gear will
make four revolutions in the same time. The ring moves with the four
gears, and revolves once around the crank shaft in the same time. As
the car moves according to the rotation of this ring, it will go at
one quarter the speed that it would make if the wheels were directly
connected with the crank shaft instead of with the ring.

For the high speed, the internal gear and the ring are locked to the
crank shaft so that all revolve together, the wheels being driven by
either the ring or the internal gear.

In these diagrams the drive of the wheels is supposed to be shifted
from the internal gear to the ring, which is not a practical
arrangement, and the planetary change-speed mechanism as applied to
an automobile is shown in the lower diagram in Fig. 35.

In this there are two sets of crank-shaft gears, gears and rings,
and internal gears, one set being for the reverse and the other for
low and high speeds. Between the two crank-shaft gears is a loose
sleeve, one end of which forms the internal gear for the reverse,
and the other end the ring supporting the studs on which revolve the
four gears for the low speed. The sprocket for the chain drive to
the rear axle is carried on this sleeve. Two more loose sleeves are
on the shaft, one forming the ring on which revolve the four gears
for the reverse, and being extended to form a brake drum outside of
the internal gear, and the other carrying the internal gear for the
low-speed combination, its outside face serving as a brake drum.

To obtain the reverse, a brake band is tightened on the drum of the
reverse combination, which holds stationary the ring supporting the
four gears, giving the result shown on the first diagram of the four
gears revolving on their studs, and rotating the internal gear in the
direction opposite to that of the crank shaft. The sleeve bearing the
sprocket is thus revolved, and the car backs.

For the low speed, the reverse brake band is loosened, and the
internal gear of the low-speed combination held stationary by the
tightening of the brake band surrounding its drum. The revolution
of the crank-shaft gear causes the four gears to revolve on their
studs and to roll around the internal gear, revolving the ring and
the sleeve bearing the sprocket, which now turns in the direction
opposite to that resulting to the application of the reverse, or in
the same direction as the crank shaft.

For the high speed, a clutch is engaged that locks the internal
gear to the crank shaft, and the four gears then being held between
these two are carried around with them, and the sprocket rotates
accordingly. When this combination is used, none of the gears are in
motion, all revolving with the crank shaft but not on their studs.

The planetary change-speed mechanism gives excellent results for
light work, but having only two speeds forward is not adapted to
high-powered cars. As the speeds result from the tightening of brake
bands on the drums, there is no danger of damaging the gears by
mishandling, for the brakes will slip before the teeth will give
way. The brakes, which are leather-lined strips of steel, require
attention from the wearing of the leather, and the slipping that
results from oil working in between them and their drums. No foot
clutch is necessary, for the tightening and loosening of the brake
bands is controlled by a lever; in some designs, the reverse is
applied by means of a foot pedal, and this may be used in braking the
car.

[Illustration: _NEUTRAL—INDIVIDUAL CLUTCH DRIVE—LOW SPEED_ _HIGH
SPEED_ _LOW SPEED_ _REVERSE_ SINGLE FRICTION DRIVE _HIGH SPEED_
_LOW SPEED_ _DOUBLE FRICTION DRIVE_ FIG. 36.—INDIVIDUAL CLUTCH AND
FRICTION DRIVE.]

The =individual-clutch= type of change-speed mechanism consists
of two shafts, one being an extension of the crank shaft, and the
other parallel to it (Fig. 36). On the crank shaft is a sleeve
bearing the sprocket and a gear, this sleeve being so arranged
that it may revolve loosely, or be locked to the crank shaft and
made to revolve with it by a clutch. The crank shaft in addition
bears two fixed gears, one being for the low speed and the other
for the reverse. On the countershaft is a fixed gear in mesh with
the gear carried on the sleeve on the crank shaft, and two loose
sleeves bearing gears that are in mesh with the fixed low-speed
and reverse gears on the crank shaft. These sleeves are provided
with clutches by which they may be locked to the countershaft to
revolve with it, or disconnected from it. When the three clutches are
disengaged, the crank shaft in revolving carries with it the fixed
low-speed and reverse gears, the sleeve bearing the sprocket and
gear remaining stationary. The sleeves on the countershaft revolve
because their gears are in mesh with the fixed crank-shaft gears, but
the countershaft remains stationary. In engaging the low speed, the
clutch is thrown in, forcing the countershaft to revolve with the
fixed gear, the fixed gear on the countershaft then revolving the
gear and driving sprocket carried on the sleeve on the crank shaft.
Because of the difference in the size of the gears, the countershaft
will revolve at a slower speed than the crank shaft, and the driving
sprocket will make but one revolution while the crank shaft makes
several. This it is free to do, for the sleeve carrying the sprocket
is in no way connected with the crank shaft. For the high speed,
the low-speed clutch is withdrawn, and the driving-sprocket clutch
engaged, causing the sprocket to revolve with the crank shaft.

The reverse is caused by the introduction of an idler gear between
the gears of the crank shaft and countershaft, by which the movement
of the latter is reversed.

The application of the =friction type= of change-speed mechanism to
automobiles is recent, and is giving good results for light work. It
consists in its simplest form of a heavy disk carried on the engine
shaft, on the face of which runs a wheel sliding on a square shaft,
so that the two may be in contact at any point from the edge to the
center of the disk (Fig. 36). When the wheel is at the center of the
disk it is not moved, and the number of speeds at which the square
shaft may be driven in relation to that of the disk varies from
nothing to the limit, which is obtained when the wheel is in contact
with the outer edge of the disk. For the reverse, the wheel is moved
across the center of the disk, where it is revolved in the opposite
direction.

Another form of friction drive provides two driving disks, the wheel
bearing against both, so that its movement is more positive, and
there is less chance for slipping.


                             FINAL DRIVE

From the change-speed mechanism the power is passed to the driving
wheels by the =final drive=.

[Illustration: FIG. 37.—_A_, Propeller or driving-shaft drive; _B_,
single-chain drive.]

In the most usual construction the engine is so placed that the
crank shaft is at right angles to the axle, and it is therefore
necessary to change the direction in which the power acts, which is
done by means of =bevel gears=. In ordinary spur gears the teeth
are parallel to the shaft, and the two shafts that carry them are
parallel, while in bevel gears the teeth are at an angle, and the
shafts may be at right angles to each other. In Fig. 37 the diagram
of the =single-chain drive= illustrates a car in which the engine is
in the center of the frame, and as the crank shaft is parallel to
the axle, the power may be directly applied. In the illustration of
the =propeller= or =driving-shaft drive= the crank shaft is at right
angles to the axle, and the power is turned by means of the bevel
gears at the rear axle.

The single-chain drive can only be used for light cars, and is
usually applied in connection with a change-speed mechanism of the
planetary type.

[Illustration: FIG. 38.—TYPICAL UNIVERSAL JOINT.]

The propeller-shaft drive requires the use of =universal joints=,
which are devices that permit one shaft to drive another, even though
they are at an angle with each other. A typical universal joint is
illustrated in Fig. 38. The ends of the shafts bear yokes, the ends
of which are pivoted to a block of metal of + shape. When the two
shafts are in line, the joint will force one to rotate with the
other, and this will not be prevented if the two are out of line, for
then the pivots will act, the + swinging on its pivots in the yokes.

[Illustration: FIG. 38A.—TYPES OF SHAFT DRIVES. DRIVE THROUGH
UNIVERSAL JOINTS “STRAIGHT LINE” DRIVE GEAR BOX ON REAR AXLE]

The change-speed mechanism is carried on the frame of the car, and
is therefore supported by the springs, but the axle end of the
driving shaft follows the axle as that follows the inequalities of
the road. One end of the propeller shaft is therefore comparatively
stationary, while the other is in constant motion, and if the shaft
were inflexible it would be jammed in its bearings and twisted out of
line. This is prevented by the universal joints with which the shaft
is provided, there being one and often two in the shaft, and usually
one between the clutch and change-speed mechanism.

[Illustration: FIG. 39.—LIVE AXLE—NON-FLOATING TYPE.]

[Illustration: FIG. 40.—LIVE AXLE—FULL FLOATING TYPE.]

The single-chain and driving-shaft drives require the use of a =live
axle=, which is an axle that revolves with the wheels. The simple
type of live axle consists of the shaft to which the wheels are
attached, and the =housing= that contains and supports it (Fig. 39).
This axle is continuous, and usually has square ends that fit into
the square hubs of the wheels so there may be no slipping. The
second diagram in Fig. 40 shows a live axle of the =floating= type,
in which the revolving part serves only to turn the wheels. The
housing is extended, and the wheels run on its ends, the driving part
projecting beyond the housing and having square ends that are secured
to the outside of the hubs by square caps. The wheels thus run on the
housing, which takes the weight of the car from the driving part. A
live axle must be divided into two parts in order that a differential
gear may be fitted, and the housing must therefore be strong enough
to support the weight and prevent sagging. The efficiency of a bevel
gear is greatly reduced if the teeth are not in their exact mesh, and
sagging of the axle will throw them out to such an extent that they
will be noisy, and wear rapidly. The floating type of live axle, in
relieving the driving part of the weight, has a great advantage over
the simple type, and is in general use.

[Illustration: FIG. 40A.—DEAD AXLE WITH DRIVING SHAFT. Axle supports
Bevel Gear and Differential. The Driving Shaft is supported in
Bearings at the Differential end, and drives the wheels through
clutches in the hubs.]

With the driving-shaft drive it is necessary to use a =torsion rod=,
which extends from the gear case, or a crosspiece of the frame,
to the rear axle. The necessity for this is the tendency of the
driving bevel gear to roll around on the driven bevel gear rather
than to revolve it. If it were not for the torsion rod, there would
be a continual strain on the parts because of the tendency of the
axle housing to revolve around the axle, instead of the axle being
revolved inside of the housing. The torsion rod has a flexible joint
at one end, that permits it to give as the axle follows an uneven
road surface, but it retains the housing in the correct position,
preventing the bevel gears from getting out of line (Fig. 41).

[Illustration: FIG. 41.—TORSION ROD.]

[Illustration: FIG. 42.—DOUBLE SIDE-CHAIN DRIVE.]

In Fig. 42 is shown a car with =double-chain drive=, in which the
bevel gears that change the direction in which the power is applied
are contained within the =gear case= that incloses the change-speed
mechanism. As will be seen from Fig. 34, the bevel gears connect the
square shaft with the =jack shaft=, which is a shaft passing across
the car, and bearing on its ends the sprockets by which the wheels
are driven. This type of drive requires the use of a =dead axle=,
which is stationary with the wheels running loose on its ends, like
the axle and wheels of a coach. An axle of this type may have great
strength with light weight, and is usually a manganese-bronze or
steel forging. The sprockets on the rear wheels are bolted to the
spokes, and should be, of course, exactly in line with the sprockets
on the jack shaft in order that the chains may run true.


                            DIFFERENTIAL

When a car takes a corner, the outside wheels make a larger curve
than the inside, and cover a longer distance. As the front wheels
are loose on the axle, they accommodate themselves to this; but as
both rear wheels are driven by the engine, it is necessary to apply a
device that will permit them to rotate at different speeds without
interfering with their driving the car. This is accomplished by means
of a =compensating and differential gear=.

To understand the necessity for a differential, stand behind a wagon,
with one hand on each tire; push, and if the vehicle is steered
straight ahead, the hands will move ahead equally; but if the vehicle
turns, the hand on the outside wheel will move ahead faster than the
other. Now take a stick, and run it through the rear wheels so that
it bears against the spokes; press it forward from its center, and if
the vehicle moves straight ahead, the stick will go forward equally;
but if the vehicle turns, the outside end of the stick will go ahead
faster and farther than the other, although the pressure is being
applied to its center.

[Illustration: _BEVEL GEAR TYPE_ _SPUR GEAR TYPE_ FIG.
43.—DIFFERENTIALS.]

In applying a simple form of differential the axle is divided into
two parts, to the inner ends of which are fitted bevel gears, these
being held at a fixed distance apart by the construction of the
housing (Fig. 43). Between the bevel gears and in mesh with both of
them are small bevel gears, or =pinions=, which may revolve on
short studs carried on a ring so that they are a fixed distance
apart. When the ring is revolved it carries with it the studs and
pinions. The ring forms a housing that incloses the differential, and
is driven by the single chain or driving shaft. To understand the
action of the differential, imagine the rear wheels of a car to be
jacked up clear of the ground so that they are free to revolve, and
the housing to be revolved by hand. As it turns, the driving wheels
will turn also, for the resistance to each is the same, and the
pinions, being in mesh with both bevel gears, cannot revolve on their
studs. If one of the wheels is now held stationary and the housing
revolved, the bevel pinions will revolve on their studs, and roll
around on the stationary gear; this will drive the gear of the free
wheel at twice the speed of the housing. The revolving of the housing
in the first instance caused the wheels to turn equally at the speed
of the ring, and in the second permitted one to remain stationary
while the other turned at twice the speed of the housing, the speed
of the latter being unchanged. The first is the effect when the car
moves straight ahead, and the second the result if the car could
make so short a turn that it would pivot on one wheel.

With the wheels jacked up, hold one hand lightly against one of the
wheels, so that while it may turn, there is more resistance to it
than to the other. If the housing is now revolved, the bevel pinions
will revolve on their studs, and roll slowly around the gear of the
wheel that presents the resistance, the free wheel being revolved at
a higher speed than the housing. This is the condition when the car
takes a corner, for there is then more resistance to the inside than
to the outside wheel, and it slows down; this will start the pinions
revolving on their studs, and they will drive the outside wheel
correspondingly faster.

With the housing revolving at a fixed speed, the outside wheel will
revolve as much faster as the inner wheel is revolving slower; for an
illustration, if the housing makes fifty revolutions a minute, and
the inner wheel is slowed to forty, the outer will be driven at sixty
revolutions.

If one wheel of a jacked-up car is revolved by hand, the other wheel
will revolve in the opposite direction. This is caused by the
housing remaining stationary and the pinions being revolved on their
studs by the turning of the wheel, the movement being transmitted to
the free bevel gear and wheel in the reverse direction.

The bevel gear differential described was the early type, but a more
recent design employs spur gears. The axle ends carry spur instead of
bevel gears, these being in mesh with other spur gears that are long,
but of small diameter. These small gears are in pairs, as shown in
Fig. 43, being in mesh with each other at their inner ends, and each
member of a pair meshing with one of the axle gears. The small gears
revolve on studs supported by the housing that is revolved by the
drive, the studs in this case being parallel with the axle instead of
at right angles to it, as are the studs in the bevel-gear type.

If the small gears meshed only with the axle gears, and not with each
other, revolving the housing would cause them to roll around the axle
gears, all rotating on their studs in the same direction, and the
axle gears remaining stationary. Being in mesh with each other, they
cannot revolve in the same direction, for when two gears are in mesh
they must revolve in opposite directions. Thus the small gears cannot
roll around on the axle gears when the housing is revolved, and if
there is equal resistance to the turning of the wheels, the small
gears will not revolve on their studs, but will carry the axle gears
with them.

If the car is turning a corner, the greater resistance to the inner
wheel will cause the small gears to revolve on their studs, rolling
around the resisting gear and driving the other correspondingly
faster.

On cars with double-chain drive, the differential is fitted to the
jack shaft, and of course receives the drive from the change-speed
mechanism through its housing.

Both the driving-shaft and double-chain drive have points of
advantage and of weakness, and each type has its advocates. For
the double chain, great strength can be claimed with light weight,
as the axle is in one piece, and perfectly adapted to support
the car. Against it is the difficulty of keeping the chains
properly lubricated, and their consequent wear and stretching. The
driving-shaft type has the advantage of the perfect lubrication of
the parts, for all may be inclosed and running in oil or grease; the
rear axle must be divided, however, which requires it to be heavily
braced in order that the weight imposed on it may not bend or spring
it out of line. Where a bent dead axle can be straightened by a
blacksmith, a similar condition in a live axle requires the services
of an expert mechanic; on the other hand, bevel gears make less noise
than chains.


                         DRIVING-GEAR RATIOS

Even when on the direct drive, the crank shaft makes more revolutions
than the rear wheels, in order that the momentum of the moving
parts of the engine may be sufficient to keep the car in motion. On
shaft-driven cars, the bevel on the driving shaft has fewer teeth
than that on the axle, so that it revolves more than once to one
revolution of the axle. On chain-driven cars, the driving sprockets
are smaller than those driven. This =driving-gear ratio=, as it is
called, varies from one and a half to three and a half, or, in other
words, the wheels revolve once while the driving shaft or sprocket
makes from one and a half to three and a half revolutions. Other
conditions remaining equal, a higher driving gear gives the car lower
speed, but greater ability in hill-climbing and the traversing of
heavy roads.




                              CHAPTER X

                            RUNNING GEAR


The steering of a motor car, or the change in the direction of its
movement, is effected by changing the position of its steering
wheels, usually those in front, in relation to the rear wheels. In
a horse-drawn vehicle, the axles are parallel when it is moving
straight, as are also the planes of its front and rear wheels. To
turn the vehicle to one side or the other the front axle is swung so
that it is out of parallel with the rear axles, the vehicle turning
to the side on which the axles would meet if they were extended. This
construction requires the wheels to run loose on the axle, and the
axle to be permitted to swing on the pivot by which it is attached to
the body of the vehicle.

Such a construction would be impracticable for an automobile,
because the weight resting on the front axle would require the pivot
to be of greater strength and stiffness than could be conveniently
obtained, and because of the effort that would be necessary to swing
the axle in steering. The front axle of an automobile is stationary,
and the steering effect is obtained by pivoting short pieces to its
ends, these carrying the wheels. From these pivoted ends, called
=knuckles=, extend short =steering arms=, which are connected by a
=drag link=, so that moving the drag link moves the pivoted ends of
the axle and the wheels to correspond (Fig. 44).

[Illustration: FIG. 44.—TWO ARRANGEMENTS OF THE DRAG LINK.]

[Illustration: FIG. 45.—STEERING PRINCIPLES.]

For a wheel to follow a curved path without slipping, it must be at
all times tangent to the path, and will be perpendicular to a radius
of the curve at that point. The front axle of a horse-drawn vehicle
points toward the center of the circle on which the vehicle may be
turning and forms part of the radius, the wheels, of course, being
perpendicular to it (Fig. 45). As the main part of the front axle of
an automobile is stationary, only its pivoted ends may point to the
center of the circle, and this must occur in order that the wheels
may be tangent to the curve (Fig. 45). Both axle ends point to the
center, but along different radii; if both pointed along the same
radius, it would necessitate their being in line with the stationary
part of the axle, which then also would be part of the radius. As
the axle ends are in line with different radii of the same curve, it
follows that the wheels are perpendicular to different radii, and
not parallel with each other, a condition impossible in horse-drawn
vehicles. The front wheels of an automobile are parallel with each
other when the axle ends are in line with the stationary part, but go
out of parallel as soon as they are at an angle with it, as is the
case when the car takes a curve.

If the steering arms projected from the knuckles at right angles
to the axle ends on which the wheels revolve, moving the drag link
would move each knuckle through an equal angle, and the wheels would
be parallel at all times; this is prevented by so constructing the
knuckles that the steering arms incline toward each other, with the
result that when the drag link is moved, one of the wheels swings
through a greater angle than the other, the difference between the
angle of each steering arm and the stationary part of the axle
increasing with a greater movement of the drag link.

The control of the drag link is obtained either by a =steering lever=
or =wheel=. When the steering lever is moved by the driver, the drag
link is moved to correspond by a connecting rod, and this type is
usual in small cars. It is impracticable for heavy cars because it
is =reversible=; that is, the moving of the steering wheels moves
the lever, and a firm grasp is required to prevent the shock of
striking a stone or rut from tearing the lever from the hand and
changing the course of the car. The _irreversible_ type is used for
all but the lightest cars, and while it permits the driver to change
the direction of the front wheels it prevents any movement from
being transmitted from the wheels to the steering wheel or lever.
The =screw-and-nut type= of irreversible steering mechanism (Fig.
46, _B_) consists of a heavy screw attached to the lower end of the
shaft that revolves when the driver turns the steering wheel. The
screw passes through a nut that is held in guides so that it cannot
revolve, and is therefore moved up or down when the screw is turned
by the steering wheel. From the nut extends an arm that is connected
to the drag link, so that its movement is transmitted to the wheels.
The turning of the steering wheel thus moves the nut and the front
wheels, but a movement of the front wheels from any other cause is
prevented, because no pressure on the nut can revolve the screw.
Another type is the =worm-and-worm wheel=, or =worm-and-segment=
(Fig. 46, _A_), which, while of different construction, depends on
the same principle that the movement of the worm or screw can move
a worm wheel or nut in mesh with it, but the movement cannot be
reversed.

[Illustration: _A_ _B_ FIG. 46.—STEERING MECHANISMS. _A_, Worm and
worm-wheel steering gear; _B_, nut and screw steering gear.]

The stationary part of the front axle of an automobile is usually a
forging, and must be of considerable strength in order to support the
weight imposed upon it by the engine. It is usually bent down in the
center, in order that it may be the lowest point of the mechanism,
thus to receive possible blows of stones or other high points of the
road that would cause serious damage should they strike the crank
case or fly wheel.


                               BRAKES

The brakes used in controlling the speed of an automobile may be as
many as four in number, and there should be at least two, for on them
depends the safety of the car. Brakes are of two types, =expanding=
and =contracting=, and usually operate through the friction between
a drum and a band that surrounds it, or blocks that press against
its inner surface. The =band= or =contracting= brake may be either
=single-= or =double-acting=, the latter being by far the better. In
a single-acting band brake (Fig. 47) a flexible steel band surrounds
the drum, one end being made fast to the frame of the car or some
other stationary part, and pressure applied by drawing the free end.
The friction caused by the binding of the leather or fiber lining of
the band on the drum restrains the movement if the drum is revolving
in the opposite direction to the pull, but there is little effect
if the revolution is in the same direction as the pull. In the
double-acting type, both ends of the band are pulled, and the drum
is prevented from revolving in either direction. The single-acting
type would be satisfactory when the car moves forward, but will not
hold it from running downhill backward, while the double-acting brake
holds it in either direction. The expanding brake usually consists
of two bronze =shoes=, of such shape that they fit the interior
surface of the drum. The shoes are pivoted together at one end, and
so arranged that the pull of the brake pedal or lever expands them,
binding them against the drum (Fig. 47). When pressure is not being
exerted, a coil spring, not shown in the diagram, holds them together
and out of contact with the drum.

[Illustration: _SINGLE ACTING BAND BRAKE_ _DOUBLE ACTING BAND BRAKE_
_INTERNAL EXPANDING BRAKE_ FIG. 47.—THREE VARIETIES OF BRAKES.]

Brake drums are usually attached to the spokes of the rear wheels,
and one drum often serves for both an expanding and a contracting
brake. Brake drums are also applied to the jack shaft, or to an
extension of the countershaft of the change-speed mechanism. It is
usual to have one set of brakes controlled by a foot pedal, and
another, called the =emergency brake=, by a lever at the side of
the car. The foot brake, or =running brake=, is always connected
to the clutch, so that applying it throws out the clutch. The
emergency brake is also connected in the same manner in some makes of
automobiles, but this is not recommended, for if it is necessary to
stop the car when going uphill, the brakes must be released before
the clutch can be thrown in, and the possibility of the car starting
downhill backward before power can be applied, the chance of
stalling the engine through this, and the danger of the combination
to any but an experienced driver, make it advisable to have the
emergency brake separate from any connection with the clutch.

Band brakes are usually lined with leather, to increase the friction
between the band and the drum, and this often gives rise to troubles
in the burning of the leather when the brake is applied for a
considerable period, as in the descent of a long hill. The emergency
brake has advantages in that it operates through the friction of
metal against metal, but excessive heat from continued application
may be enough to melt the metal and fuse together the shoe and drum.
For long descents, it is well to use the motor as a brake, for it
is logical to consider that the means of propulsion may also be
the means of retarding, as the wind that urges a sailboat forward
may also bring it to a stop. It is obviously impossible to reverse
the motor or gears, but by switching off the ignition circuit and
throttling down, the forward movement of the car is caused to operate
the motor, and the work necessary in driving the motor as an air
compressor is sufficient to check the speed. The effect is so great
that if the low-speed gears are engaged, the car will be brought to a
stop even on a steep hill. Another advantage of this course is that
it gives the motor an opportunity to cool, which is often necessary
after a long ascent.

In case of the failure of the brakes to operate, which may result
from poor adjustment or worn bands and shoes, the speed may be
checked by throwing out the clutch, switching off the ignition,
engaging the intermediate speed gears, and letting in the clutch very
slowly. Great care must be taken that the clutch is not permitted to
bind suddenly, for that would probably result in the stripping of the
gears. If the low-speed gears are engaged, the checking would be so
sudden, no matter how slowly the clutch might be engaged, that the
shock would probably throw the passengers from their seats.

The failure of the brakes when descending a hill produces a condition
that requires skill and coolness, and danger can only be averted by a
steady hand and a clear head.

Brakes applied to the rear wheels must have an equal grip on each,
for if one binds more tightly than the other, the car will have a
tendency to skid, or slide sideways. In the best cars this is taken
care of by an =equalizer=, in which the pull of the lever or pedal
is not applied directly to the brakes, but to the center of a bar,
each end of which is connected to one of the bands or shoes. The
lever action of this bar distributes the pull equally between the two
brakes, and unless there is a great difference in the grip on the two
drums, as might be the case if one were oily and the other dry, the
effect will be the same on both sides.


                                TIRES

For low speeds, solid tires give good results in traction and the
absorption of jolts from small obstacles, but for anything above six
or eight miles an hour, pneumatic tires are a necessity in preventing
the rapid shaking to pieces of the mechanism. A hard tire touches
the ground at but one point, and its grip on the road will be much
less than that of a pneumatic tire which, being slightly flattened
by the weight it bears, presents an oval or elliptical surface to
the road. While a pebble will force a solid tire to roll over it,
it will sink into a pneumatic tire, and the jolt that it might cause
will be entirely absorbed. Pneumatic tires are formed of alternate
layers of heavy canvaslike fabric and soft rubber, and the processes
through which they are put in manufacture are supposed to effect
their perfect combination; but as it is not the nature of rubber to
be absorbed by the fabric, the layers are only bound together by its
tenacity. The bending of the sides of the tire under the weight of
the car tends to separate these layers, and water or dirt entering
between them through cuts quickly brings ruin; it is obvious that
the less the sides bend, the smaller will be the opportunity for
the layers to work apart. A pneumatic tire should always be pumped
as hard as possible, so that it stands up practically round under
a loaded car. While the car will ride a little harder under these
conditions than when the tires are soft, there will be greater
resistance to punctures, and the life of the tires will be increased.
The normal wear to a tire should give it a smooth surface, but if it
is noticed that the tread is rough and uneven, it may be taken for
granted that the wheels do not run true. Rear wheels will be thrown
out of true by the springing or bending of the axle, and front wheels
also from this cause, but more probably from faulty adjustment of the
steering mechanism or the bending of the drag link or steering arms.

The grip of the tire on the road is much affected by the nature of
the surface, the traction on dry macadam being much greater than on
wet asphalt. When the pull of the engine on the wheel exceeds the
grip of the tire on the road, there will be a slip, and the wheel
will revolve without moving the car. This will wear the tread of
the tire far more rapidly than will ordinary running. The better
the traction of the tires on the road surface, the less will be the
tendency of the car to skid or slide sideways, and less power will
be lost through the slipping of the wheels. To reduce the chance of
slipping, because of wet asphalt or muddy roads, various devices are
in use, all of which encircle the tread of the tire, and present a
rough surface. The form in most general use consists of chains that
fit across the tread, these being detachable and used only in case of
necessity. While it is often done, it is nevertheless bad practice
to apply chains or other antiskid devices to only one of the rear
wheels instead of to both, for it increases the diameter of the wheel
and makes a difference in the resistance against the wheel, causing
the differential to operate at all times. The differential is not
constructed to operate steadily, and will wear rapidly if forced to
do so.


                               SPRINGS

[Illustration: FIG. 48.—_A_, Full elliptic spring; _B_, half elliptic
spring.]

In addition to tires, an automobile is fitted with springs, which are
necessary to absorb the shocks and jolts that are too great to be
taken up by the tires. These are usually =full= or =half elliptic=
(Fig. 48), and made of flat plates, or =leaves=, of different
lengths, the small being placed on the large, and all bound together
at the center. The combined action of the springs and tires permits
the frame and body of the car to move in a nearly straight line,
while the wheels and axles follow the inequalities of the road. When
springs break, as is frequently the case, it is from the rebound of
the body that results when the wheels drop into a deep hole, the
upward movement separating the leaves, and the entire strain coming
on the long leaves alone. To prevent this, =shock absorbers= are
recommended, which permit the springs to have a certain amount of
action, but check them if they tend to expand or compress to too
great an extent. They act either by the friction between metal plates
and washers, or by air or oil in a cylinder that permits a piston to
move freely to a certain degree, but presents resistance to a greater
motion. Shock absorbers are placed between the axles and frame, and
there should be four, two to each axle.


                            DISTANCE RODS

As the springs are placed between the axles and body and are
flexible, it is necessary to provide some method of preventing an
obstruction in the road from twisting the axle, as might result if
one wheel struck heavy sand or a stone while its mate was on good
surface. A twist of this sort would throw the axle out of line with
the drive and bind the chain or driving shaft.

[Illustration: FIG. 49.—DISTANCE OR RADIUS RODS.]

To prevent this, =radius= or =distance rods= are attached to the
axle, one on each side, extending to a point well forward on the
frame (Fig. 49). These rods are pivoted to the frame, and have a
loose joint on the axle, so that the latter is free to move up and
down, but prevented from moving forward or back. Distance rods are
adjustable, and on chain-driven cars serve to adjust the chains,
which are tightened by lengthening the rods and slackened by
shortening them.




                             CHAPTER XI

                              TROUBLES


Practice and experience are the best instructors in keeping the car
running, and the operator quickly acquires the ability to recognize
the source of trouble from the action of the engine in failing to
deliver power, or from the manner in which it stops. Each part of the
mechanism may be counted on to give trouble, and the possibilities
are numerous, but in general it may be said that an interference with
the proper operation of the engine may be laid to the failure of the
ignition system or gasoline supply, a defect of the combustion space
in not retaining the pressure, or the overheating of the engine.


                          IGNITION TROUBLES

The ignition system is the greatest producer of trouble, and the
reason is usually difficult to locate. Any interference with the
flow of the current, or leaks by which it evades passing over the
entire circuit, will cause irregular running or the stopping of the
engine, and the circuit must be maintained in the best possible
condition in order to prevent these as much as possible. The wires
should be well insulated, the insulation of the secondary circuit
being heavier than that of the primary because of the higher pressure
of the current that must be retained. The constant vibration to
which the wires are subjected requires the use of cable composed of
a number of strands of fine wire rather than a single heavy wire,
for the latter is much more liable to be broken; but in securing
the end of a cable under a nut, great care must be exercised that
all of the strands are bound. A single strand is hardly noticeable,
but if it comes into contact with uninsulated metal, it will permit
the current to leak. In making connections, the best plan is to
solder the end of the cable to a copper or brass terminal which
holds the strands secure, and gives a firm bearing for the nut.
Before making connections the terminals should be scraped bright,
and after running the nuts down firmly, covered with vaseline to
prevent corrosion. Corrosion of copper or brass produces a greenish
deposit (copper sulphate) which is an insulator, and when it forms
between the terminals of the conductor it produces high resistance,
cutting down or even preventing the flow of current. A worse effect
of corrosion is to bind the nuts on the screws, preventing their
removal. A loose connection presents resistance to the flow of
current, and the current will flow irregularly, as the vibrations
bring the terminals together or separate them. A wire broken at
a terminal is easily seen, but when a break occurs inside of the
insulation, it is more difficult to detect. When a broken wire is
suspected, its circuit may be located by testing, and new wires laid,
one length at a time, until the faulty one is replaced. It is poor
economy to use cheap wire, for the best is none too good for the hard
use to which it is put. The wearing away of insulation by chafing
will produce a short circuit, and the wires should be prevented from
coming into contact with any part of the car or engine in such a
manner as to give this result.


                             THE BATTERY

When a battery is exhausted, or nearly so, it will not magnetize the
core of the coil sufficiently to induce a current that will give a
strong enough spark to ignite the mixture. The length of time that a
battery should last, or the mileage that it should give, is learned
from experience, and when it is exhausted in less time there is
evidence that it has either been short-circuited or that the current
has been used too extravagantly.

The extra source of current that should be provided should not be
switched into circuit until the short circuit that exhausted the
regular source has been located and removed, or there will be a
further waste of current. It occasionally happens that through
carelessness the battery is so connected that one of the cells is
reversed, in which case the current will be reduced by the loss of
the current from two cells, for the energy of the reversed cell will
neutralize that of another. If both sets of battery have become
exhausted by short circuit, current for further running may be
obtained by connecting the two sets together in multiple, supposing
that each set is, as is usual, connected in series.

An apparently exhausted dry battery will recuperate, or pick up, if
allowed to stand, but a storage battery that shows 1.8 volts or less
for each cell should be immediately recharged, for further use will
cause fatal injury.


                             THE MAGNETO

The principal troubles that come to magnetos are due to lack of
lubrication and the weakening of the permanent magnets. The clearance
between the armature and the pole pieces between which it revolves is
very small, and even slight wear of the bearings through insufficient
lubrication will permit the armature to touch. The oil cups with
which the bearings are provided must be kept filled, or if the parts
are connected to a mechanical lubricator, the proper adjustment must
be maintained.

When a magnet is permitted to stand without a piece of iron
connecting the poles, the magnetism will dissipate; to prevent this,
a bar of soft iron, called a =keeper=, is placed across the poles,
the magnetic lines of force flowing through it from one pole to
the other, and the strength being retained. The permanent magnets
forming the field of a magneto are very strongly magnetized, and
the proportion of the strength lost through misuse will be large,
resulting in their being weakened to such an extent that the current
produced will not be sufficient for ignition purposes. These magnets
can be re-magnetized by the makers when this occurs, the magneto
regaining its current-producing ability.

The strength of the magnets will be retained for a much longer period
if, when the car is standing, the armature is in such a position
that it acts as a keeper; this will occur when its iron core is
horizontal. As the armature will be in this position when the current
is being produced, it is only necessary to bring the engine to a
stop at the point when one of the pistons is approaching the end of
a compression stroke. On leaving the car, the low speed should be
engaged and the clutch withdrawn; the engine may be cranked slowly,
and the armature held in position by throwing in the clutch to hold
the crank shaft when compression is nearly complete.

It is most inadvisable to take a magneto to pieces without an exact
knowledge of its construction. Except for lubricating the bearings,
it is best to leave it entirely alone. In setting a magneto, it must
be remembered that it is not delivering current continuously, and
that when the iron core of the armature is parallel to the poles
of the magnets no current is produced. The greatest strength of
current is delivered as the core moves into a vertical position, and
revolving the armature by the fingers will show this, for during
part of a revolution it will turn easily, and during the rest of the
revolution there will be resistance. The engine should be cranked
until a piston is near the top of a compression stroke; holding it
there, the magneto gear may be meshed with that on the half-time
or crank shaft in such a manner that the armature core has moved a
trifle past the vertical position. This will result in the production
of a current at the instant that it is necessary for the ignition of
the charge. (See Appendix.)


                              THE COIL

There is always a small spark between the vibrator contacts of a
coil, and in time the platinum will be burned and corroded, the oxide
that forms being an insulator and preventing the flow of the current.
In such a case the points may be smoothed with a fine flat file and
polished on a strip of leather, or if too far gone for this, may be
renewed by soldering a short length of platinum wire to the adjusting
screw and a plate of the same metal to the blade. While this job is a
delicate one, it is not beyond the range of a careful amateur.

When the insulation of the coil or condenser breaks down, as may
result from overwork or long use, it should be returned to the maker,
for the construction of a coil is exceedingly delicate, and repairs
on it require expert workmanship. It is not advisable to take the
coil apart in any way, beyond the vibrator parts, for inexperienced
handling may injure it beyond repair.


                           THE SPARK PLUG

The spark plug is a frequent source of trouble, for the insulation
may break down, or a carbon deposit may form between the points,
either fault permitting the current to pass without jumping the gap.
Plugs should be so made that when the parts are screwed together the
strain will not come against the insulation. Porcelain insulation
is brittle, and may be cracked inside the sleeve, the damage not
showing on handling and inspection, but being sufficient to permit
the spark to pass inside of the sleeve instead of between the points.
Mica insulation is usually formed of a large number of washers
squeezed together under great pressure, but the action of the heat
and the presence of oil will frequently cause the layers to separate,
permitting a short circuit.

The carbon deposit that fouls and short-circuits spark plugs
results from a rich mixture, or overlubrication, and this should be
prevented by proper adjustments. Under the intense heat the carbon
bakes hard, and can be removed only by scraping or by the action
of strong ammonia or gasoline. As in scraping the smooth surface of
the insulation may be scratched (which would give a rough surface to
which a fresh carbon deposit would cling more tightly), the removal
of the deposit by ammonia or gasoline, applied with a stiff brush, is
recommended.

The points between which the spark passes should be about one
thirty-second of an inch apart. After long use, the corrosion due to
the heat of the spark will increase this distance, when the points
should be bent together. The high compression through which the
spark is required to pass presents greater resistance than air at
atmospheric pressure, practically in proportion to the pressure,
and a current that will produce a spark outside of the cylinder may
not have sufficient pressure to give a like result when the engine
is running. If the pressure of the compression is four times that
of the atmosphere, the current should be able to produce a spark
four thirty-seconds, or one eighth, of an inch long outside of the
cylinder, and for safety this should be increased four-fold.


                             THE IGNITER

The stationary point of the igniter is carried on the end of a
screw that passes through the cylinder head or wall, and by means
of this screw its position in relation to the moving point may be
altered as desired. The distance between the points when they are
separated should be about one sixteenth of an inch; more than this
will result in the formation of a longer spark between them, and
as the passage of the spark through the high resistance of the
compressed charge will produce great heat, the igniter points will
be burned and corroded more than need be. The adjustment may be made
by loosening the lock nut on the stationary point, and running the
screw down until the stationary point is in contact with the movable
when the latter is acted on by the cam. The lock nut should be run
down until it bears lightly against the cylinder and the point then
unscrewed, the lock nut being carried with it, until the latter is
about one sixteenth of an inch away from the cylinder. This gives a
corresponding distance between the igniter points, and running the
lock nut down firmly will secure it.

The tappet spring should be of considerable strength in order to
snap the movable point from the stationary when the tappet ceases
to act. Too great strength will bring the movable point against the
stationary with such force that the platinum plate that it carries
will be battered out of place. The principal difficulty that is
encountered is the corrosion of these points, the flow of the current
being decreased or stopped by the insulating film that covers them.
The blow with which the two come together tends to knock this off and
to keep the surfaces flat, but when they become badly worn and pitted
they must be filed smooth.

The bearing in the cylinder wall in which the movable point rocks is
made after the manner of a valve; the opening must be tight in order
to prevent the leakage of compression, but sufficiently free to move
as the cam acts on the tappet. This joint cannot be lubricated with
oil because of the heat, and the two parts must therefore be kept as
smooth as possible. To attain this result they are ground together
as engine valves are ground.


                              THE TIMER

The spring that keeps the revolving part of a timer in contact with
the stationary part must be of sufficient strength to squeeze out
the vaseline with which the timer is packed, as otherwise the grease
will form an insulating film between them, preventing the flow of the
current. The timer must be securely attached to its shaft, for if it
is loose the contacts will be made at the wrong time, and the sparks
will not occur in the combustion space at the correct intervals. All
of its parts and connections should be as firm as possible. The rods
with which the stationary part is connected to the control lever on
the steering column should be provided with adjustments by which lost
motion due to wear may be taken up. There are usually several joints
in these rods, all of which may wear loose, and if there are no means
by which they may be kept tight, the lever will move a considerable
distance before the timer will respond. It is often possible to
remedy this by placing coil springs in such positions that they
take up the lost motion. A timer should be so set on the half-time
shaft that the revolving contact is just touching the stationary
contact when the piston is at its highest point in the cylinder on
the compression stroke, the control lever being in nearly its most
retarded position.

As dirt will interfere with the action of a timer, the cover should
always be in place and tightly secured.


                      THE SECONDARY DISTRIBUTER

A secondary distributer will give trouble through loose contacts,
dirt, or the splitting of the spark, the effect of the last being the
passing of the spark from the revolving part to two or more contact
points instead of but one. Particles from the carbon brush in wearing
off may stick to the insulating ring between the contacts and form a
path, or a strand of wire may project, producing the same result.


                             THE SWITCH

Loose switch parts will prevent the flow of the current or give a
vibrating contact, and should be frequently looked after. If the
switch is mounted on metal, as is occasionally the case, a loosening
of the parts or the wearing of the insulation will result in a short
circuit that is difficult to locate because the good condition of the
switch is usually taken for granted.


                          GASOLINE TROUBLES

Commercial gasoline is frequently dirty, carrying particles of matter
that will stop the fine passages and openings of the carburetor,
or containing water, the presence of which will prevent the proper
operation of the engine. Dirt may be removed by the use of a strainer
made of fine wire gauze, and water may be separated by filtering the
liquid through chamois skin, the gasoline passing through and the
water remaining. It is advisable to have a strainer and trap placed
in the piping that connects the tank with the carburetor to form the
lowest point of the system, the gasoline passing through it and
being cleansed of dirt and water.


                              THE TANK

The tank of a gravity feed system is always provided with a small
hole or vent, usually drilled through the filling cap, through
which air may enter to replace the gasoline that is drawn off in
the running of the engine. If this hole becomes plugged with dirt,
the escape of the gasoline will reduce the pressure in the tank to
such an extent that further flow will be prevented, and the engine
will stop with all of the symptoms of a lack of gasoline. On opening
the tank for the purpose of investigation, the air supply will be
renewed, and the engine will again run, to stop slowly as before.
Clearing the hole will relieve the condition. This vent may also
cause trouble in permitting water to enter and contaminate the
gasoline, this being liable to happen when the car is washed.

The pipe by which the gasoline flows from the tank to the carburetor
should project slightly above the bottom of the tank, to prevent
sediment from being drawn into it.

As gasoline rots rubber rapidly, hose should never be used to conduct
it, nor should joints be packed with rubber. Copper and brass are
attacked by gasoline less than other metals, and should always be
used in preference to iron, which is corroded by the liquid. Joints
may be made tight by the use of shellac or soap.


                           THE CARBURETOR

Besides the possibility of getting out of adjustment, the greatest
trouble with a carburetor comes from the clogging of the passages and
openings with dirt. When dirt enters, it clogs the gasoline inlet
valve and prevents it from seating properly, the float chamber being
flooded as a result. When the level in the float chamber is raised,
more than the required amount of gasoline flows out of the spray
nozzle, and the mixture that is produced is too rich. This will also
result from the bending of the valve stem or the wearing of the seat,
either of which will prevent the proper shutting-off of the flow when
the correct level in the float is reached.

A flooding float chamber may also be caused by a float that is out
of adjustment on its stem or too heavy. In the course of time the
gasoline will cut a hole through the metal of a float and leak in,
and leakage will also occur if the soldered joints open, the float
then becoming too heavy and not closing the gasoline inlet valve
at the correct time. These holes will be too small to permit the
gasoline to be poured out, but by placing the float in hot water, the
gasoline will be evaporated and driven out as a gas. In repairing a
float, as little solder as possible should be used in order that the
weight of the float may not be greatly altered. A cork float will
become soggy and heavy if the varnish coating is damaged and the
gasoline soaks in.

Carburetors are built so that the float valve and spray nozzle may
be easily cleaned, for by withdrawing plugs fine wire may be run
through them. When a carburetor is taken apart for more thorough
cleaning, the position of the gasoline and air adjustments should be
remembered, in order that they may be replaced in approximately the
correct positions, thus saving time in making the adjustments that
will be necessary.

The main air intake should be kept clean, especially when it is
covered with a wire gauze screen. Dirt will reduce the size of the
opening, and the air that enters will not be sufficient to give a
mixture of the correct proportion. The screen should be kept clean
and free from oil, for the latter is a dust collector.


                        COMPRESSION TROUBLES

A leak in the combustion space will reduce the compression by
permitting the fresh mixture to escape during the compression stroke,
and will also give an escape for the pressure resulting from the
combustion, the pressure on the piston being reduced in consequence.
The most frequent cause of leakage is worn valves, the intense heat
tending to warp the disks and to roughen their surfaces, the exhaust
valve being especially liable to this as it is surrounded by the hot
gases during the time that it is open. A badly fitting spark plug,
igniter stem, relief cock, or other opening into the combustion
space will produce the same result. Whenever possible, these parts
should be fitted with copper asbestos washers, which are soft enough
to squeeze into the inequalities of the surface, at the same time
resisting the heat and pressure.

When piston rings or cylinder walls are cut or scratched by running
without oil, the pressure will escape into the crank case, which,
while warm when the engine is running properly, will be heated to a
very noticeable degree under these circumstances. The only remedy
is the use of new piston rings and the reboring of the cylinder.
Piston rings, being of cast iron, are brittle, and must be handled
carefully. To place them in position in their grooves, thin strips
of steel, like pieces of a hack-saw blade, should be bound to the
piston, covering all but the lower groove. The ring for this groove
can then be slipped on, and when it is in position the steel strips
moved upward to expose the upper grooves, one at a time.

Piston rings are usually prevented from revolving around the piston
by pins driven into the piston between their ends; if these are not
provided, the turning of the rings will bring their ends into line,
and the pressure will leak through them. The appearance of the rings
is the best indication as to whether they are permitting leakage; if
they are tight, they will be smooth and polished all around, but if
there is leakage, they will be streaked with black carbon deposit.

Other losses of compression may be due to a cracked piston, cylinder
head or wall, the former being indicated by a hot crank case and the
latter by the presence of water in the cylinder and crank case.


                          COOLING TROUBLES

The failing of the cooling or lubrication systems will permit the
engine to heat, and if continued will produce disastrous results.
The radiator of a water-cooled engine should begin to heat shortly
after the engine has started, and will rapidly become warm all over,
thus showing that the water is circulating properly. A failure of
the circulation may be due to a clogged pump or passage, and the
cause should be located and removed without delay. Dirt in the water
is the most usual cause of the failure of the pump, and also of the
stopping of the circulation in the gravity system. A strainer should
be fitted to the filling cap of the radiator to remove bits of wood,
leaves, sand, etc. The connections of the water system are frequently
made of rubber hose, and this in rotting will free bits of rubber
that will prevent the flow. A difficulty occurring at the clamps that
attach the hose to the metal pipes is the tearing off of a strip of
the rubber lining, which closes the passage after the manner of a
valve.

The fan must be kept running correctly, and if belt-driven, the belt
must be kept tight and the pulleys free from oil that would permit
slipping.

Water that has been heated freezes much more readily than water that
has not, and therefore the water system of an automobile must be
carefully guarded against low temperatures. A freeze of the water may
crack the water jackets or split the radiator, either of which will
require the laying up of the car for repairs. The best protection is
to draw off the water if there is the slightest danger of freezing,
drain cocks being provided at the low points of the system for this
purpose. If this is not practicable, a solution of four pounds of
calcium chloride to the gallon of water, mixed hot and allowed to
cool, may be used, and it will stand a temperature of 15° F. below
zero without freezing.

The flanges or corresponding parts of an air-cooled motor should be
kept clean, for dirt will prevent the free radiation of heat.

A lack of lubricating oil, either through the failure of the supply
or the clogging of the pipes, will cause the engine to heat and the
piston to stick or seize. When the car is new, it is better to supply
too much oil than too little, but when the bearings have smoothed
down the supply may be reduced. The operation of the engine is the
only indication as to whether it is receiving a proper amount of oil,
and rather than run the risk of underlubricating the piston rings and
cylinder walls, it is better to have enough to produce a faint smoke
at the exhaust pipe. This will show that the engine is receiving a
little more than is necessary. Too much oil in the cylinder will foul
the spark plug, and as this would prevent the passing of the spark,
it is to be as much avoided as too little.

When the lubricator pipes are clogged, the easiest method of clearing
out the obstruction is to force air through them by means of a foot
pump.




                             CHAPTER XII

                          LOCATING TROUBLE


Any interference with the regular running of an automobile is usually
due to engine trouble, and the nature of the irregularity or the
unfamiliar noise will often give a clew to the experienced driver by
which the fault may be located. When the engine shows that something
is wrong, it is of little use to guess at the cause, for changing
an adjustment without being sure that it is the right thing to do
will probably add to the difficulty instead of remove it. The laying
out of a system for the location of a fault is not difficult, and
its application simplifies matters when trouble is encountered. By
following a process of elimination, the condition of the different
parts of the mechanism can be learned, and if on test the ignition
system proves to be operating correctly, the production of the
mixture may be considered to be guilty until that in turn is shown
to be innocent.


                       MAKE-AND-BREAK IGNITION

An engine equipped with the make-and-break ignition system is
always provided with a conducting bar across the top or side of the
cylinders, called a =bus bar=, connected with the source of current,
and each igniter is connected to it through a switch. If one of the
cylinders fires regularly, it is an indication that the current
is being generated properly, and that no time need be wasted in
examining the generator. By means of the switches, the igniters may
be tested individually by cranking the engine with one switch closed
and the others open. When the clutch is disengaged the engine should
run on one cylinder, and if this is the case, the igniter on the line
of the closed switch is shown to be in good condition. The opening of
this switch and the closing of the next will give a comparison when
the engine is again cranked, and if explosions occur, the igniter
points may be adjusted until the two cylinders work equally well.
If the cylinder does not operate, the stationary igniter point
should be withdrawn and its contact examined; this should be bright
and clean. The movable point should be worked by hand, to determine
whether the joint is stuck or the spring weak or broken.

If none of the cylinders show signs of explosions, the connections
should be examined to make sure that they are secure. On systems
employing a magneto alone, the wiring consists of a single wire
from the magneto to the bus bar, and the shorter wires from there
to the igniters. These wires are clearly visible, and any loose
connections or broken wires may be detected without difficulty. If
the connections and wiring are in good condition, the fault may be
located in the magneto, or, if it has recently been dismounted, its
incorrect setting in relation to the crank shaft. (See Appendix.)

If the ignition system proves to be in proper working order,
attention may be paid to the carburetor and its connections.


                         JUMP-SPARK IGNITION

In testing an engine fitted with the jump-spark ignition system,
the circuit should be closed and the crank shaft revolved
twice, attention being paid to the sound of the vibrators. On
a four-cylinder engine, the timer makes four contacts in two
revolutions of the crank shaft, and if all of the vibrators are
heard it is proof that the primary circuit is in good condition, and
not the seat of the trouble. If only one of the vibrators buzzes,
the battery circuit may be considered to be working properly, for
otherwise no current could have passed to the coil box. The trouble
may then be identified as being in part if not altogether in the
adjustment of the vibrators of the dead coils, their connections
with the timer, or in the timer itself. One end of a short piece of
wire should be touched to the timer binding post of one of the dead
coils, and the other to any metal part of the engine, the lubricator,
for instance, to form a short circuit through the primary circuit
with the exception of the timer and its connections. If the vibrator
buzzes, the trouble is not in the coil, but in that part of the
circuit cut out by the short-circuiting wire. The same piece of wire
may be used to bridge across to any metal part of the engine from
the binding post on the timer at which the wire from the coil is
connected, and if the wire from the coil to the timer is in good
condition, the vibrator will again buzz, showing that the fault must
be in the timer, for all other parts of the primary circuit of that
particular coil have been proven to be working correctly. A dirty or
faulty contact in the timer, or a loose connection, will probably be
the cause.

If the primary circuit is shown to be in good order, attention may at
once be given to the gasoline feed, for while the secondary circuits
have not been tested, it is extremely unlikely that the spark plugs
or their connections will prove defective on all four cylinders at
the same time.


                           THE CARBURETOR

Touching the primer of the carburetor will show whether the gasoline
flows to the float chamber, for if it is present it will spurt out of
the opening through which the priming stem passes. If the air inlet
is so arranged as to permit it, gasoline dropping out of it when the
carburetor is primed excessively indicates that the liquid flows out
of the spray nozzle, this part thus being shown to be clear. If no
gasoline shows around the priming stem, the feed pipe or float valve
may be suspected of being clogged, it being taken for granted that
there is gasoline in the tank and that the supply cock is open. If
it is found that gasoline is present in the air inlet, and that the
carburetor is damp with it when the primer has not been touched, it
indicates that the float chamber is flooded; the carburetor should be
taken apart for inspection and thorough cleaning.


                        ENGINE WILL NOT START

When the engine will not start on cranking it eight times or so,
it is useless to continue to crank it, for there is every reason
to believe that something is wrong. Too often the difficulty is in
forgetting to switch on the ignition circuit or to open the gasoline
feed. Cranking the engine slowly will not reduce the pressure in the
inlet pipe sufficiently to draw out of the spray nozzle the quantity
of gasoline required to form an inflammable mixture; quick cranking
is necessary. Too much priming will result in the formation of a
rich mixture; the gasoline should be permitted to evaporate, or the
carburetor drained, and then primed gently.

The failure of an engine to start on a cold day may be due to the
slowness with which gasoline evaporates when chilled. As it is
obviously most unwise to heat the carburetor with a flame, the best
thing to do in such a case is to pack it with cloths soaked with hot
water. A little gasoline squirted into the air inlet, or cotton waste
soaked with gasoline and held over the same opening, will almost
always permit the engine to be started; another method is to squirt a
few drops of gasoline into the cylinders through the relief cocks.


                 ENGINE DOES NOT DELIVER FULL POWER

Regularly occurring explosions indicate that the cylinders are
receiving the proper quantity of mixture, and that the ignition is
operating correctly. If under these conditions the engine fails to
deliver full power, which is shown by the sluggish running of the
car, the trouble may be identified as the result of a condition by
which power is absorbed between the engine and wheels. This may be
from a slipping clutch, binding brakes, or tight bearings, these more
probably on the wheels than on the change-speed mechanism or drive.

The brake rods may get out of adjustment, or the spring stick, with
the result that the bands or shoes are in continual contact with
the drums. A simple test for the condition of the brakes is to push
the car across the floor by hand; it is not difficult to recognize
unusual stiffness. This test also applies to the wheel bearings.
Engine or transmission bearings that are too tight will heat, and
a touch of the hand will show the presence of this condition. A
tight bearing should be permitted to cool before readjusting it and
proceeding.


                           WEAK EXPLOSIONS

Regular but weak explosions may be due to too rich or too poor a
mixture, or to the escape of compression. Cranking the engine twice
will produce a compression stroke in each of the four cylinders, and
if there is a leak, the ease with which the piston in which it occurs
may be pulled over dead center will show its presence. A little
soapy water around the spark plug, relief cock, or other opening
into the combustion space will show the escape of compression in
the formation of bubbles. A hiss inside of the cylinder indicates a
leaky piston ring, or that the openings of the rings are in line, and
when this sound is sharp and clear, the presence of a broken ring.
An additional proof of this is the undue heating of the crank case.
If the compression is correct, the carburetor may be readjusted to
improve the quality of the mixture. A poor mixture may be due to the
partial clogging of the spray nozzle or its passages, and a rich
mixture to the choking of the air inlet by dirt or dust, this being
especially liable to occur when the part is oily.


                         MISSING EXPLOSIONS

The missing of explosions is a common failing of automobile engines,
and while it may be due to a variety of causes, the most usual is
that the spark does not pass. It is not always an easy matter to
determine which of the cylinders is missing; if the missing is
constant, the coolness of the exhaust pipe of one as compared to
the others locates the fault. If the missing is not constant, the
difference in temperature will not be noticeable, but the one at
fault may be located by holding down all of the vibrators but one.
If the cylinder corresponding to the free vibrator runs steadily,
its vibrator may be held down and another released, this being
continued until the faulty cylinder is located. The condition
of the secondary circuit of this cylinder may be ascertained by
disconnecting the secondary wire from the plug, and holding it about
a half inch away from the plug terminal while the engine is cranked.
If no spark passes when the timer makes contact, the trouble is in
either the wire or the coil; if a spark shows, it should be of good
strength, for a current that will produce a fair spark in the open
may not have sufficient strength to produce a like result when under
compression. If a good spark shows, the spark plug may be suspected
of being fouled and thus short-circuited, of having a breakdown in
its insulation, or of there being too great a distance between its
points. The threads wear a little each time that a spark plug is
removed from the cylinder, and in order to retain a gas-tight joint
it is best not to unscrew the plug unless it is necessary.

If the secondary circuit is proven to be in good condition, attention
should be paid to the carburetor, for a poor mixture, or water
in the gasoline, will cause the engine to miss. A badly fitting
exhaust valve will permit the burned gases to be drawn back into the
cylinder, the fresh charge thus being weakened, and as the valve will
shift around on its seat, this may happen irregularly. Missing will
also be caused by a weak or broken inlet-valve spring, or by the
sticking of the inlet valve, these conditions resulting in failure
to retain the mixture in the combustion space during the compression
stroke. This pushing back into the inlet pipe of the charge will
usually produce a popping or gurgling noise that is easily recognized.


                        MISSING AT HIGH SPEED

If an engine runs well at low speed, but misses when speeded up, the
trouble may be due to weak battery, stuck vibrator blade, or loose
connections. A battery that will produce a good spark at low engine
speed may not be able to respond to the greatly increased demands
of high speed, and similarly, at low speed the period during which
the timer holds the circuit closed is longer than at high speed, and
the vibrator has more time to get into action before the circuit is
broken. A loose connection may be so shaken by the vibrations of high
speed as to break the circuit.


               ENGINE STARTS WELL, BUT COMES TO A STOP

If the battery is nearly exhausted, it will recuperate during a
rest to such an extent that it will produce good sparks, but as
its condition of strength is only temporary, the engine will slow
down and come to a stop as the current fails. This action of the
engine may also be due to carburetor defects by which the vibrations
of running either cause the flooding of the float chamber or the
clogging of the spray nozzle, the mixture in both cases becoming
noninflammable; the condition will also result from an air-bound
supply tank.


                             OVERHEATING

It sometimes happens that the engine will continue to run after the
ignition circuit is opened. This may be due to a failure of the
water circulation, which is indicated by the low temperature of the
radiator, or by the low speed or stopping of the fan from a slipping
or broken belt. If the cooling system is working properly, the
lubrication must be investigated. If the oil is flowing as it should,
the cause will be found in the formation of a carbon deposit in the
combustion space, fine points of which will become incandescent
and ignite the mixture as it passes into the cylinder or as it is
compressed. A more unlikely fault may be that the points of the spark
plug are fine enough to become heated in a similar manner; modern
plugs are made with points of such size that this possibility need
hardly be considered. This ignition of the mixture by other cause
than the proper spark is termed =preignition=.


                       ENGINE COMES TO A STOP

If the engine stops suddenly, the fault will be found in the
accidental opening of the switch, or the breaking of a wire or
connection. An abrupt stop cannot be caused by anything but an
interruption of the ignition circuit, for the cessation of the
gasoline feed will bring the engine to a stop slowly, the gasoline
in the float chamber and spray nozzle being sufficient to permit
weakened explosions before the supply entirely fails. A slow stopping
of the engine from causes other than those previously mentioned may
be laid to defective gasoline feed, the emptying of the tank, the
clogging of the supply pipe, float valve, or spray nozzle, or the
closing of the supply cock from jolts and vibrations.

If the engine comes to a stop when there appears to be no fault with
the explosions, the cooling or lubricating systems may be at fault,
resulting in the heating of the cylinder to such an extent that the
piston sticks or seizes. Excessive heat is proof of this, the burning
or “frying” of excess oil on the outside of the cylinder being an
early warning. A seized piston may be freed by injecting kerosene
into the cylinder, and cranking, the cylinder first being given time
to cool.


                               NOISES

The noises made by the engine when operating properly become so
familiar to the careful automobilist that any other sound is
recognized more by instinct than by attention. Faults will often make
themselves known by noises, and these may be broadly classified as
pounds or knocks, hisses, squeaks, and rattles. A pound that occurs
regularly may be due to a loose connecting rod or wrist-pin bearing,
and in this case will be heard once to every two revolutions of the
crank shaft. A pound that occurs oftener than this may be set down
as a loose crank-shaft bearing, or a loose or cracked fly wheel. If
often happens that a fly wheel in this condition =will= make itself
heard, while sufficiently tight to show no sign of the defect on
casual inspection.

A hard metallic pound is caused by the combustion of the charge
before the completion of the compression stroke; this condition may
result from preignition or from the spark being too far advanced. If
the latter is the case, retarding the spark will stop the pounding.

Hisses are due to leaks in the combustion space, as already described.

Squeaks indicate a dry bearing, or a lack of lubrication in one of
the moving parts. The bearing may be detected by its heat. A squeak
of the leaves of a spring will often be difficult to trace and
locate, because of its irregularity.

Rattles indicate that something is loose, and should be located
without loss of time. All nuts and bolts should not only be tight,
but in addition secured in position by the use of lock nuts or cotter
pins.

Backfiring, which is an explosion of the mixture in the inlet pipe
or carburetor, may be due to a stuck inlet valve that permits flame
to pass and ignite the mixture before it reaches the combustion
space, but more probably either to ignition occurring so late that
combustion is still occurring when the inlet valve opens, or to
preignition.

Explosions in the exhaust pipe or muffler are due to the presence
of unburned mixture, which is passed out of the exhaust valve after
ignition has failed, and ignited by the heat of the exhaust pipe, or
by the hot gases from the next explosion.




                            CHAPTER XIII

                    MAINTENANCE AND CONSTRUCTION


In order that an automobile may be maintained at its highest
efficiency, a constant watch must be kept over all of its parts, and
repairs and replacements made as soon as the necessity is apparent.
A worn bearing or loose part may continue to operate, but the wear
will be far greater than would occur under normal conditions, and may
result in serious breakage. A system of inspection to be gone through
every time that the car is used will keep the driver informed as to
its condition, and it is best to form the habit of doing this at the
end of a run rather than before, for then the necessity for making
readjustments or repairs will be fresh on the mind.


                             INSPECTION

The condition of the ignition circuit and of the compression will
be shown in revolving the crank shaft twice, and the action of the
carburetor may be ascertained at the same time. Pushing the car
across the floor will show the presence of tight brakes or wheel
bearings, and the tires may then be examined for cuts. Beginning at
the front of the car, every bearing not fed by the lubricator should
be oiled, and all grease cups given a slight turn, those that are
empty or nearly so being filled. While this is being done, a watch
may be kept for nuts and bolts that may have been loosened by the
vibrations.


                               WASHING

The car should be washed with clear, cold water only, and mud floated
off; to remove mud by rubbing or any other method than sluicing it
away by the action of a gentle stream of water will scratch the
varnish and ruin the appearance of the car. When clean, the varnished
parts may be dried with chamois or wash leather, and the finish
retained by a light coating of a good furniture polish, which is to
be immediately dried by rubbing.

The tires may be cleaned by sponging, but water should not be
allowed to settle in the bead. On cars having the gravity system of
gasoline feed, the water should not be permitted to splash on the
tank, for it will enter through the vent. Water should also be kept
from the upholstery, for if it enters the folds and buttonholes it
will cause rotting.


                              THE TIRES

Light and heat are the worst enemies of rubber; spare tires should
be kept in a cool, dark place, and protected from dust and moisture.
French chalk, or some similar preparation, should be well dusted
over the shoes and tubes, and if the tubes are folded, they should
occasionally be opened and refolded in fresh places, to prevent the
formation of creases. The spare tire that is carried on the car
should be kept in a casing, and because a dark surface will absorb
more heat than a light, the casing should be tan, gray, or white
rather than black. The casing should be as proof as possible against
moisture, but for safety should occasionally be removed and aired.
The position of the shoe in the holders should be changed every
little while, in order that the straps may not cut into the bead.

The tires on the wheels should receive care, and when the car is left
standing, it should be in the shade whenever possible, to protect
them from the deleterious action of the sunlight in hardening the
rubber. They should frequently be examined, and any cuts filled
with strong cement, for otherwise water and sand will work in to
form blisters and to separate the layers of fabric from the rubber.
The cutting of tires can be reduced by withdrawing the clutch when
crossing broken stones, the car coasting over them; driving the car
over such a surface will force the tires against the sharp edges, and
cutting will result more surely than when the tire rolls over them.


                         CARE OF THE ENGINE

The carbon deposits that will form in the combustion space will in
time tend to stick the piston rings in their grooves, and this may be
prevented by squirting a few drops of kerosene oil into the cylinders
and cranking the engine to distribute it. This should be done at the
end of a run, and the engine permitted to stand in that condition.
The first explosions will vaporize the kerosene and drive it off
unless too much has been used, when there will be a tendency to foul
the spark plugs.

The lubricating oil should be drained out of the crank case every
five hundred miles, and the case washed out with kerosene before
refilling it with fresh oil. Gasoline has too great a cutting
action to warrant its use for this, as it cleans down to the bare
metal, while kerosene removes the dirt and grease, leaving a good
surface. The case should be filled with oil to such a depth that the
connecting rods will dip into it from a half-inch to an inch.

The same should be done with the change-speed gear case every
thousand to fifteen hundred miles, for the particles of metal that
will be ground from the gears will injure the teeth and bearings.
In refilling, the smallest gear should project about an inch into
the oil. If the differential is packed in grease, it will run for an
entire season with one filling, but if it runs in oil it should be
cleaned and washed two or three times a year. The bevel gear case of
a shaft-driven car should receive the same attention.


                           CARE OF CHAINS

Properly lubricated chains should run for at least a thousand miles
without attention. Because of their exposed position they should be
protected against undue wear, and this is best attained by soaking
them, when thoroughly cleaned, in melted tallow, working each joint
in order that the liquid may penetrate. The chain should be hung up
to cool and dry, the surplus tallow being wiped off. The hardened
tallow in the joints will prevent grit from working in, and is a
lubricant as well. To clean a chain, soak it in kerosene, working
each joint to remove the grit. The stretching of the chain may be
taken up by lengthening the radius rods, but when the stretching
reaches a point that permits it, the chain should be shortened by
the removal of a link, and the rods readjusted. If a complete chain
is not carried as a spare part, the kit should always include a few
extra links for emergency repairs. These are not difficult to apply,
being secured in position by nuts instead of by burring over the
ends of the rivets.


                           VALVE GRINDING

To grind a pitted or worn mechanically operated valve, the pressure
should be released by compressing the spring and removing the key
or other device by which it is held in place. On removing the plug
over the valve pocket, the upper surface of the valve disk will be
exposed, and it will be found to be provided with a slot. While many
grinding pastes may be purchased, good results will be obtained by
mixing machine oil with flour of emery until it is thick. Plugging
the opening from the valve pocket to the combustion space with cotton
waste to prevent the paste from entering the cylinder, spread it
on the valve disk and seat, and rotate the disk on its seat with a
screwdriver, preferably by means of a bit brace. Every little while
the disk should be lifted and replaced on the seat in a new position,
in order to distribute the wear evenly, and the grinding continued
until a smooth surface shows all around both disk and seat. It is not
necessary to smooth the entire surface of the disk and seat, for the
pressure will be retained by a narrower surface.

An automatic valve may be removed from the cylinder by unscrewing or
unbolting its cage, and after releasing the spring the cage may be
held in a vise while the grinding is performed.

After grinding, all traces of the paste should be removed by washing
with gasoline, for any particles that remain will cause rapid wear.
When replacing the spring, that of the mechanically operated valve
will be found difficult to compress to the point at which the key
or washer may be slipped into position, and to simplify this many
engines are built with a knob or boss on the cylinder to serve as
a fulcrum by which a forked lever may be used. If this is not the
case, the spring may be sufficiently compressed in a vise, and bound
endwise with wire to retain it, the wire being cut when the spring
and key are in position.


                     CARE OF STEERING MECHANISM

A failure of the steering mechanism will cause a wreck more surely
and quickly than the breakdown of any other part of the car, and
the best protection is absolute knowledge that it is in perfect
condition. All joints should be kept well lubricated, and protected
from dust; the leather protectors that are furnished do not
accomplish this any too well, but they are much better than nothing,
and if the joints are packed with grease before applying them, the
results will be good. While guarding against stiffness, there should
be very little play or lost motion in the mechanism, and the parts
should be frequently examined for bent rods and loose joints. A bend
in the drag link or steering knuckles will throw the front wheels
out of true, in which case the tires will be badly worn. When going
straight ahead, the wheels should be parallel; if this is the case,
the angles of the steering arms will give the proper track when
making a turn.


                           CARE OF SPRINGS

The springs of an automobile are in constant motion, and should be as
carefully lubricated as the other parts of a car. The spring hangers
by which the two halves of a full elliptic spring are joined, or
by which a half elliptic spring is attached to the frame, are often
provided with grease cups, but in the absence of these the parts
should be frequently oiled. Once a season fresh lubricant should be
applied to them. The leaves of a spring may usually be separated
enough for this by jacking up the body, applying the jack to the
frame; the springs will thus be relieved of the weight, and the
leaves will separate sufficiently to permit heavy grease or graphite
to be introduced between them by means of a table knife. If the
springs are too heavy to permit this, they must be taken apart, which
may be done by removing them from the car and releasing the clips by
which they are held together. In reassembling a spring, it may be
clamped in a vise, when the clip may easily be secured.


                         ADJUSTING VIBRATORS

In adjusting the vibrators, the best guide is the running of
the engine. The musical tone that they make is misleading, for
a difference in the steel of which the blades are made, or in
the quality of the core, will produce a difference in the tone,
and because two vibrators sound alike is not proof that they are
producing equal secondary sparks. With a one-cylinder engine, the
adjusting screw may be turned until the engine is running at its
best, while at the same time there is the smallest spark between the
vibrator contacts. The adjustment of the vibrators of a multicylinder
engine is proceeded with along similar lines, all of the blades but
one being held down, while the free blade is adjusted until the best
results are obtained in the operation of the cylinder to which it
corresponds, and the smallness of the spark between the vibrator
contacts. When one is correct, it is held down and another released,
this process being continued until all are adjusted.


                           MATCHING COILS

When coil boxes are so built that the units may be removed
conveniently, as is usually the case, it often happens that the
running of an engine may be improved by matching the coils and
cylinders. A difference in the compression in one cylinder will
often cause it to run better on one coil than on another, for no two
coils will give identical results. Taking each cylinder in turn, and
transposing the coil units in the box, the effect of each coil may be
noted, and a combination found that will improve the operation of the
engine.


                      ADJUSTING THE CARBURETOR

When adjusting a carburetor, it must be remembered that the
proportion of liquid gasoline to air in a correct mixture is very
small; because this is not well understood, a rich mixture is present
far more commonly than a poor one. To begin at the beginning, close
both the gasoline and auxiliary air inlets, and opening the gasoline
adjustment a very little at a time, crank the engine with the relief
cocks open until combustion is secured, the spark being retarded and
the throttle nearly closed. When the engine runs, note the color of
the flame that shoots out of the relief cocks. A poor mixture will
produce a yellow flame, and a rich mixture a red and smoky flame,
with black smoke at the exhaust and a smell of gasoline. The flame of
a correct mixture is blue and hardly visible. On securing a correct
mixture at low speed, advance the spark and open the throttle to
speed up the engine, and the mixture will at once become too rich.
Adjusting the auxiliary air inlet by weakening the tension of its
spring will bring the mixture to approximately correct proportions.
A more careful adjustment under road conditions can be obtained by
adjusting the air inlet while the car is being operated, for the
position of the carburetor is usually such that this may be done
while standing or kneeling on the running board.

Faulty adjustment of the carburetor is often suspected when the real
source is in the throttle or governor connections. The bending of a
rod connecting the throttle with either the foot, hand, or governor
control, or the wear of the joints, will throw the carburetor out,
and the possible failure of these parts must be borne in mind
accordingly.


                         SETTING THE VALVES

In setting or timing the valves of a gasoline engine, the point to
be considered is the closing of the exhaust valve, for upon this
good results depend. If this valve is held open too long, the
burned gases driven out will be drawn back into the cylinder, and if
it closes too soon the greatest possible quantity of burned gases
will not have been expelled. The many experiments carried on by the
manufacturers, and the attention that they must pay to this point,
result in the delivery of cars with valves correctly timed, and
usually with marks made on the two-to-one gears to guide in resetting
them. In the absence of these guides, the setting of valves need
not be difficult, although experimenting is required to secure the
best results. The first step is to locate the position of the piston
in the cylinder. There is always an opening in the cylinder head—a
relief valve, the spark-plug opening, or other—and a stiff wire may
be dropped through it, with its lower end resting on the piston and
its upper end projecting. As the piston is moved by cranking the
engine, the wire will move with it, and is to be marked with a file
at its highest and lowest positions. While no fixed rule can be
laid down, it may be said that in general the exhaust valve should
close when the piston has made from 1/64 to 1/32 inch of its outward
stroke. The two-to-one gears having been unmeshed, the cam shaft
may be revolved in its bearings by hand; cranking slowly, move the
piston down from its highest point to that at which the exhaust
should close, and hold it there. Revolve the cam shaft until the nose
of the cam is passing from under the roller of the valve-lifter rod,
and the valve just closed. This point may be accurately ascertained
by placing a strip of thin paper between the valve-lifter rod and
valve stem; when the cam is acting on the valve-lifter rod, the
paper will be pinched, but the seating of the valve will release
it. When the paper can be pulled out, mesh the two-to-one gears,
and the relations thus established between the crank and the cam
shafts will be maintained. Cranking the engine a few times, using
the strip of paper, will verify results, and the engine may then be
started and the effect noted. If the running is not satisfactory,
unmesh the gears, and mesh them with a difference of one tooth, first
one way and then the other, noting results, and retaining the most
satisfactory position. Cams are often cut in one piece with the cam
shaft, and the gear keyed on the end; there is therefore no chance
to make a finer adjustment than what is permitted by shifting the
gears one tooth at a time. On multicylinder engines, one cam shaft
operates all of the exhaust valves, and the setting of one valve sets
all.

When inlet valves are of the mechanically operated type, but
controlled by a separate cam shaft, this must be set in a similar
manner. The nose of the cam should just be coming into contact
with the push rod roller at the instant when the exhaust valve is
completely closed. This should occur as the piston begins to move
outward on the inlet stroke, the exact position being determined by
experiment.

When the cams are so badly worn that if they are set to open
correctly they close too soon, the best remedy is a set of new cams;
for while the brazing of a strip of brass to the sides of the cams
can be resorted to, the result is only temporary at best, and not as
accurate as that secured by the use of new cams.

While the tension of the spring of an automatic valve is sometimes
controlled by a nut, its adjustment usually depends on the stretching
of the spring to strengthen it, or the cutting off of part of a turn
to weaken it. The tension should be adjusted, one cylinder at a time,
until the best results from each are secured.


                             THE WIRING

[Illustration: FIG. 50.—JUMP SPARK WIRING DIAGRAMS.]

In laying the wires for the ignition system, only the best wire
should be used, and all contacts should be bright and clean.
Connections should be tight, and covered with vaseline to prevent
corrosion, additional protection being secured by binding all exposed
places with so-called electric tape. There should be the fullest
protection against chafing and moisture, and no sagging of the wires.
Beginning with the battery, the cells should be placed in a box that
holds them securely, so that there may be no jolting, for this in
working the wires will tend to loosen the connections. In connecting
the cells, the wires should be cut to correct length, but not so
short that they will be drawn tight when connected. The insulation
should be cut off cleanly, and the paraffin that will cling to the
metal scraped off. The ground wire may then be run, after which the
wires from the two batteries may be connected to the switch. (Fig.
50). On multicylinder engines, one circuit should be completed and
tested before another is started, as this obviates the danger of
confusing the wires. The primary wire should be run from a coil unit
to its timer contact, making sure by the buzzing of the vibrator that
the current flows when the switch is closed. A buzz of the vibrator
when the timer is not making contact indicates a short circuit. The
primary circuit for the coil having been correctly arranged, the
secondary connection should be made and tested before laying the
primary of the next coil unit. In making the timer contacts of a
four-cylinder engine the firing order as established by the opening
of the exhaust valves must be kept in mind. With the spark control
lever in the retarded position, the timer should be set so that it is
just beginning to make a contact when the piston in cylinder No. 1
is at top dead center of the compression stroke. This contact should
then be connected to the primary terminal of the first coil, and the
secondary of that coil connected to the spark plug. If the firing
order is 1, 2, 4, 3, (Fig. 51), cylinder No. 2 will be the next to
fire, and the primary of coil 2 should be connected to the next
timer contact in the direction of rotation. As the next cylinder
to fire will be No. 4, the timer contact that will next be reached
should be connected to coil No. 4, the remaining contact point being
connected to coil No. 2. In the diagram the timer is supposed to be
moving in the same direction as the hands of a watch.

[Illustration: FIG. 51.—JUMP SPARK WIRING DIAGRAMS.]

There is no difference in the wiring of a horizontal double-opposed
and a two-cylinder vertical 180° crank-shaft engine, as shown in Fig.
50, except that the timers are so built that in the first the two
contacts are a quarter revolution apart, and in the second a half
revolution.

In wiring a car with a single coil and secondary distributer the four
contacts of the timer all lead to the primary terminal of the coil,
the firing order being according to the manner in which the secondary
terminals of the distributer are connected to the cylinders (Fig. 51).

Wiring for the make-and-break system is much simpler than that of the
jump-spark, and when a magneto alone is used, it consists, as will be
seen from Fig. 52, of only a wire from the magneto to the igniters,
the other terminal of the magneto being attached to its metal base
in such a manner that the ground connection is made when the magneto
is secured in position on the engine. The firing order is according
to the setting of the cams that operate the igniter tappets.

[Illustration: FIG. 52.—MAKE-AND-BREAK WIRING DIAGRAM. Magneto and
coil. Battery for starting.]

[Illustration: FIG. 53.—MAKE-AND-BREAK WIRING DIAGRAM. Magneto
ignition without coil. Starting on magneto.]

                          =LUBRICATION TABLE.=

                      PART.                 LUBRICANT.        QUANTITY.
  —————————————+————————————————————————+—————————————————+———————————————
               | Engine cylinder        | Cylinder oil    | 6-12 drops per
               |                        |                 |  minute.
               | Engine bearings        | Cylinder oil    | 8 drops per
               |                        |                 |  minute.
  =Require=    | Fan bearings           | Cylinder oil    | 1 drop every 2
   =constant=  |                        |                 |  minutes.
   =attention.=| Magneto, plain bearing | Cylinder oil    | Keep pockets ⅔
               |                        |                 |  full. Wash
               |                        |                 |  out with
               |                        |                 |  kerosene once
               |                        |                 |  a season.
               | Clutch leather         | (Vegetable),    | If clutch
               |                        |   castor oil,   |  slips or
               |                        |   neatsfoot oil |  leather
               |                        |                 |  gets hard,
               |                        |                 |  keep off
               |                        |                 |  machine oil.
  —————————————+————————————————————————+—————————————————+———————————————
               | Valve lifters          | Cylinder oil    | With oil-can.
               | Timer-shaft            | Cylinder oil    | With oil-can.
               | Pump shaft drive       | Cylinder oil    | With oil-can.
               | Magneto drive          | Cylinder oil    | With oil-can.
               | Lubricator shaft       | Cylinder oil    | With oil-can.
  =Require=    | Clutch release         | Cylinder oil    | With oil-can.
   =attention= | Lever bearing          | Cylinder oil    | With oil-can.
   =daily.=    | Steering knuckle       | Grease          | One turn.
               | Water pump             | Grease          | One turn.
               | Clutch-shifting collar | Grease          | One turn.
               | Transmission bearings  | Grease          | Two turns.
               | Outer bearing live     | Grease or oil   | Two turns.
               |   rear axle            |                 |
  —————————————+————————————————————————+—————————————————+———————————————
               | Starting-crank bracket | Cylinder oil    | Few drops.
               | Spring shackles        | Cylinder oil    | Few drops.
               | Make and break tappets | Cylinder oil    | Few drops.
               | Pedal-shaft brackets   | Cylinder oil    | Few drops.
               | Speed-change lever     | Cylinder oil    | Few drops.
               | Emergency lever        | Cylinder oil    | Few drops.
  =Require=    | Brake supports         | Cylinder oil    | Few drops.
   attention=  | Brake equalizers       | Cylinder oil    | Few drops.
   =weekly.=   | Control levers and     | Cylinder oil    | Few drops.
               |  joints                |                 |
               | Spring hangers         | Cylinder oil    | Few drops.
               | Clutch; multiple disk, | Spindle oil and |
               |  steel on steel        |  kerosene,      |
               |                        |  or kerosene and|
               |                        |  little graphite|
               | Clutch; multiple disk, | No oil, little  |
               |   leather on steel     |  graphite       |
               | Internal expanding     | Thin oil        |
               |   clutch               |                 |

               |        PART.        |     LUBRICANT.     |   QUANTITY.
               |                     |                    |
               | Engine crank case.  | Cylinder oil.      |
               | Steering gear case. | Grease.            | 3 turns or
               |                     |                    |  gunful.
               | Transmission-case,  | Gear case          |
               |  sliding            |  compound or heavy |
               |  gear system.       |  oils, or either   |
  =Require=    |                     |  mixed with about  |
   =attention= |                     |  ten per cent. of  |
   =every two= |                     |  graphite.         | Let gears dip.
   =weeks or=  | Transmission case,  | Light motor oil and|
   =every 300= |  individual         |  little graphite.  |
   =miles.=    |  clutch type.       |                    |
               | Planetary           | Non-fluid oil, or  | Fill up no
               |  transmissions.     |  oil and graphite. |  higher than
               |                     |                    |  shaft
               |                     |                    |  bearing.
               | Live rear axle      | Non-fluid oil or   |
               |                     |  heavy steam engine|
               |  housing.           |  cylinder oil;     |
               |                     |  grease            |
               |                     |   and oil.         | One quart.
  —————————————+—————————————————————+————————————————————+———————————————
               | Magneto, ball       |                    |
               |  bearing.           | Cylinder oil.      | Small amount.
               | Front and rear      |                    |
               |  wheel-hubs; ball   |                    |
               |  or roller bearing. | Grease.            |
  =Require=    | Front and rear      |                    |
   =attention= |  wheel-hubs;        |                    |
   =monthly=   |  plain bearing.     | Graphite and oil.  |
   =or every=  | Leather boots of    |                    |
   =500 miles.=|  steer-rod joints   |                    |
               |   and steer         |                    |
               |   drag-rod joints.  | Grease.            |
               | Universal joints.   | Grease.            | Remove
               |                     |                    |   covering,
               |                     |                    |  inspect and
               |                     |                    |  repack.
               | Torsion and         |                    |
               |  distance rods.     | Oil.               |
               | Timing gears.       | Non-fluid oil;     |
               |                     |  graphite if       |
               |                     |   exposed.         |
  —————————————+—————————————————————+————————————————————+———————————————
               | Friction disk       | Keep oil off       |
               |  transmission.      |  friction surfaces,| Renew friction
  =Require=    |                     |  wash off with     |  compost every
   =attention= |                     |  gasoline, dress   |  1,000 miles.
   =at greater=|                     |  with belt dressing|
   =periods.=  |                     |  or French chalk.  |
               | Chains.             | Chain graphite.    | Twice a year
               |                     |                    |  boil in
               |                     |                    |  graphite and
               |                     |                    |  grease after
               |                     |                    |  washing well
               |                     |                    |  in kerosene.




                              APPENDIX




   OPERATION AND CARE OF LOW AND HIGH TENSION MAGNETOS AND MAGNETO
                          IGNITION SYSTEMS


                         GENERAL PRINCIPLES

The red-painted toy magnet that is one of the properties of childhood
and with which everyone is familiar, may well be used as the
beginning of a study of the magneto, for with it the characteristics
of magnetism may be observed. A little experimenting will show that
the magnet will attract, or “pick up”, iron and steel objects only,
having no effect on copper, brass, lead, wood, or, for practical
purposes, any other substance. Furthermore, it illustrates the fact
that when iron and steel are in contact with it, they in turn become
magnetic, able also to attract tacks and other bits of the same
metals. Iron, however, is shown by experiment to be magnetic only
when in actual contact with the magnet, losing its magnetism as soon
as the contact is broken, while when steel is magnetized by touching
it to a magnet it remains magnetic. This fact is illustrated by the
magnet itself, which is of steel and therefore capable of retaining
its power for a greater or less time, depending on its quality and
hardness.

[Illustration: FIG. 1. MAGNETIC LINES OF FORCE.]

If iron filings are scattered on a piece of paper laid over a magnet
they will not fall evenly and regularly, but will collect most
thickly at the ends, or poles, of the magnet, showing that there the
magnetic attraction is stronger than at any other points. If the
filings are examined closely it will be seen that they have taken
up definite positions, forming lines and curves extending between
the two poles (Fig. 1). This is the simplest method by which the
magnetism may be made visible, and it illustrates the fact that the
power of a magnet acts in a series of lines passing from one pole to
the other. If a piece of iron or steel is placed across the poles of
a magnet these lines, or as many of them as possible, will use it as
a bridge or conductor, because they can pass through it more easily
than through air. Such a piece of iron or steel is called a keeper,
and by its use the magnet will retain its strength for a much
greater time than if the lines are obliged to make their way through
the far greater resistance that the air presents to their passage.

These lines, which are known as =magnetic lines of force=, always
move in the same direction, passing through the air or the keeper
from the north pole of the magnet to the south pole, and passing
through the metal of the magnet itself from the south pole to the
north pole.

The strength of a magnet depends on the number of these lines of
magnetic force that it possesses. If two magnets, one strong and the
other weak, are placed under sheets of paper on which iron filings
are scattered, their comparative strengths are clearly shown by the
difference in the number of lines of force that the filings show them
to possess.

The space through which a magnet makes itself felt is known as the
=magnetic field=, and this is large or small, according to the number
of lines of force. The stronger the magnet, the larger will be the
sweep of the curves of its lines of force, and the greater will be
the field that they form.

When a piece of iron or steel is placed in contact with a magnet, the
lines of force flow into it, and it becomes magnetized, throwing out
lines of force and forming its own magnetic field, which is quite
distinct from the magnetic field of the original magnet. If the piece
is of iron, its lines of force and its field die away as soon as it
is separated from the magnet, but a piece of steel once magnetized
will retain its magnetism and, of course, its lines of force.

A wire of nonmagnetic metal, such as copper, for instance, will not
have the slightest attraction for iron filings, but when an electric
current is passed through it the filings will act as if the copper
were a magnet, clinging to it as long as the current passes, and
dropping as soon as the circuit is broken. As a matter of fact, an
electric current sets up lines of magnetic force exactly similar to
those of a permanent magnet, their number being in proportion to the
strength of the current.

As has been stated, iron becomes magnetized when magnetic lines of
force flow into it. If, therefore, a wire through which an electric
current passes is wound around an iron rod, the lines of force set up
by the current will pass into the rod and magnetize it, so that it
sets up its own magnetic field. This magnetic field is created when
the electric current starts flowing in the wire and dies out when
the flow of the current is stopped, for then the lines of force due
to the current die out, and the iron, which depends on them for its
magnetism and which has not the ability to retain its lines of force,
returns to its original nonmagnetic condition. An arrangement of this
sort, consisting of a soft iron core, around which is wound a number
of layers of insulated wire, forms an =electro-magnet=, and will
produce a magnetic field whenever an electric current passes through
the wire. The action is practically instantaneous, the magnetic field
appearing and dying out on the making and breaking of the electric
circuit.

A magnetic field may thus be produced by the action of an electric
current, and an electric current in turn may be produced by the
action of a magnetic field. To generate a current by this method it
is only necessary to place a conductor forming a closed circuit in a
magnetic field, and to change the strength of the field, making it
stronger or weaker. For an example, a length of insulated wire may be
wound on an iron bar, and the bar then touched with a magnet. As soon
as the lines of force flow into the bar it becomes magnetized and
sets up a magnetic field in which the lines of force follow the law
and flow from one pole to the other through the air. The formation of
this field is exceedingly rapid, but during the time that the field
is forming and increasing to its full strength, an electric current
will flow in the wire winding. When the field has reached its full
strength, the flow of the current ceases. On separating the bar from
the magnet it loses its magnetism, and the field set up by it dies
away; or in other words, its strength undergoes another change, now
growing weaker as the bar returns to a nonmagnetic condition. This
dying out of the field generates another momentary flow of current in
the wire, which moves in the direction opposite to the flow of the
current generated while the strength of the field was increasing.

The current generated is called an =induced current=, and the method
of producing it is called =induction=.

The intensity of the induced current in any given winding depends
on the extent of the change in the strength of the field and upon
the rapidity with which it occurs. A bar of iron is limited as to
the strength to which it can be magnetized; or in other words, it
can only set up a limited number of lines of force. Increasing the
strength of the field from nothing to this point, or reducing its
strength from this point to nothing, gives the greatest change in
strength possible to obtain, and if this change occurs in the
shortest possible time, then the current induced will be of the
greatest intensity that can be obtained from a conductor of the size
and length used.

For an understanding of the action of a magneto it is necessary to
bear in mind the following points:

First. That a magnetic field is composed of lines of magnetic force
that flow from one pole of the magnet to the other.

Second. That the lines of force will take the path that presents the
least resistance.

Third. That an electric current will be generated, or induced, in a
conductor placed in a magnetic field whenever the strength of the
field changes.

Fourth. That the current flows only while the change in strength
is taking place, ceasing to exist when the field becomes uniformly
strong or weak.

To make a practical application of the laws governing the production
of an induced current, a conductor forming a closed circuit is
placed in a magnetic field, and the strength of the field caused
to change, alternately becoming strong and weak. In magnetos, the
magnetic field is due to two or more powerful steel magnets, and
the conductor, a length of insulated copper wire, is wound on a
soft iron core and revolved between the poles of the magnets where
the field is strongest. The magnets are known as the =field= of the
magneto, and the wire on its core the =armature=. The shape of the
iron armature core is shown in Fig. 2, the winding being indicated
by heavy black lines. On the inside of the poles of the field are
=pole pieces=, which are blocks of soft iron hollowed out to receive
the armature. As the successful operation of the magneto requires
the lines of force to have as easy a path as possible, the air space
between the armature heads and pole pieces is very small, being in
the neighborhood of 1/100 of an inch.

[Illustration: FIG. 2.—ARMATURE.]

[Illustration: FIG. 3.]

When the armature is not in position, the lines of force will be
required to pass from one pole piece to the other through the air,
and as they will seek the path of lowest resistance, most of them
will pass between the lower points of the pole pieces, where the
air gap is short, and where the lines of force are present in the
greatest number (Fig. 3). When the armature is placed between the
pole pieces, however, it gives the lines of force a path of still
lower resistance, and they will therefore follow it, whatever its
position may be. If the armature is free to turn, it will take a
horizontal position, as shown in Fig. 4, for then the heads are
entirely in contact with the pole pieces, and the greatest possible
number of lines of force can take the path offered by the neck of the
armature.

[Illustration: FIG. 4.]

[Illustration: FIG. 5.]

When the armature is in this position, the neck is magnetized by the
flow of lines of force through it and sets up a powerful magnetic
field which is quite distinct from the field thrown out by the field
magnets. If the armature is revolved, it takes the lines of force, or
most of them, with it, and they continue to flow through the neck as
long as one head of the armature is in contact with the north pole
piece and the other head in contact with the south pole piece, for
even this long and distorted path, as shown in Fig. 5, is of less
resistance than the air gap. The lines of force, however, resist
this lengthening of their path, and tend to hold the armature with
the neck horizontal, when their passage is easiest. If the armature
is turned by hand, it will be noticed that it becomes harder to turn
as the neck approaches the vertical position, and if the magnets
are sufficiently powerful, a great effort will be necessary. Once
vertical, however, the armature hangs, and a still greater effort
is required to continue the revolution, for the lines of force have
found new paths of low resistance (Fig. 6). Each armature head now
forms a bridge between the pole pieces, and the lines of force
divide, some going through the upper head and some through the
lower. The lines entirely abandon the neck, and in consequence its
magnetic field dies out. When these paths are broken by continuing
the revolution of the armature, the lines of force again flow through
the neck, and its magnetic field is again established (Fig. 7). This
action occurs twice during each complete revolution of the armature,
and if the armature is revolved by hand, the two points when the neck
is horizontal and the movement easy will be very distinct from the
hard points when the neck is going over the vertical position.

[Illustration: FIG. 6.]

[Illustration: FIG. 7.]

In one revolution the neck is twice magnetized and demagnetized; or
in other words, the magnetic field set up by the neck as the lines
of force pass through it twice changes its strength, being strong
when the neck is horizontal and weak when it is vertical. The winding
on the armature is affected by this magnetic field, and electric
currents are induced in it by these changes in its strength.

The greatest change in the strength of the field occurs as the
armature moves into the vertical position, when its heads form
bridges between the two pole pieces (Fig. 6). Up to this point the
armature neck is strongly magnetized, but its magnetic field dies
out as the neck becomes vertical. It is at this point then that the
induced current is at its greatest intensity and becomes sufficient
for ignition purposes.

In making an armature the channels are wound full of wire, and this
is retained against the action of centrifugal force by two or three
short lengths of wire bound around the armature and lying in grooves
cut in the heads for that purpose. Disks of brass are also screwed
to the ends of the armature core, and assist in making it dust and
water proof. The magneto must have a base, and this must be of some
nonmagnetic metal, like brass, for if it were made of iron it would
provide a convenient path for the lines of force, and they would
have no interest in passing through the armature. There must also be
bearings for the armature shaft, and these are either plain or ball,
set in brass plates screwed to the ends of the pole pieces. A zinc
or aluminum plate covers the space over the armature and between the
upper edges of the pole pieces, so that the armature revolves in a
tunnel that is proof against the entrance of dust and water.

There are, of course, two ends to the wire wound on the armature,
but the simplicity of a magneto is increased by grounding one end
on the metal of the armature, the other end being brought to the
single terminal (Fig. 2). The circuit is therefore complete when this
terminal is connected to any metal part of the magneto; or, as the
magneto is mounted directly on the metal of the engine, to any metal
part of the engine or frame of the car. The live end of the armature
winding is brought out by means of a metal rod passing lengthways
through the shaft of the armature, the rod being insulated from the
shaft by means of a hard rubber bushing or tube. The terminal of the
winding is therefore found at one end of the armature shaft, and the
current flows from this revolving part to the stationary binding post
by means of a carbon or steel spring that is kept pressed against the
end of this rod.

Magnetos are classified as L. T. (low tension) and H. T. (high
tension) according to the current that they deliver, the word tension
being used to indicate the pressure or voltage of the current, but
more accurate expressions would be primary and secondary magnetos.
The magneto already described is of the low-tension type, and is
used for the make-and-break ignition system, its winding being so
proportioned that at maximum speed it delivers a current of from 100
to 150 volts. What is often spoken of as a high-tension magneto is
employed for the jump spark system, a magneto of the type described
delivering a current that flows through the primary winding of a
secondary induction coil; but this use of the term is erroneous, for
while the system delivers a high-tension spark, this is from the
coil. The magneto itself is not only of the low-tension type, but
its current must be so feeble that the danger of burning out the
coil is obviated. A true high-tension magneto has two windings on
the armature; one, the primary, consisting of a few layers of coarse
wire, over which the very great number of layers of fine wire forming
the secondary is wound. This may give a current of from 10,000 to
20,000 volts, and is used for the jump spark ignition system.

These types and their applications will be discussed in the
succeeding chapters.


                         MAGNETOS IN GENERAL

One of the great advantages resulting from the use of a magneto is
that for ordinary running it does away with the necessity for the
hand advance of the spark. The greater the speed at which a magneto
runs, the more abrupt is the change in the strength of the magnetic
field, and in consequence the greater is the intensity of the
current delivered. When running at slow speed, the spark produced in
the cylinder will be weak and thin; it will be sufficient to ignite
the mixture, but the ignition will occur slowly. At high speeds, on
the contrary, the intensity of the current produced will be such
that a flame rather than a spark will be produced, and ignition will
occur much more rapidly and positively. When starting an engine on
the magneto, the spark control lever must be advanced more than is
necessary for ignition by battery, and the engine must be cranked
at such a speed that the magneto will produce a current sufficient
for ignition. Once started, it is rarely necessary to move the spark
control lever, except for high speeds, for speeding the engine up by
opening the throttle will increase the speed of the magneto, and the
flaming spark will result in a quicker ignition of the mixture.

Because a magneto does not deliver a continuous current, it cannot
be driven by a belt or by friction, for a slight slip would throw it
out of time with the engine. The best drive is by gears, for this
is positive, and there is a minimum of lost motion. In some cases
the magneto is driven by chain and sprocket, and while this prevents
slipping, there is considerable lost motion when the chain is loose
enough to run smoothly, and the magneto cannot be timed as accurately
as is possible with gears.


                          MAGNETO TROUBLES

If the ignition fails, and the question arises as to the reason,
the condition of the magneto may be tested quickly and in a most
satisfactory manner. It either gives a current or it does not, and
to learn its condition it is only necessary to disconnect it from
the ignition system, and to connect one end of a length of wire to
its terminal. Holding the free end of this wire in the bare fingers
of one hand, and cranking the engine with the other hand, also bare,
a shock will be felt as the armature revolves, if it is in good
condition. If this test is too strenuous, the free end of the wire
may be held lightly against the teeth of a gear while an assistant
cranks the engine briskly. As the wire falls from tooth to tooth, a
time will come when the point of maximum current coincides with the
breaking of the circuit at the gear, and if the magneto is in good
condition, a flaming spark will appear.

There is little about a magneto of the type described to get out of
order. Oil or dirt between the spring or brush and the end of the
conducting rod may prevent the flow of current, or, what is more
unlikely, the wire of the armature may be broken. The last trouble
is of rare occurrence, for when winding the wire on the armature it
is shellacked, and for all practical purposes the whole becomes a
solid mass. The only point where the wire can break is the half-inch
of it that is connected to the inside end of the conducting rod that
passes through the shaft, and the condition of this may be learned
by removing the dust cover and looking. If broken, a drop of solder,
carefully applied, will repair the damage.

A question that is frequently asked is regarding the liability of
the field magnets to lose their magnetism. If made of the proper
material, and handled and used under proper conditions, they should
hold their magnetism indefinitely. The strength of a toy magnet may
be increased by tearing its keeper sharply away from the poles, and
as sharply replacing it, the operation being repeated. When the
armature of a magneto revolves, it performs the same office for the
field magnets, and it has the effect of keeping them up to strength
indefinitely. If the magneto is mishandled, however, it is another
story, and an inquisitive or careless worker can almost instantly
weaken a field by removing the armature without taking the proper
precautions. The armature, when in position, acts as a keeper, and
provides a path of low resistance for the passage of the lines of
magnetic force. If the keeper is taken away, the lines of force are
required to traverse the higher resistance of the air, and many
of them then being overcome, their number decreases and the field
becomes greatly weakened. This takes place instantly on the removal
of the armature. It is rarely necessary for a chauffeur to remove the
armature of a magneto, but when it is required, the first step is
the placing of a heavy plate of iron under the arch of the magnets,
and in close metallic contact with the pole pieces, the dust plate
being removed. This will act as a keeper, and the armature may then
be removed. If such a plate of iron is not at hand, both of the end
plates may be unscrewed and one of them removed, and then, as the
armature is drawn out slowly, small steel tools, or short lengths of
iron rod, well cleaned, may be fed in after it, so that the cavity
is well filled. If these precautions are taken the armature may
be removed with safety, but it is better not to attempt this, and
it is never advisable to detach the magnets from the base or pole
pieces. So much damage may be done to a magneto by an unskilled man,
that some of the manufacturers go to the length of equipping their
magnetos with seals, the breaking of which is evidence that the
machine has been tampered with, and that someone is directly to blame
if it does not deliver current.

When an engine is equipped with a double system of ignition, or
when there are two sources of current, one being a magneto, the
greatest care must be taken to prevent even the momentary flow of
the battery current through the armature winding, for this will
result in the demagnetization of the field. The same trouble will
result if the magneto current is led through the winding of a primary
induction coil in the hope of intensifying the current. Should the
battery current flow through the armature winding, the core would be
magnetized, for it would then be an electro-magnet, and the magnetic
field set up by the armature under such conditions would overcome the
less powerful field set up by the field magnets and their strength
would instantly be reduced.

It is very essential to keep the armature bearings thoroughly
lubricated in order that there may be as little wear as possible. The
clearance between the armature heads and the pole pieces is so slight
that a trifling amount of wear in the bearings would permit the two
to rub or strike. The best magnetos are equipped with ball bearings,
provided with wick feeds that keep them lubricated, but even with
these the lubrication must be watched. Oil cups are provided, which
must be kept filled, but it must be remembered that an excess of oil
may make trouble in working its way into the armature winding and
destroying the insulation. In some cases the oil cups are provided
with an overflow, which prevents excessive oiling and the collection
of surplus oil around the bearings.


                     LOW-TENSION IGNITION SYSTEM

In utilizing the current of a magneto for ignition purposes, the
circuit is so arranged that it is first closed and then opened,
the closing of the circuit permitting the current to flow, and the
breaking of the circuit resulting in a spark at the break. The
closing and opening of the circuit is due to the action of the
=igniter=, which is a device located in the cylinder wall, one end
projecting into the combustion space and the outside end bearing the
parts by which it is operated. The two chief parts of an igniter
are the =stationary= and =movable electrodes=, so arranged and
connected that when the movable electrode comes into contact with
the stationary electrode the circuit is closed, and when it moves out
of contact the circuit is broken.

The stationary electrode is a steel pin or screw passing through
the cylinder wall, and carefully insulated from it by a tube or
bushing of mica or other insulant that is proof against the heat and
pressure produced in the combustion space. The current developed
by the magneto is led to this stationary electrode. The movable
electrode rocks in a bearing in the cylinder wall, the inside end
of its short shaft carrying a finger that touches or separates from
the stationary electrode as the shaft is rocked. The outer end of
the short shaft carries one or two short arms by which the shaft is
moved. The operation of the igniter is due to the action of a cam on
the half-time shaft, which moves a =tappet rod= that in turn acts on
the arm controlling the movable electrode.

When the cam is not acting on the tappet, the movable electrode is
held out of contact with the stationary electrode, and there is
consequently no circuit for the current. As the tappet is moved by
the revolution of the cam, the movable electrode is freed and is
brought into contact with the stationary electrode by the action of
a light spring. This closes the circuit, and the current flows. The
further revolution of the cam separates the movable electrode from
the stationary, and the sudden breaking of the circuit results in the
production of a spark between the two.

There is a great variety in the construction of igniters, but the
operation is the same in all. Once in its revolution the cam operates
the movable arm of the igniter, permitting it to touch the stationary
electrode, and this establishment of the circuit is followed by
its rupture as the continued movement of the cam causes the tappet
again to operate the movable electrode. A better spark for ignition
purposes is obtained when the movable electrode is moved out of
contact with the stationary electrode sharply than when it is moved
slowly, and for this reason the parts are so arranged that the
tappet strikes the movable electrode a blow instead of pushing or
pressing it. This construction is shown in Fig. 8. When the cam is
not acting on the tappet, the head on the tappet holds the movable
electrode away from the stationary, against the action of a light
spring. As the cam lifts the tappet, the tappet head releases the
movable electrode, and the light spring draws it upward and against
the stationary electrode, establishing the circuit. When the tappet
drops off the cam, it is brought down sharply by the tappet spring,
and its head strikes the movable electrode a sharp blow that results
in the sudden breaking of the circuit.

[Illustration: FIG. 8.—MAKE-AND-BREAK SYSTEM.]

In some types, the movable electrode comes into contact with the end
of the stationary electrode, which is then a screw, and the distance
between them may be adjusted by screwing it in or out. In other
types, contact is made with the side of the stationary electrode,
in which case the adjustment of the distance is provided for on the
movable electrode. This distance should be about one sixteenth of an
inch, for this is ample for the production of a satisfactory spark,
and a greater distance will result in the more rapid burning of the
contact points.

In multicylinder engines, the current from the live end of the
armature winding is led to a =bus-bar= of conducting material that
serves to distribute it to the igniters. The stationary and insulated
electrode of each igniter is connected to this bus-bar by a short
length of wire that either leads through a switch of ordinary
construction, or is provided with a plug on its end that fits into
a socket on the bus-bar and serves the purpose of a switch by which
the igniters may be thrown out of circuit when it is desirable. As
the magneto is grounded when it is placed on the engine, and as the
movable electrode of the igniter is also grounded on the engine, a
circuit for the current is provided only when a movable electrode is
in contact with a stationary electrode. The construction of the cam
shaft is such that only one igniter at a time makes contact, which
occurs during the compression stroke, so that the rupturing of the
circuit will occur at the point in the compression stroke when the
spark is required for ignition.

To cut off the ignition circuit for the purpose of stopping the
engine, it would be bad practice to break the contact between the
magneto and the bus-bar, for while this would bring the desired
result it might result in the injury of the magneto, as there would
then be no circuit for the current that the magneto would still be
developing. The best practice is to short-circuit the magneto, and
this is provided for by means of a simple switch, one point of which
is grounded, and the other connected to any insulated part of the
ignition system; the magneto terminal, bus-bar, or other. When this
switch is closed, a circuit is provided for the magneto current,
which, in the arrangement shown in Fig. 8, flows from the magneto to
the bus-bar, to the switch (when closed), to ground, and back to the
magneto. If this circuit is provided, the current will follow it,
abandoning the paths across the igniters as they operate, and the
production of sparks ceasing, the engine will come to a stop.


                     SETTING UP THE L. T. SYSTEM

To obtain successful results, the spark must be produced at the
correct point in the compression stroke, and this requires such
adjustment of the igniters that the movable electrode breaks the
circuit at this point. Because the magneto delivers a fluctuating
current, it is clear that the most satisfactory spark will be
produced when it is so set that it will be delivering its maximum
current at the instant that the igniters separate. As most of the
running of a car is done on an advanced spark, the point of maximum
advance must be determined in order to set or adjust a low-tension
ignition system. This point varies with different engines; in a
large proportion the piston has a “lead” of one half inch, while in
a smaller number the “lead” varies from this to three quarters of
an inch. By this it is meant that when advanced, the spark occurs
when the piston still has one half inch to travel to reach top dead
center of the compression stroke, or anything up to three quarters of
an inch, as the case may be. Inquiry of the manufacturers regarding
this point will secure the information, but if this is not possible,
the point may be found by experiment.

The first step is to bring one of the pistons to within one half
inch of top dead center of the compression stroke. This position
may be determined by dropping a stiff wire through a compression
relief cock or other opening in the cylinder head, so that it rests
on the piston and is moved by it. The crank shaft of a four-cycle
engine must make two revolutions to complete the cycle in one of the
cylinders, and during these two revolutions the piston will twice
pass top dead center, as will be shown by the movements of the wire.
It is necessary, however, to distinguish between top dead center of
the compression stroke and top dead center of the exhaust stroke, and
this may be accomplished by watching the stem of the exhaust valve.
When the wire shows that the piston is moving toward top dead center,
and the exhaust valve stem shows the valve to be open, the piston
is known to be making the exhaust stroke, and to get it to top dead
center of the compression stroke it is necessary to continue the
revolution of the crank shaft while the piston moves downward on the
inlet stroke, and again upward on the compression stroke. During this
second upward stroke the exhaust valve stem will not move, showing
the valve to be closed. Cranking must stop when the lack of movement
of the wire shows the piston to be at top dead center, and then the
crank shaft must be turned backward by means of the flywheel until
the piston has moved down one half inch. This may be determined
by making a mark on the wire and holding a rule firmly in such a
position that as the wire follows the piston the mark will move along
the graduations. When the mark has moved down one half inch below top
dead center, the movement of the crank shaft must be stopped so that
the piston is held in that position.

Place the spark control lever in the advanced position, when the
nose of the cam should be just ceasing to act on the tappet. The
movable electrode must then be adjusted so that it is in the act of
separating from the stationary electrode, and this is performed by
shortening or lengthening the tappet, or otherwise setting the parts
so that the tappet head is in contact with the outside arm of the
movable electrode and beginning to move it away from the stationary
electrode. This point may be accurately determined by the use of
an electric bell circuit. Connect a bell with three or four dry
cells, grounding the free terminal of the battery on the engine. Then
breaking any connection between the igniter terminal and the ignition
system, connect the free terminal of the bell to the igniter. The
circuit will then consist of battery, bell, igniter, and ground
return, and the bell will ring when the movable electrode is making
contact with the stationary. Having adjusted the movable electrode so
that it is approximately correct, it may be tested by cranking the
engine. The bell should begin to ring during the compression stroke,
and should stop ringing when the marks of the wire show the piston to
be one half inch from top dead center. The igniter of each cylinder
must be adjusted separately, and when tests have shown them to be
correct, the lock nuts must be set up to hold them in position.

In attaching the magneto to the engine, means must be provided for
driving it at the proper speed. In a four-cylinder engine, two
revolutions of the crank shaft are necessary for the production of a
cycle in each of the cylinders, two power strokes occurring in each
revolution. As the magneto delivers its maximum current twice in each
revolution of the armature, it must be driven at the speed of the
crank shaft, and as the drive is usually taken from the cam shaft,
the gear on the magneto must have half as many teeth as the gear on
the half-time shaft with which it meshes. To set the magneto, the
crank shaft should be revolved until one of the pistons (it makes no
difference which) is in the firing position; that is, the position
for which the igniter is set to open. The armature should then be
revolved by hand until it is just past the vertical position of Fig.
6, with about one sixty-fourth of an inch of space showing between
its rear edge and the edge of the pole piece from which it is moving.
This can most easily be accomplished by removing the dust cover and
reaching under the arch of the field with the fingers. Holding the
armature in this position, its driving gear should be slipped into
mesh with the gear on the half-time shaft.

In some makes of magnetos the gear is keyed to the armature shaft,
which determines its position in relation to the armature. In this
case, the gears must be meshed as close to the indicated position
as possible. In other designs the magneto is driven by a positive
clutch, so that it is impossible to mesh it in any but the correct
position. In Bosch magnetos there is no key, but the shaft is
tapered to fit a tapered hole in the gear, so that a very exact
setting of the magneto is possible.

When the gear is keyed to the armature shaft, the closeness of the
setting depends on the thickness of the teeth; the thinner the teeth,
the closer it is possible to adjust the magneto. If the armature gear
has an uneven number of teeth, however, it is possible to make the
setting by one half the thickness of a tooth. If it is found that
the thickness of the teeth is such that the armature cannot be set
correctly, give the armature and its gear a half turn, when, if the
number of teeth is odd, it will be found that a tooth on one side
corresponds to the space between two teeth on the opposite side.

Having set the magneto and drawn up the nut securing the gear to the
armature shaft, the system may be wired by running a wire from the
terminal of the magneto to the bus-bar, and other wires from the
bus-bar to each of the igniter terminals. The short circuiting switch
should also be connected up, the running of its wires depending on
convenience.

The system installed, it should be tested. With the system adjusted
as indicated, the engine should start, and a very short run will show
if it is correct. If it does not respond to advancing the spark,
or if its operation is not satisfactory, a readjustment should be
made, giving the piston a lead of one eighth of an inch more, or five
eighths of an inch in all, with the spark advanced. If this shows an
improvement, but the engine still does not develop its full power,
the operation may be repeated, the piston being given more lead by
one sixteenth of an inch.

If the compression is not the same in all of the cylinders, a
closer adjustment of the igniters may be made that will improve the
operation of the engine, the tappet of the high compression cylinder
being adjusted to operate the movable electrode slightly before the
others, so that the larger volume of mixture will have more time in
which to burn. The switches through which the igniters are connected
to the bus-bar may now be brought into use, and when three of them
are open the engine should run on the single cylinder of which the
circuit is complete. Testing the cylinders in this way, running one
at a time, gives an opportunity for comparing their action, and for
noting those in which the power is weak. If the weakness is due to
ignition trouble, it may be corrected by a further adjustment of the
tappet.


                              TROUBLES

Failure of ignition due to magneto trouble has already been described.

Any short circuit of the system will prevent ignition, for the
current will not flow across the igniters if another path is open
to it. Short circuiting may be due to the chafing of the insulation
of the wires, to a frayed end of a stranded cable making contact
with the metal of the engine, to the carbonization or breaking of
the insulation around a stationary electrode, or to the sticking
of a movable electrode in contact with a stationary. Operating the
igniters by hand will show the presence of this last named condition,
and inspection of the insulation and terminals the presence of
any defects. Loss of power is frequently due to the leakage of
compression around the plate carrying the igniter, around the
stationary electrode, or through the bearing in which the movable
electrode rocks. The side of the bearing toward the combustion space
is built like a valve, and when worn may be ground to a seat.

If the engine runs well at low speed, but misses at high speed, the
fault may be located in faulty insulation of one of the stationary
electrodes, which holds the low-pressure current developed by
the magneto at low speed, but fails to retain the higher pressure
developed when the speed is increased. The faulty igniter may be
located by running the engine one cylinder at a time.

The heat developed by the spark is very great, and provisions must
be made to preserve the contact points from undue corrosion. These
points are usually made of platinum, or of an alloy of platinum and
iridium, and must be kept clean and smooth. The spring that draws the
movable electrode against the stationary must not be too strong or it
will bring the contacts together with sufficient force to batter them
out of shape. This spring should be of sufficient strength to bring
them together promptly, but without undue force. The tappet spring
should be of considerable strength, in order that the separation of
the electrodes may be quick and positive.

After long running the contacts will become worn to such an extent
that the spark occurs too late in the stroke to permit the engine
to develop its full power. This may be corrected by readjustment of
the tappets, so that ignition takes place earlier. A wearing of the
outside arm of the movable electrode, or of the tappet head, will
have the same effect.

Another cause of failure will be the weakness of the spring of the
movable electrode, which is so weakened that it will not do its work
at high speed.


                  L. T. MAGNETO WITH SECONDARY COIL

The advantages of a magneto as a current producer for the low-tension
system pointed the way to its adoption for the jump spark system
also, but it was at once recognized that it would be impossible to
lead the current direct to the primary winding, as the current from
a battery is used. The reason for this is that while the battery
delivers a current of constant value, the current obtained from a
magneto is fluctuating, its intensity depending on the positions of
the armature as it revolves, and the speed at which it is driven.
A current is induced in the secondary winding of the coil as the
magnetic field set up by the core changes its strength, and as has
been explained, the induced current is strongest when the greatest
change in the strength of the field occurs in the shortest possible
time. The effect of the flow of the magneto current through the
primary winding of the coil would be to magnetize and demagnetize the
core slowly, as the magneto current increased to its maximum and
died away to the minimum, and these gradual changes in the magnetic
field of the core would induce currents in the secondary that would
be too feeble to produce ignition of the charge. When a battery
is used with a coil, the operation of the vibrator produces rapid
magnetizations and demagnetizations of the core, but as the field
set up by the core dies away more rapidly than it is established,
the greatest current is induced by the breaking of the circuit. In
the best known method of applying a magneto to the operation of a
secondary coil, the magnetization of the core is caused to occur with
exceeding rapidity, and the current induced in the secondary winding
as this occurs is sufficient for ignition.

This is known as the Eisemann system, and is in very general use. A
diagram illustrating the connections is shown in Fig. 9.

[Illustration: FIG. 9.—EISEMANN IGNITION SYSTEM.]

The magneto is of the usual type, but the winding is so proportioned
that the current is of lower voltage than is delivered by what has
been described as the low-tension type of magneto. One end of the
winding is grounded on the metal of the armature, and the live end
is carried to a contact screw. The current flows to this screw, and
from there two paths are presented by which it may flow back and
complete its circuit. One of these paths leads through the primary
winding of a secondary coil, and the other through a lever that
for the greater part of the revolution of the armature touches the
contact screw. The lever is grounded on the metal of the magneto, and
when it touches the contact the circuit that is then completed is
short and of low resistance, and the current follows it in preference
to the circuit of higher resistance through the primary winding of
the coil. The flow of current is thus from the armature winding to
the contact screw, which is insulated from the metal of the magneto,
to the lever, and by the ground back to the winding. Attached to the
end of the armature shaft, and so placed that it operates the lever,
is a cam with two projections, these projections being arranged to
move the lever away from the contact screw. This arrangement is
called the =interruptor=, and by its operation it closes and opens
the low-resistance circuit by which the magneto current may flow.

When the armature is horizontal, and during the time that it
is approaching the vertical, the circuit is closed through the
interruptor, but when the armature reaches the position in which it
gives its maximum current, the interrupted is opened by the cam, and
the current, losing its low-resistance circuit, is required to flow
through the primary winding of the coil, for that is the only path by
which it can return to the armature winding. The sudden flow of this
current through the primary winding results in the production of a
powerful magnetic field around the core, and this rapid growth in the
strength of its field induces a current in the secondary winding that
is sufficient for the ignition of the charge. As the magneto current
is at its maximum twice during each revolution of the armature, the
cam is arranged to open the low-resistance circuit at such periods
that each maximum is required to flow through the primary of the coil.

In applying this system to a multicylinder engine, it is necessary
to distribute the secondary current to the different cylinders, so
that a spark will be produced in each as it is required. This is
accomplished by means of a =secondary distributor=, consisting of
a revolving conductor to which the secondary current is led, and a
stationary contact for each cylinder arranged in a circle, to be
touched as it revolves. These stationary contacts are connected
with the spark plugs, according to the firing order of the engine.
During one revolution of the distributor, a spark is produced in
each of the cylinders, and as two revolutions of the crank shaft
are necessary in order to have power strokes occur in all of the
cylinders, the distributor must revolve at half the speed of the
crank shaft. The magneto produces a current that is sufficient for
ignition twice during each revolution of the armature, and therefore,
for four cylinder engines, must run at the speed of the crank shaft.
For the sake of compactness, the distributor is built into the
magneto, its shaft being carried in bearings that support it above
the armature and under the arch of the field magnets. It is geared
to the armature so that the two revolve in a fixed relation to each
other, and in order that the distributor may run at half the speed of
the armature, its gear has twice the number of teeth of the gear on
the armature shaft that drives it.

The secondary induction coil used is similar in construction to the
coils used for ignition by battery, except that it is heavier, and
has no vibrator. The period during which the magneto is delivering
its maximum current is so brief that there would hardly be time for a
vibrator to get into action, and even if this were not the case, the
making and breaking of the circuit by the vibrator is not necessary,
as the single change in the strength of the magnetic field set up by
the core is so abrupt that the current induced by it is sufficient
for the purpose.

The strength of this secondary current is such that it is necessary
to provide a circuit for it if by any accident or oversight the
circuit through the distributor or spark plugs is interrupted,
as would be the case should one of the secondary wires become
disconnected. This is taken care of by what is known as the =safety
spark gap=, which is a gap provided between the secondary terminals
of the coil, or between the live end of the secondary winding and
the ground. This safety spark gap, in the case of the coil furnished
by the Eisemann company, takes the form of two flat pieces of brass,
each in contact with one of the secondary terminals of the coil,
their pointed ends being separated by a distance of about half an
inch. When there is no interruption of the secondary circuit, and
the parts of the secondary system do not present undue resistance
to the flow of the current, the higher resistance of the air space
between the points of the safety spark gap prevents the current from
jumping between them, but should one of the secondary cables become
disconnected, the pressure of the current will rise to a point that
will enable it to jump the gap between the two points. If it were
not for this safety gap, an interruption of the secondary circuit
would make the pressure of the current rise to such an extent that
there would be great danger of a spark passing inside of the coil,
rupturing the insulation.

As the magneto is received from the makers, the parts will be in a
fixed relation to each other; when the armature is vertical, and
held in that position by the lines of force, the cam is in the
act of opening the primary interruptor, and the revolving part of
the secondary distributor has moved into contact with one of the
stationary contacts about one thirty-second of an inch.

The interruptor of the magneto can be utilized as the timer for
an ignition system by battery and coil, the secondary current
being distributed to the cylinders by the distributor. A better
arrangement, however, requires the use of two coils, and a timer
which is carried on the rear end of the distributor shaft. The coil
for the battery system is provided with a vibrator, and connections
are made in the manner usual with a system composed of these parts.
The coil is in a case that also contains the non-vibrator coil for
the magneto system, and the two wirings are separate and distinct
with the exception of the secondary connection between the coil box
and the revolving parts of the distributor, which is common to both.

While little change in the position of the spark is required for
this system, provisions are made by which it may be advanced or
retarded. In one system, the interruptor is operated by a groove in
the face of the cam disk, a pin on the end of the interruptor lever
following the groove and being moved by the irregularities. In this
case, the advance and retard of the spark is obtained by rotating
a plate carrying the interruptor in one direction or the other, so
that the lever is moved earlier or later in the revolution of the
cam. In another type the gear driving the armature is not attached
direct to the armature shaft, but to a sleeve surrounding the shaft,
and the pulling out of a second sleeve between the two alters the
position of the armature in relation to the driving gear, resulting
in the advancing or delaying of the moment when the maximum current
is produced.


                        SETTING UP THE SYSTEM

In setting up a system of this description, the firing order of
the engine must be ascertained, and this may be done by watching
the order in which the exhaust valve stems move as the engine is
slowly cranked. Piston No. 1 must then be brought to top dead center
of the compression stroke, and about one thirty-second of an inch
down on the power stroke, being stopped in this position. With
the magneto screwed into place, the covers of the interruptor and
distributor may be removed, and the armature revolved by hand in the
direction in which it will be driven, until the interruptor opens,
the spark control being in the most retarded position. A mark on the
interruptor will come into line with a mark on the casing at the
instant that the interruptor breaks contact. The magneto gear should
then be meshed with the gear that drives it, and the lock nut set up.

The connection between the live end of the armature winding and the
interruptor is arranged by the maker, but it is necessary to make
connections between the magneto and the coil. A terminal will be
found in the casing close to the stationary contact screw, and this
is to be connected with one of the primary terminals of the coil,
the other primary terminal either being grounded on the engine or
the magneto, according to the construction. The moving part of the
secondary distributor may then be connected with the secondary
terminal of the coil. If the coil has but three terminals, two
primary and one secondary, there are no further coil connections to
be made, but if, as is sometimes the case, there are two secondary
terminals, the free one is to be grounded on the engine.

An inspection of the distributor will show that the revolving part is
beginning to make contact with one of the stationary points, and this
point is to be connected to the spark plug of the cylinder in which
the piston is at top dead center of the compression stroke. The next
distributor point in the direction of rotation is to be connected
with the spark plug of the next cylinder to fire, the remaining
distributor points and spark plugs being connected in the order of
firing.

Magnetos of this type are built to run in either clockwise or counter
clockwise, and the two are not interchangeable. The direction in
which the magneto is to be driven is indicated by an arrow stamped on
the gear casing or end plate.

When the system is properly installed, the motor should start on a
quarter-turn of the crank shaft, the crank being given a quick upward
jerk. If it does not, the setting is incorrect, the connections are
improperly made, or there is too great a distance between the points
of the spark plugs. This distance should be one sixty-fourth of an
inch.


                                CARE

The bearings of the armature and secondary shafts must be kept well
lubricated, as well as the parts of the interruptor that require it.

Every few weeks, depending on the use, the carbon or steel brush
bearing against the live end of the armature shaft must be wiped off
with gasoline, and the same care must be given to the distributor
contacts and to the platinum contacts of the interruptor.

When the platinum contacts of the interruptor become worn down after
long use, or if for any other reason they require readjustment, they
must be set so that the distance between them at the moment that the
cam holds them apart is not more than one one-hundredth of an inch.
This space may appear to be very small for the work that is to be
performed, but it will be sufficient, and a greater distance will
result in sparking that will burn down the contacts. In the Eisemann
magneto, the adjustable contact is held by two nuts, and small open
end wrenches are provided to fit. A wrench should be applied to each
of these nuts, and the lower or lock nut loosened. This will free the
upper nut by which the adjustment may be made, and the lock nut may
then be tightened. The contact faces of the platinums should be kept
flat and smooth, and true to each other, so that they come together
squarely. If they are pitted after long use they may be faced off
with a dead smooth file, but this is a job that requires great care,
and must only be done under the most favorable conditions. When
completely worn down they should be replaced with new ones.


                              TROUBLES

Should the engine show a tendency to miss, the first suspicion, if
the magneto contacts are known to be correct, should fall on the
spark plugs, and the easiest method of testing them out is to replace
them with new ones. After considerable use, the spark plug points
will burn off, and the size of the gap will increase to such an
extent that the spark will find less resistance in traversing the
safety spark gap than the gap in the plug.

In order that the ignition may be cut off for the purpose of stopping
the engine, a switch is always provided by which the magneto may
be short circuited, one pole of the switch being connected to the
magneto terminal, or live wire, and the other pole grounded, as shown
in Fig. 9. When this switch is closed, the magneto current flows
through it in a closed circuit, and as it abandons its path through
the interruptor there will be no further action in the coil, the
ignition of course ceasing. This switch is often located in the rim
or arm of the steering wheel, so arranged that pressing on a button
closes the circuit and diverts the magneto current from the coil.

Any accidental short circuit of the magneto current will produce the
same effect, and in case of the abrupt cessation of ignition, this
is one of the probable causes. A short circuit in the secondary will
usually make itself known by the snapping of the sparks as they pass
through broken insulation or from a frayed cable end.

The remarks on general magneto troubles and care already made on
page 254 also apply to a magneto of this type, and the same rules
regarding the protecting of the circuit of the lines of the field
must be borne in mind.


                        H.-T. MAGNETO SYSTEMS

A high-tension magneto differs from the types described in that the
armature has a double winding; one, the primary winding, consisting
of a few layers of coarse wire, and the secondary winding, placed
over the primary, consisting of many layers of very fine wire. As
the armature revolves, a current is induced in the primary winding,
the circuit of which is kept closed until the armature reaches the
position in which the induced current is at its greatest value. An
interruptor operated by a cam then opens the primary circuit, and
the sudden demagnetization of the armature core that results induces
in the secondary winding a current of high pressure that is quite
sufficient to jump the gap in the spark plug and to cause ignition of
the mixture. The construction of the armature is more delicate than
is the case with a low-tension magneto, for the secondary winding
must have a large number of layers, and to permit this in the limited
space, the wire must be fine. In addition, it must be insulated with
the greatest care, for the intensity of the current produced will
enable it to seek out and to break down any weakness that exists.
There must also be two brushes, one for the primary current and one
for the secondary, which complicates the construction.

[Illustration: FIG. 10.—WIRING DIAGRAM, H.-T. MAGNETO INTERCHANGEABLE
WITH SECONDARY COIL.]

A magneto of this type is shown in diagram in Fig. 10. In this
case, the inner ends of both the primary and secondary windings
are grounded, the live end of the primary being connected with the
insulated contact of the interruptor, and the live end of the
secondary leading to the rotating part of a secondary distributor.
For the greater part of the revolution of the armature, the cam on
the armature shaft permits the interruptor to maintain a closed
circuit, but as the current reaches a maximum the cam breaks the
circuit, and the flow of the primary current ceases. During this
time, the secondary circuit has been open, the moving part of the
distributor being out of contact with the stationary points. Under
the law of induction, a current will only be induced in a closed
circuit, and there is therefore no action in the secondary winding.
When the primary current is at its maximum and its circuit is broken,
another condition exists, for then the secondary distributor is
making contact, the only gap being in the spark plug, but the sudden
demagnetization of the armature core as the primary circuit is
broken, and the additional effect as the armature passes the vertical
position, induces in the secondary winding a current of great
intensity that passes to the spark plug by way of the distributor,
returning to the winding by the ground.

The parts of the interruptor are carried on one of the end plates of
the magneto, and the secondary distributor revolves in bearings that
support it under the arch of the magnets.

In the diagram shown provisions are made for a double ignition
system, the operator having his choice of ignition by high-tension
magneto direct or by battery, timer and coil. In practice, the three
switches shown operate together. When magneto ignition is desired,
the switch between the battery and ground is opened, and the switch
at the secondary distributor thrown into contact with the point
connected with the secondary terminal of the magneto. The third
switch is thrown to make contact between the primary terminal of the
magneto and the interruptor. If battery ignition is desired, the
switch on the magneto primary is thrown to the point through which it
is grounded, and the primary and secondary switches of the battery
circuit closed. The upper contact points of the interruptor are then
utilized to close primary circuit of battery, and the secondary
current induced in coil is led to distributor. This complication of
switches is necessary to prevent possibility of the battery current
flowing through the armature winding, and to provide a short circuit
for the primary of the magneto. If the engine is running on magneto
ignition, it is stopped by throwing the primary switch to the point
by which the primary is grounded. If running on battery, the circuit
is broken in the usual way.

The current from a high-tension magneto is of such intensity that
the small points of an ordinary spark plug would quickly be burned,
and it is necessary to provide plugs with heavy points, which will
stand the work. The distance between the points should be about one
sixty-fourth of an inch.

The Bosch magnetos, which are perhaps in more general use than any
other, are built on similar lines to the magneto just described,
except that the grounded end of the secondary winding, instead of
being attached to the metal of the armature, is connected to the live
end of the primary winding, as shown in Fig. 11. The live end of the
primary is brought out through a conducting rod passing lengthways
through one end of the armature shaft, from which the current flows
to the stationary contact of the interruptor. While in other magnetos
the interruptor parts are stationary and operated by a moving cam,
in this type the interruptor parts revolve with the armature, and
the moving arm is operated by two fiber wheels as it drags around
the inside of a stationary ring. By rotating the ring and the two
wheels the interruptor is caused to operate sooner or later in its
revolution, this giving the advance and retard of the spark.

[Illustration: FIG. 11.—WIRING DIAGRAM, TWO-SPARK MAGNETO.]

The other end of the armature shaft carries the collecting ring
for the secondary current, this consisting of a hard rubber disk
around the surface of which is a metal ring to which the live end of
the secondary winding is connected. A carbon brush is kept pressed
against this metal ring by a light spring, and the current is thus
led off to the revolving part of a secondary distributor.

The interruptor keeps the primary circuit closed until the current
induced in the primary winding is at its maximum, when the opening
of this circuit causes the rapid demagnetization of the core, and
a powerful current is induced in the secondary, which flows to the
spark plug with which the distributor is making contact.

A safety spark gap is applied between the brass strip that conducts
the secondary current from the collecting brush to the distributor,
and the metal of the magneto. The necessity for this device has
already been explained, and it is essential that a magneto of this
type should be so provided, because of the intensity of the current.


                               SETTING

[Illustration: FIG. 12.—TIMING DIAGRAM, TWO-SPARK MAGNETO.]

In setting up a system of ignition with a magneto of this type,
the firing order of the engine must be observed, and then one of
the pistons brought to the point in the compression stroke that it
will occupy when the spark is at the greatest advance. As has been
explained in the case of engines equipped for the make and break
system, this point will usually be from one-half to three-quarters
of an inch before top dead center, the greater proportion of designs
placing it at one-half an inch. The driving gear of a Bosch magneto
is not keyed to the armature shaft, but shaft and gear are tapered,
so that when the nut is drawn up tight there is no possibility of
slipping. After the magneto is secured in position its gear may be
meshed with the gear that is to drive it, but without drawing up
the nut. The armature may then be turned by hand until it is in the
vertical position, where it will be retained by the lines of force
(Fig. 12), and the gear nut drawn up tight. If this position of the
armature cannot be obtained by the sense of touch, it may be exposed
to sight by the removal of the bridge that carries the safety spark
gap, and of the dust cover that protects the space between the upper
sides of the pole pieces.

The loosening of the three-armed frame on the front of the magneto
will permit the removal of the covers of the interruptor and timer,
and it will be seen that the moving part of the distributor is
beginning to make contact with one of the stationary pieces; this
should be connected to the spark plug of the cylinder that is in the
firing position. The other contacts of the distributor should then be
connected to the remaining spark plugs in the order of firing.

Ignition is cut out by short-circuiting the primary winding, and a
binding post will be found on the front of the magneto under the
three-pronged frame to which is connected the wire that leads to a
switch making a ground connection when closed.


                                CARE

The armature and distributor shafts run on ball bearings, and
these require the application of a few drops of oil twice a month.
The interruptor is designed to operate without oil, and there is
therefore little danger of oil working its way into the winding.

The carbon brushes must be wiped off with a little gasoline
occasionally, and these are arranged in such a manner that they are
easy of access.

The platinum contacts of the interruptor must be kept free from dirt
and oil, and when, after long use, they become worn and uneven, they
must be faced off by the use of a dead smooth file. The distance
between them when separated by the action of the fiber rollers
must not be more than one sixty-fourth of an inch, and this may be
adjusted by means of the nuts. Accompanying each magneto is a small
open end wrench for this purpose, to which is pivoted a leaf of steel
that is to be used as a gauge for this distance.

This same measurement applies to the spark plugs, the points of which
must provide a gap of not more than one sixty-fourth of an inch.


                              TROUBLES

If there is an abrupt failure of ignition, it is probable that the
primary is short-circuited, and this can only occur on the wire that
leads to the short-circuiting switch, for the other parts of the
primary circuit are inclosed and protected against injury.

In case of the missing of one cylinder only, the trouble will usually
be found in the plug, which may be short-circuited by a carbon
deposit, or because the intense heat of the spark has fused the
metal, resulting in the formation of a globule of metal between the
spark points. Too great a distance between the points, more than one
sixty-fourth of an inch, will prevent the passing of the spark, which
will then be seen in the safety spark gap.

A miss in different cylinders may be due to defective insulation of
the wires, but if these are in good condition the fault may be looked
for in the magneto. The place where trouble is usually experienced
is in the interruptor, which may become dirty, or the contacts may
be worn down or loosened from the vibration. Fouled contacts in the
distributor may also lead to a miss-fire, and this will be corrected
by wiping the parts with gasoline. If all of these parts have been
examined and found correct, it is inadvisable to examine further into
the magneto, for inexperienced handling will be likely to injure the
delicate parts. It is better to place it in the hands of a man whose
shop is equipped for the work.


                         FOUR-SPARK MAGNETO

All of the magnetos described have been of the type in which the
armature revolves, and two ignitions are secured per revolution.
These are known as two-spark magnetos, or crank-shaft speed magnetos,
from the fact that for four cylinder engines the magneto runs at
the speed of the crank shaft. This is in distinction to the Bosch
four-spark, or cam-shaft speed, magnetos, in which the armature as
well as the field is stationary. This magneto for its simplicity,
freedom from trouble, and workmanship, has few equals for the
high-tension ignition of an internal combustion engine.

The armature in this magneto is of the usual type, and is stationary,
with the armature neck in a vertical position. Around the armature,
and between it and the pole pieces, revolves a soft iron shield
in two sections, these being the length of the armature and the
same width as the heads. As it revolves, it forms bridges between
the pole pieces and the core of the armature, the lines of force
flowing through it as well as through the armature. The diagrams of
Fig. 13 show the positions of the shield as it revolves about the
armature. In the first position, one segment of the shield forms a
bridge between the pole piece and the upper armature head, while
the other segment is bridging the space between the lower head and
the other pole piece. When in this position, the lines of force
flow through the neck of the armature and magnetize it so that it
sets up its own field. When the shield revolves so that it covers
the heads, the lines of force abandon the neck and flow between the
pole pieces by the segments, the field established by the neck dying
out. In the third position, the lines of force again flow through
the neck, while in the fourth position, with the shield completing
a half revolution, the lines of force again pass directly across.
In this half revolution there are therefore two periods when a
magnetic field forms around the armature neck and dies out, which
will result in the induction of two currents in the winding of the
armature. If the revolution is continued it will be seen that the
same conditions are repeated, the positions of the two segments of
the shield being reversed, and that one revolution of the shield
about the armature will produce four waves of current in the winding.
The magneto may therefore be driven at cam shaft speed for a four
cylinder engine, and in addition has the advantage of the wire
windings being stationary. The action of the magneto is the same as
that of the two-spark type already described, but the construction
is simplified because the slow speed of the shield will permit the
secondary distributor to be attached directly to the armature shaft,
the secondary shaft being done away with.

[Illustration: FIG. 13.—DIAGRAMS SHOWING POSITION OF SHIELD REVOLVING
ABOUT ARMATURE.]

A diagram of the wiring is shown in Fig. 14. The primary wiring is
grounded, and the live end brought out to the stationary contact
point of the interruptor. The moving part of the interruptor is
pivoted in the center, and the lower end, a polished steel knob,
bears against the face of a disk that has four ribs running from
center to edge. When the knob is on the space between two of the
ribs, the interruptor closes the circuit, but as the disk revolves
and a rib touches the knob, the arm moves on its pivot, and the
circuit is broken.

[Illustration: FIG. 14.—WIRING DIAGRAM, FOUR-SPARK MAGNETO.]

The grounded end of the secondary winding is attached to the live end
of the primary winding, and its other terminal passes to a contact
point carried on a hard rubber disk placed on the revolving shaft
immediately in front of the interruptor. The diagram shows a face
view of this distributor, as well as a side view. A ring-shaped plate
is set on one side of this disk, and is in connection with a contact
piece carried on the edge of the disk. A carbon brush to which the
live end of the secondary winding is attached is kept pressed against
the ring-shaped plate, and the secondary current is thus led to the
contact piece on the edge of the disk. As the disk revolves with the
shaft of the shield the contact piece comes into successive contact
with four carbon brushes, which are connected to the spark plugs.

When the shield is in such a position that the lines of force flow
through the neck of the armature, the interruptor is closed, but
when the intensity of the current increases to the maximum the
interruptor opens, breaking the primary circuit, and producing a
rapid demagnetization of the armature core. This dying out of the
field induces a powerful current in the secondary winding, which is
led by the distributor to one of the spark plugs, where it jumps the
gap and returns to the winding by the ground connection.


                               SETTING

In setting the magneto the firing order of the engine is noted, as
has been explained, and the magneto secured in position with its gear
in mesh, but loose on the shaft. The cover over the space between the
pole pieces will be found to be in the form of a shallow aluminum
box, which is held in position by a single screw with a large head,
and when this is removed the stationary armature and revolving shield
will be exposed to view. One of the pistons must then be brought
into the position it will take with a fully advanced spark, and
the shield then revolved until it is in the position shown in Fig.
15. The nut securing the gear to the shaft may then be drawn up
tight. It will be noticed that one of the segments of the shield has
a deep notch at each edge. Remembering the direction in which the
shield will be driven, the notch at the rear edge of the shield will
indicate the position of the contact piece of the distributor which
will then be coming into contact with the carbon brush of one of the
stationary distributor contacts. The spark plug of the cylinder that
is in the firing position should be connected to the brush that the
notch indicates as making contact, and the remaining spark plugs and
brushes connected according to the firing order.

[Illustration: FIG. 15.—TIMING DIAGRAM, FOUR-SPARK MAGNETO.]

                                CARE

The proper operation of the magneto requires the free and perfect
action of the interruptor, and this may be observed by means of a
brass slide that operates on the arm or the spark control lever.
When this slide is raised, the action of the interruptor may be
watched. Like the two-spark Bosch magneto, the distance between
these points when the disk separates them should be one sixty-fourth
of an inch, and contact should be made and broken without undue
sparking. The condenser that will be found in the shallow aluminum
box covering the space between the pole pieces prevents sparking at
the interrupter, and is thrown into circuit automatically when it is
placed in position.

The four-spark magneto is provided with a safety spark gap, and when
the points of one of the spark plugs are separated too far, or when
there is any interruption of the secondary circuit, a spark will
show there. Sparks should not be permitted to pass in the safety
gap for any considerable period, as damage will be done, and when
they indicate by their presence that something is wrong, the trouble
should be located and repaired without delay.

The regulation and care of the four-spark magneto is the same as has
been described for the two-spark machine.


                        DUAL IGNITION SYSTEMS

It has been the custom to equip jump-spark engines with two complete
systems of ignition, one operated by a magneto and the other by coil
and battery. Each system has its own spark plugs, timing device,
wiring, etc., the two being connected only at the switch. Many of
these duplicate parts have been eliminated by the introduction
of =dual ignition= systems, and the mechanism is correspondingly
simplified. The Bosch dual system is a good example of the
principles involved, and a diagram of the connections is shown on
Fig. 16. The magneto used is of the usual two-spark type, except
that the secondary current, instead of being led from the collecting
ring direct to the distributer, is taken to the switch that is
located in the coil box on the dash. In addition to the regulation
interrupter illustrated on Fig. 11, the magneto is provided with a
second interrupter or circuit breaker that controls the flow of the
battery current, and takes the place of a timer. While the magneto
interrupter revolves with the armature, and is operated by stationary
cams, the battery circuit breaker is stationary, and is operated by
a two-nose cam that revolves with the armature shaft. The stationary
and revolving cams are so set that the interrupter and circuit
breaker break their circuits at the same instant.

The coil is contained in a brass case on the dash, and in design and
construction is a duplicate of the magneto armature. Attached to
the coil is a handle that projects through a slot in the case, by
means of which the coil may be turned partly around in the case. The
terminals of the coil windings are attached to metal knobs located
on the under side of a fiber plate that forms the bottom of the
coil, and turning the coil by the handle moves these knobs in and
out of contact with corresponding knobs on the bottom of the case.
These knobs form the switch that cuts off all current, or permits the
engine to be run on magneto or battery. When the switch is in such a
position that the magneto produces secondary current, this flows from
terminal 3 of the magneto to terminal 3 of the switch; thence by the
switch connection to terminal 4 and to the secondary distributer.
When the battery is switched in, the magneto primary is grounded, and
secondary current from the coil flows over wire 4 to the secondary
distributer.

[Illustration: FIG. 16.—BOSCH JUMP-SPARK DUAL SYSTEM.]

By pressing a button on top of the coil case, a vibrator is cut into
the circuit to permit starting the engine on the spark. When the
engine starts the button is released, and ignition is produced by the
single spark that results from the demagnetizing of the core that
follows the breaking of the battery circuit by the circuit breaker.
Throwing the switch breaks the battery circuit and cuts in the
magneto.


                          INDUCTOR MAGNETOS

In types of magnetos that have recently been produced, the winding
is stationary and surrounds a moving core that is magnetized and
demagnetized during its revolution between the poles of the field
magnets. The Remy magneto is of this type, and Fig. 17 is a diagram
of the revolving core, or inductor, with the coil surrounding it. As
the inductor revolves, the magnetism flows from one pole of the field
magnets into the wing of the inductor nearest to it, through the
central cylindrical part, and by the second wing to the other pole,
the central part of the inductor then being magnetized. The magnetism
of this portion dies away when the wings are in such a position that
they bridge across from one pole to the other, but reappears when the
central cylindrical part again becomes the only path by which the
magnetism may flow. The constant changes in the magnetic strength of
the central part affect the coil, and currents are induced in it.
These currents, which are of low voltage, are led to the primary
winding of a secondary induction coil similar to that used in the
Eisemann system, the secondary current flowing to the plugs through
a distributer located on the magneto. In the Remy system, the
interrupter does not short circuit the magneto winding, as is the
case with the Eisemann, but the flow of current is from the magneto
winding to the grounded side of the interrupter, to the insulated
screw, to the primary winding of the coil, and back to the magneto.
The interrupter is closed and the current flows in this circuit while
the strength of the current is increasing, but when the current is at
a maximum the interrupter breaks the circuit, the core of the coil
loses its magnetism, and a secondary current is induced. The current
reaches a maximum twice in each revolution.

[Illustration: FIG. 17.—REMY INDUCTOR.]

[Illustration: FIG. 18.—INDUCTOR GIVING SIX WAVES.]

In other magnetos, the form of the inductor is such that six or more
waves of current are produced during each revolution. An inductor of
this type is shown in Fig. 18. There are six arms radiating from the
central cylindrical portion, three at each end, and equally spaced.
The coil is usually made of flat copper ribbon instead of wire, and
it surrounds the central cylindrical part between the two sets of
arms. In the inductor shown, the magnetism of the central part will
change strength six times to each revolution.

Magnetos of this type are used to replace batteries in jump spark
systems using vibrator coils. They are driven by belt, or by friction
against the fly wheel, and are given a speed at least three times
that of the crank shaft. By this means the waves of current follow
one another at such brief intervals that the flow is practically
continuous, and it is therefore unnecessary to time the magneto
to the engine. These magnetos have no interrupters, and the wiring
consists of one wire leading to the switch on the coil box, the usual
connections between the coil box and timer, and a wire from the
second magneto terminal to ground.


                   MAGNETIC MAKE-AND-BREAK SYSTEM

The flaming spark produced by the make-and-break system has many
advantages for ignition over the jump spark produced by the
high-tension system, but these are largely offset by the mechanical
complication of cams, tappets, springs, etc. A make-and-break system
in which the igniters are operated by magnetism has been perfected by
the Bosch company, and is giving good results. The magneto used is of
the ordinary low-tension type, equipped with an interrupter, while
all of the igniter parts are contained in a plug that screws into the
cylinder wall like a jump-spark plug. The plug is shown in diagram
in Fig. 19. The sleeve that screws into the cylinder supports an
iron core, the two being thoroughly insulated by blocks and washers
of heat-proof insulating material. The upper portion of the core
has a flat side, on which is formed a projection that serves as a
pivot. A hammer bar is balanced on this pivot, its long end passing
through the plug and coming into contact with an anvil attached to
the screwed sleeve. A long horseshoe-shaped spring holds the two in
light contact, and the hammer bar then forms the only path by which
an electric current may pass from the core to the screwed sleeve and
to the engine ground. When the hammer bar is moved on its pivot this
connection is broken. Surrounding the core is a coil consisting of a
few layers of wire covered with heat-proof insulation. The upper part
of the plug is incased in a light iron casing screwed to the core,
which completely incloses the core, hammer bar, spring and coil,
and in which there is no opening that would permit the escape of
compression from the combustion chamber. One terminal of the coil is
connected to the binding post, and the other is grounded on the iron
casing. The current generated in the magneto passes to a distributer
and thence to the binding post of the plug, as shown in Fig. 20. It
flows through the coil to the core, and thence by the hammer bar to
the engine ground and back to the magneto. As the current establishes
itself in the coil, the core becomes magnetized, and attracts to it
the flat end of the hammer bar. When the hammer bar moves on its
pivot, its connection with the anvil is broken, and this break in
the circuit produces a flaming spark that is in every way identical
with the spark of the ordinary mechanical make-and-break igniter. The
casing that contains the coil may be unscrewed from the core without
disturbing the screwed sleeve, and this makes it an easy matter to
give the moving parts the inspection and cleaning that they should
receive every few weeks. The spark occurs in the plug at the instant
that the interrupter operates, and the setting up of the system is
identical with that of the high-tension magneto systems.

[Illustration: FIG. 19.—MAGNETIC IGNITER.]

[Illustration: FIG. 20.—WIRING DIAGRAM OF MAGNETIC IGNITER SYSTEM.]

                        A HANDY TESTING CHART*

                    WHAT TO DO WHEN THE ENGINE STOPS

                  Arranged for the Scientific American

                    (Copyright, 1909, by Munn & Co.)

                           EFFECTS OF TROUBLE

  =Engine=          { Test Ignition and
  =will=            {   carbureter.
  =not=             { Slow cranking or cold weather will interfere with
  =start.=          {   the proper formation or the mixture.
                    { Prime cylinders with gasoline in cold weather
                    {   to obtain mixture for starting.
                    { To increase suction in carbureter, prevent
                    {   operation of air-valve.

  =Engine starts,=  {
  =but will not=    { Fuel does not flow freely to carbureter.
  =continue=        { Weak battery.
  =running.=        {

  =Explosions=      { Break in ground wire, battery
  =cease=           {   connections, switch lead.
  =abruptly.=       {

  =Engine runs=     { Worn timer.
  =well slowly,=    { Weak battery.
  =but misses=      { Faulty vibrator adjustment.
  =when speeded=    { Faulty carbureter adjustment.
  =up.=             { Fuel does not flow freely to carbureter.

  =Engine will=     { Preignition.
  =not stop.=         { Glowing carbon or metal point in cylinder.
                    { Engine too hot (see Cooling trouble).

  =Engine does=     { Faulty setting of valves.
  =not deliver=     { Tight bearings or broken balls.
  =full power.=       { Indicated by excessive heating.
                    { Back pressure.
                       { Fouled muffler.
                    { Dragging brakes.
                    { Friction in transmission.
                    { Faulty carburetion.
                    { Weak ignition.
                    { Weak compression.
                    { Overheating.

                    { Slipping timer.
                    { Loose half-time shaft.
                    { Sticking air-valve.
  =Irregular=       { Intermittent obstruction in spray nozzle.
  =miss.=           { Sticking valve.
                    { Broken or weak valve-spring.
                    { Loose connection.
                    { Short circuit.

  =Engine noises.=  { Knocking.
                       { Too much retard of spark.
                       { Preignition.
                       { Worn bearings.
                       { Loose or cracked flywheel.
                    { Hissing.
                       { Broken piston rings.
                       { Leaking air inlet pipe or gasket.
                    { “Popping” in carbureter.
                       { Leaking inlet valve.
                       { Weak mixture.
                       { Excessive retard of spark.

  =Explosions=      {
  =weaken and=      { Carbureter or fuel trouble.
  =cease.=          {

  =Engine will=     { Weak magneto.
  =not run=         { Faulty carbureter adjustment.
  =slowly.=         {

  =Steady miss=     {
  =in one or more=  {
  =cylinders,=      { Vibrator, timer, secondary circuit.
  =(other=          {
  =cylinders=       {
  =firing=          {
  =normally).=      {

  =IGNITION.=       { Test primary circuit
  =Jump spark,=     {   as described for
  =with single=     {   system using coils
  =coil, battery=   {   and timer.
  =secondary=       { Secondary may
  =distributor.=    {   short circuit from
                      { Fouled or worn distributor.
                      { Defective insulation.

  =IGNITION.=       { To test, revolve crank-shaft
  =Jump spark,=     {   twice, listening
  =with battery,=   {   for vibrators.
  =timer and=       {
  =coils.=          { =TEST 1. Alternate test,=
                    {   =prime cylinders with=
                    {   =a few drops of gasoline,=
                    {   =close relief cocks,=
                    {   =and crank.=
                    { =Explosions show ignition=
                    {   =to be O. K.=
                       { All vibrators sound normal, primary circuits
                       {   O. K. unless timer has slipped on shaft.
                         { Vibrator should begin to operate as a piston
                         { gets to top center of compression, with
                         { spark lever retarded.
                       { One or more vibrators   }
                       {   sound normal,         } To test coils, short
                       {   showing that          }   circuit the timer
                       {   battery connections,  }   by making contact
                       {   lead and              }   between primary
                       {   ground wires, and     }   terminal of
                       {   battery are O. K.     }   coil and ground.
                         { Vibrator normal,
                         { coil is O. K.,
                         { look for
                           { Interruption in timer circuit.
                         { Blade moves, but
                         {   will not vibrate.
                           { Punctured condenser ([1]).
                           { Short circuit at vibrator.
                         { Vibrator does not
                         {    operate.
                           { Faulty adjustment.
                             { Too stiff.
                               { Will operate only with strong battery.
                               { Excessive sparking at vibrator, and
                               { battery exhausts rapidly.
                             { Too weak.
                               { Feeble secondary spark; misfiring with
                               {   slightly corroded contacts.
                           { Contacts corroded.
                           { Contacts stuck.
                       { Vibrators do not operate.
                         { Open switch; vibrator trouble.
                         { Trouble in battery or in primary circuit.
                           { To test, make momentary contact from switch
                           { terminal to ground.
                              { Bright spark, battery lead
                              {   and ground wire O. K.
                              { Weak or no spark.
                                { Break in battery connections,
                                {   lead or ground wire.
                                { Battery exhausted or dry cells
                                {   polarized.
                    { To test secondary, disconnect spark
                    {   plug leads, support them ⅜ inch from
                    {   engine ground and crank.
                      { Good spark, O. K.
                      { Weak spark.
                      { No spark.
                        { Vibrator trouble.
                        { Plug short circuited, fouled, oily.
                        { Points too far apart—should be 1/32 inch.
                        { Short circuit in secondary.
                        { Broken condenser connection ([1]).
                          {Shown by brilliant sparking at vibrator.

                    { Explosions.
                      { Ignition O.K. unless
  =IGNITION.=           { Magneto is out of  time and igniters
                        {   incorrectly adjusted.
  Make and break,         } Should break circuit at top center
  with low                }   of compression when spark is retarded.
  tension magneto.  { No explosions.
                      { Short circuit.
  Use Test 1,           { Insulated bridge on magneto.
  cranking              { Switch or switch lead.
  briskly.              { Bus-bar or bus-bar lead.
                        { Igniter insulator broken.
                        { Igniter stuck closed.
                        { Broken spring.
                        { Tappet stuck in guide.
                           { To test operate by hand.
                    { Open circuit.
                    { Magneto broken down.
                      { To test magneto, disconnect magneto lead from
                      {   bus-bar and hold free end in bare fingers, or
                      { =TEST 2. Hold free end against teeth=
                      {    =of metal gear and crank briskly.=
                        { Shock or spark.
                          { Magneto O. K.
                        { No shock or spark.
                          { Fouled collecting brush.
                          { Armature burned out [1].
                             { Fields demagnetized [1].
                                { To test, unmesh gear, revolve armature
                                {   by hand. If fields are O. K.,
                                {   armature should turn perceptibly
                                {   hard twice in each revolution.

  =CARBURETER.=     {Mixture ignites.
                      { Proving that carbureter is doing its duty.
  To test, hold     { Mixture does not ignite. Operate primer to flood
  lighted match     {   float chamber.
  over open relief    { Gasoline drips from spray nozzle.
  cocks while           { Mixture too rich.
  engine is               { Insufficient air.
  cranked briskly.          { Faulty adjustment of air valve.
                            { Clogged inlet pipe.
                            { Dust on inlet pipe screen.
                          { Leaking float valve.
                          { Float too heavy.
                            { Soggy (if of cork) ([2]).
                            { Punctured (if of metal) ([3]).
                          { Faulty adjustment of float.
                        { Mixture too poor.
                          { Too much air.
                          { Water in gasoline.
                            { Faulty adjustment of air-valve.
                            { Leaks in inlet pipe.
                            { Faulty adjustment of float.
                      { No drip from spray nozzle.
                        { Clogged spray nozzle.
                        { Clogged float valve.
                        { Clogged fuel feed.
                        { No gasoline.
                        { Empty tank.
                        { Closed supply cock.

  =IGNITION.=       { Proceed as in Test 1, cranking briskly.
                      { Explosions.
  Jump spark with       { Ignition O. K. unless magneto is out of time.
  low tension           {   Should be reset.
  magneto and coil    { Sparks in safety spark gap.
  (Eisemann, Remy,      { Interruption in secondary circuit.
  Splitdorf, etc.)      { Too wide a gap at plugs (should be from 1/64
                        {   to 1/32 inch).
                      { No explosions.
                        { Primary circuit open.
                        { Primary short circuit.
                        { Magneto broken down.
                          { To test magneto, disconnect primary lead
                          {   to coil and proceed as in test 2.
                            { Shock (or spark), magneto O. K.
                            { No shock (or spark).
                              { Interrupter short circuited, wet
                              {   or oily.
                              { Field demagnetized ([1]).
                              { Condenser broken down (shown by
                              {   brilliant spark at interrupter) ([1]).
                        { Coil broken down.
                          { To test primary winding of coil disconnect
                          {   ground wire and proceed as in
                          {   second part of test 2.
                            { Spark, winding O. K.
                            { No spark.
                              { Winding broken ([1]) down or short
                              {   or open circuited.
                          { To test secondary winding of coil,
                          {   disconnect spark plug leads from magneto
                          {   and crank briskly, watching for sparks
                          {   at safety spark gap.
                            { Sparks, look for
                              { Plugs short circuited.
                                { Fouled.
                                { Insulation broken down.
                                { Fused metal bead at points.
                              { Secondary short circuit ([1]).
                                { Leads short circuited.
                              { Ground circuit open.
                            { No sparks, winding broken down.

  =IGNITION.=       { Proceed as in Test 1, cranking briskly.
                      { Explosions.
  High tension          { Ignition O. K. unless magneto is out of time.
  magneto (Bosch,       {   Should be reset.
  U. & H. Lacoste,    { Sparks in safety spark gap.
  Witherbee, etc.)      { Break in secondary circuit.
                        { Too wide a gap at plugs (should be from
                        {   1/64 to 1/32 inch).
                      { No explosions.
                        { To test magneto, disconnect spark plug leads
                        {   from distributor and crank briskly,
                        {   watching for sparks at safety spark gap.
                          { Sparks.
                            { Magneto O. K.
                            { Look for short circuits in
                              { Spark plugs.
                                { Fouled.
                                { Insulation broken down.
                                { Bead of fused metal between points.
                              { Switch lead.
                              { Switch.
                          { No sparks.
                            { Corroded interrupter contacts.
                            { Interrupter stuck.
                            { Armature burned out ([1]).
                            { Condenser broken down ([1]).
                            { Field demagnetized ([1]).


  =FUEL FEED=       { To test, open drain cock at carbureter.
  =SYSTEM.=           { Gasoline flows.
                         { System is O. K.
                      { Gasoline does not flow.
                         { Gravity feed.
                           { Clogged vent hole in filling cap.
                           { Clogged piping ([4]).
                         { Pressure feed.
                           { Sufficient pressure in tank.
                             { Clogged piping ([4]).
                           { Insufficient pressure in tank.
                             { Leaking tank or piping.
                             { Leaking filling cap.
                             { Stuck relief valve.

                    { To test, crank engine slowly, noting resistance,
                    {   which should be the same in all cylinders.
  =COMPRESSION.=    {   (Do not confuse constant mechanical
                    {   resistance with intermittent resistance of
                    {   compression).
                    { Inject oil into faulty cylinder.
                      { Improved compression indicates
                        { Stuck piston rings.
                          { Douse cylinder with kerosene and alcohol
                          {    ½ and ½ to cut carbon.
                        { Worn or scored piston rings.
                        { Scored cylinder walls.
                      { No improvement in compression indicates
                        { Worn or pitted valves.
                      { Leaking spark plug, igniter plate,
                      {   relief cock, etc.
                        { Test by running oil around these
                        {   and cranking.
                          { Leak indicated by bubbles.
                      { Piston ring splits in line.
                      { Broken piston rings.
                        { Crank case will be abnormally warm.
                      { Cracked walls or head.
                        { Indicated by water in cylinder.
                      { Sticking valves.
                      { Insufficient space between valve stem and
                      {    push rod.

                    { Radiator should heat evenly shortly
  =COOLING.=        {   after engine is started.
                      { Radiator does not heat.
  (Water.)              { Clogged circulation system.
                          { Empty tank.
                          { Clogged piping.
                          { Defective pump.
                        { Test by opening pet cocks.
                      { Radiator steams.
                        { Failure of lubrication.
                          { Indicated by groans from cylinders affected.
                            { Supply should be just sufficient to
                            {   produce faint whiff of blue smoke
                            {   at exhaust.
                        { Defect in circulation.
                        { Too much running on retarded spark or on
                        {   low speed.
                        { Slipping fan drive.

* It is taken for granted that the engine is capable of running
properly, that the tanks are filled, and that the switch is correctly
thrown.

[1] Return to makers for repair.

[2] Dry in oven, and coat with shellac.

[3] Plunge in hot water to expel gasoline and to locate leak. Repair
with solder.

[4] May be cleared with blast from foot pump.




                                INDEX


  Adjusting screw for vibrator, 103.

  Advance of ignition, 13.

  Advancing ignition by moving timer, 101.
    too far, 13.

  Air cooling, 34.
    requisites for, 35.

  Air inlet, auxiliary, adjustment of, 231.

  Air intake trouble, 197.

  Amperes, 77.

  Antifreezing mixture, 200.

  Antiskid devices, use of, 174.

  Armature of generator, 88, 256.

  Assembling springs, 229.

  Automatic carburetor, 58.

  Automatic valve, 25.
    action of, 26.
    adjustment of, 233.
    spring of, 27.

  Auxiliary air, necessity for, 56.

  Auxiliary air inlet, action of, 57.
    adjustment of, 231.

  Axle, dead rear, 152.
    live rear, 146.
    necessity for fixed front, 162.
    rear, floating, 148.
    sprung, effect of, 148.


  Back pressure, 18.

  Backfiring, causes of, 218.

  Balance of engines, 37.

  Band brake, 167.

  Battery, causes of trouble in, 182.
    cross-connected, 182.
    nearly exhausted, 183.
    recuperation of, 183.
    weak, effect of, 213.

  Battery connections, 84.

  Bearings, tight, effect of, 210.
    tight, testing for, 221.

  Bevel gears, necessity for, 142.

  Bosch magnetos, 301, 308, 317, 323.

  Brake, motor as, 170.

  Brake equalizer, 172.

  Brakes, 167.
    emergency and running, 169.
    tight, effect of, 210.
    testing for, 221.

  Broken wire, 181.

  Bus bar, 204.


  Cam, 26.
    action of, 26.
    parts of, 26.
    worn, effect of, 235.

  Cam shaft, 28.

  Carbon deposit from burned oil, 31.

  Carburetion, 52.

  Carburetor, action of, 55.
    adjustment of, 231.
    automatic, 58.
    cleaning of, 196.
    dirt and water in, 195.
    effect of varying speed on, 56.
    float feed, 53.
    flooding of, 195.
    mechanically controlled, 58.
    necessity for, 53.
    necessity for auxiliary air in, 56.
    parts of, 53.
    principle of, 53.
    surface, 64.
    testing of, 207.
    trouble in, causes of, 195.
    types of, 58.
    with central mixing chamber, 61.
    with side mixing chamber, 60.

  Carburetor adjustments, 58.

  Chains, care of, 225.
    cleaning and lubricating of, 225.
    driving, adjusting of, 225.

  Change speed mechanism, friction type of, 141.
    individual clutch type of, 138.
    necessity for, 119.
    planetary type of, 132.
    sliding gear type of, 120.

  Changing gear, principle of, 125.

  Charging of storage battery, 82.

  Check and relief valves, 72.

  Chemical generators, 80.

  Circuit breaker, magneto, 286.

  Circuit, jump spark system, 108.
    primary, testing of, 206.
    primary and secondary, 109.
    parts of, 97.
    secondary, testing of, 212.

  Circulation, failures of, 199.

  Circulation connections, troubles of, 199.

  Circulation of water, forced and gravity, 32.

  Classes of gasoline engines, 5.

  Cleaning, use of kerosene for, 224.

  Cleaning carburetor, 196.
    chains, 225.
    combustion space, 223.
    crank case, 224.
    differential, 224.
    gear case, 224.
    lubricator pipes, 202.
    spark plug, 187.
    tires, 222.

  Clearance, 17.

  Closing of exhaust valve, 17.
    of inlet valve, 8.

  Clutch, action of, 113.
    friction cone, 113.
    internal expanding, 118.

  multiple disk, 114.
    parts of, 116.
    necessity for, 112.
    reversed friction cone, 114.
    slipping of, effect of, 210.
    withdrawing of, when changing gear, 113.

  Coil trouble, causes of, 186.

  Coils, matching of, to cylinders, 230.
    testing of, 206.

  Cold, effect of, on starting engine, 209.

  Combustion, pressure from, 4.

  Combustion and explosion, 4.

  Combustion space, 8.
    carbonized, effect of, 215.
    cleaning of, 223.

  Commutator, 97.

  Compensating gear (see Differential).

  Compression, during exhaust stroke, 16.
    effect of, 10.
    on spark, 188.
    necessity for, 10.

  Compression leaks, 197.
    testing for, 211.

  Compression limit, 14.

  Compression trouble, causes of, 197.

  Compression-combustion stroke, 8.

  Condenser, action of, 109.

  Conductors and insulators, 76.

  Cone clutch, friction, 113.

  Connecting rod, 23.

  Connections, battery, 84.
    loose, effect of, 212, 213.
    making, 180.
    of secondary distributer, 111.

  Construction of bevel gear differential, 153.
    of primary induction coil, 93.
    of secondary induction coil, 96.
    of spark plug, 107.
    of spur gear differential, 157.
    of switch, 89.

  Contracting brake, 167.

  Control of steering, 164.

  Coolers, 32.

  Cooling, air, 34.
    requisites for, 35.
    failure in, effect of, 215.
    water, 31.

  Cooling cylinder, necessity for, 30.

  Cooling system freezing, 200.

  Cooling systems, 31.

  Cooling trouble, causes of, 199.

  Cooling water, flow of, 31.

  Corrosion, effect of, 181.

  Crank case, cleaning of, 224.
    depth of oil in, 224.

  Crank pin, 23.

  Crank shaft, 20.
    four-cylinder engine, 43.
    180°-, effect of, 39.
    360°-, effect of, 41.

  Crank shaft points, 22.

  Crank shaft throws, 38.

  Cranks, relative positions of, 22.

  Current, flow of, 75.
    induced, 94.
    secondary, 97.

  Cycle, 4.
    events of, 6.
    strokes of, 6.

  Cylinder, 25.
    faulty, testing for, 212.
    matching coils, to, 230.
    necessity for cooling, 30.

  Cylinder head, 5.


  Defects of surface carburetors, 64.

  Deposit from burned oil, 31.

  Differential, bevel gear, construction of, 153.
    cleaning of, 224.
    location of, 158.
    necessity for, 152.
    operation of, 165.
    spur gear, construction of, 157.

  Direct drive, 124.

  Disk, valve, 25.

  Disk clutch, 114.

  Distance rods, necessity for, 176.

  Distributer, causes of trouble in, 192.
    secondary, 110.

  Double-acting brake, 167.

  Double-chain drive, 150.

  Double-opposed engine, 38.

  Drag link, 162.
    bent, effect of, 228.

  Drive, double chain, 150.
    driving shaft, 144.
    final, 142.
    propeller or driving shaft, 144.
    single chain, 142.

  Drives, advantages of different types of, 158.

  Driving chains, adjusting of, 225.

  Driving gear ratios, 159.

  Dry cells, 80.
    voltage of, 81.

  Dynamo, action of, 88.


  Eisemann system, 283 _et seq._

  Electric current, generation of, by magnetism, 87, 254.
    production of, 80.

  Electrical measurements, 77.

  Electrolyte, 82.

  Electro-magnet, 87, 253.

  Emergency brake, 169.

  Engine, care of, 223.
    distinction between two-cycle and four-cycle, 5.
    effect of cold on starting, 209.
    failure of, to deliver full power, 209.
    to start, 208.
    four-cycle, 5.
    missing of, at high speed, 213.
    parts of, 20.
    starting, then stopping of, 214.
    stopping of, 216.
    timing of, 232.
    two-cycle, 47.
    two-cycle, action of, 49.
    vibration of, 37.

  Engine as a brake, 170.

  Engine balance, 37.
    four-cylinder, 41, 43.
    H. D. O., 38.
    three- and
    six-cylinder, 44.
    two-cylinder, 38.

  Engine types, advantages and disadvantages of, 45.

  Epicyclic gears (see Planetary).

  Equalizer, brake, 172.

  Events of cycle, 6.

  Exhaust stroke, 16.
    compression during, 16.

  Exhaust valve, closing of, 17.
    opening of, 15.

  Expanding brake, 167.

  Expanding clutch, 118.

  Explosion and combustion, 4.

  Explosions, missing, 211.
    weak, 210.


  Field, magnetic, 88, 251.
    of generator, 88.

  Final drive, 142.

  Firing order, 44.

  Float, punctured, 196.

  Float and float chamber, carburetor, 53.

  Float feed carburetor, 53.

  Floating rear axle, 148.

  Flow of cooling water, 31.
    of current, 75.
    of electricity, definition of, 79.

  Fly wheel, necessity for, 8.
    vibration absorbed by, 37.
    weight of, 42.

  Force circulation of water, 32.

  Fouled spark plug, causes of, 187.

  Four-cycle engine, 5.

  Four-cylinder engine balance, 43.

  Four-cylinder engine crank shaft, 43.

  Four-cylinder engines, 43.

  Freezing of water, 200.

  Friction transmission, 141.


  Gases, properties of, 1.

  Gasoline, dirt and water in, 193.
    separating water from, 193.
    spraying, necessity for, 57.

  Gasoline engine, action of, 4.
    classes of, 5.
    functions of (see Cycle).
    not self-starting, 18.
    power of, 18.
    without reserve power, 19.

  Gasoline feed pipe trouble, causes of, 195.

  Gasoline feeds, gravity and pressure, 66.

  Gasoline line, trap on, 73.

  Gasoline strainer, 73.

  Gasoline trouble, causes of, 193.

  Gasoline vapor, 52.

  Gear case, cleaning of, 224.

  Gears, two-to-one, 28.

  Generator field and armature, 88.

  Generator terminals or poles, 75.

  Generators of electric current, 81.

  Governor-controlled carburetor, 62.

  Gravity feed of gasoline, 66.

  Gravity system of water cooling, 34.

  Grinding valves, 226.

  Grounding the return, 79.
    the secondary circuit, 108.
    the timer, 101.

  Gudgeon pin (see Wrist Pin).


  Half time shaft, 28.

  Heat, 1.
    excessive, result of, 30.
    losses, 15.
    produced through resistance, 77.

  Horizontal double-opposed engine, 38.

  Hydrometer, 83.


  Igniter, 91, 268.
    adjustment of, 276.
    magnetic, 323.

  Igniter bearing, 190.

  Igniter contacts, 190.

  Igniter points, setting, 189, 276.

  Igniter tappet, 92.
    spring of, strength of, 190.

  Igniter trouble, causes of, 189.

  Ignition, affected by improper mixture, 12.
    affected by speed, 12.
    necessity for, 8.
    necessity for early, 11.
    speed controlled by, 14.
    too far advanced, 13.
    too far retarded, 13.

  Ignition advance, 13.

  Ignition lead (see Necessity for Early Ignition).

  Ignition retard, 13.

  Ignition system, parts of, 75.
    purpose of, 74.

  Ignition systems, 91.

  Ignition testing, 203.

  Ignition timing, 192.

  Ignition trouble, causes of, 179.

  Ignition wiring, 236.

  Imperfect combustion of mixture, 10.

  Improper mixture, ignition affected by, 12.

  Individual clutch, 138.

  Induced current, 94, 254.

  Induction and magnetism, 93, 254.

  Inductor magnetos, 319.

  Inflation of tires, 173.

  Inlet pipe, 53.

  Inlet stroke, 8.

  Inlet valve, closing of, 8.

  Inspection of car, 220.

  Insulators, 76.

  Interrupter points, smoothing, 295.

  Irreversible steering mechanism, 165.


  Jack shaft, 152.

  Jackets, water, 31.

  Joints universal, necessity for, 144.

  Jump spark system, action of, 96.
    circuit of, 108.

  Jump spark trouble, location of, 205.

  Jump spark wiring, 238.


  Kerosene, use of, for cleaning, 224.

  Knocks, 217.


  Lead and return wires, 78.

  Leaks of compression, 197.

  Limit of compression, 14.

  Lines of force, magnetic, 87, 251.

  Live rear axle, 146.

  Losses of heat, 15.

  Low tension system, action of, 91, 270.

  Lubrication, 34, 35.
    of chains, 225.
    of springs, 229.

  Lubrication systems, 36.

  Lubrication table, 244.

  Lubrication troubles, 201.

  Lubricator failure, effect of, 215.

  Lubricator pipes, cleaning of, 202.


  Magnetic field, 88, 251.

  Magnetic lines of force, 87.

  Magnetic make-and-break system, 323.

  Magnetic vibrator, 103.

  Magnetism, 86, 245.
    electric current generated by, 87.
    test for, 265.

  Magnetism and induction, 93, 254.

  Magneto, action of, 88, 95.
    classification, 261.
    drives, 263.
    dual systems, 300, 316.
    effect of changing speed, 262.
    Eisemann, care of, 294.
    high tension, four spark, 308.
    interrupter, 286.
    low tension, ignition by, 258.
    wiring of, 272.
    with secondary coil, 283.
    parts, 256.
    preserving magnetism of, 266.
    principles, 255 _et seq._
    removing armature of, 183, 266.
    Remy, 320.
    retention of magnetism of, 184, 266.
    safety spark gap, 289.
    starting engine with, 263.
    testing, 264.

  Magneto setting, 185, 274, 306.

  Magneto troubles, causes of, 183, 264.

  Magnetos, Bosch, 301, 308, 317, 323.
    high tension, care of, 305.
    principles of, 297.
    setting, 303.
    high tension, troubles of, 306.
    inductor type, 319.
    magnetic make-and-break, 323.

  Magnets, permanent and electro-, 87, 249, 253.

  Maintenance and construction, 220.

  Make-and-break ignition, action of, 91, 270.

  Make-and-break trouble, location of, 206.

  Make-and-break wiring, 240.

  Measurements, electrical, 77.

  Mechanical generator, action of, 86.
    care of, 88, 89.

  Mechanical vibrator, 103.

  Mechanically-controlled carburetor, 58.
    construction of, 62.

  Mechanically operated valve, action of, 26.

  Mixing chamber, carburetor, 53.
    central, 60.
    side, 60.

  Mixture, imperfect combustion of, 10.

  Muffler, necessity for, 30.

  Muffler explosions, causes of, 219.

  Multiple connection of battery, 85.

  Multiple disk clutch, 114.
    parts of, 116.


  Necessity for auxiliary air in carburetor, 56.
    for bevel gears, 142.
    for carburetor, 53.
    for change-speed mechanism, 119.
    for clutch, 112.
    for compression, 10.
    for cooling cylinder, 30.
    for differential, 152.
    for distance or radius rods, 176.
    for early ignition, 11.
    for fixed-front axle, 162.
    for fly wheel, 8.
    for ignition, 8.
    for muffler, 30.
    for spraying the gasoline, 57.
    for switch, 89.
    for timer, 98.
    for torsion rod, 148.
    for universal joints, 144.
    for valves, 8.
    for vibrator, 102.
    for withdrawing clutch when changing gear, 130.

  Negative pole, 76.

  Noises, 217.

  Nonconductors, 76.


  Ohms, 78.

  Oil, burned, deposit from, 31.
    depth of, in crank case, 224.

  Opening of exhaust valve, 15.

  Operation of differential, 155.

  Overheating, 215.

  Overheating, causes of, 199.
    warning of, 216.


  Parallel connection of battery, 85.

  Parts of engine, 20.
    of cam, 26.
    of carburetor, 53.
    of ignition system, 75.
    of magneto, 256.
    of multiple disk clutch, 116.
    of primary circuit, 97.
    of secondary circuit, 97.

  Permanent magnet, 87.

  Piston, 23.
    stuck, 216.

  Piston pin (see Wrist Pin).

  Piston rings, 24.
    care of, 223.
    setting of, 198.
    trouble of, 198.

  Planetary gear action, 136.

  Planetary type of change-speed mechanism, 132.

  Points, crank shaft, 22.

  Poles, positive and negative, 76.

  Poles of generator, 75.

  Ports of two-cycle engine, 47.

  Positive pole, 76.

  Power of gasoline engine, 18.
    of steam engine, 18.

  Power stroke, 15.

  Preignition, causes of, 215.

  Pressure circulation of water, 32.

  Pressure feed of gasoline, 66.

  Pressure from combustion, 4.

  Primary circuit, 109.
    parts of, 97.
    testing of, 206.

  Primary generators, 80.

  Primary induction coil, use of, 93.

  Production of electric current, 80.

  Progressive type sliding gear, 121.

  Propeller-shaft drive, 144.

  Properties of gases, 1.

  Protection of tires, 222.

  Pumps, water, 32.

  Purpose of ignition system, 74.

  Push rod, 28.


  Radiators, 32.

  Radius rods, necessity for, 176.

  Ratios, driving gear, 159.

  Rear axle, dead, 152.

  Reason for skidding, 174.

  Recuperation of battery, 183.

  Relative positions of cranks, 22.

  Remy magneto, 320.

  Renewing vibrator contacts, 186.

  Replacing valve springs, 227.

  Requisites for air cooling, 35.

  Resistance, 76.
    heat produced by, 77.

  Retard of ignition, 13.
    too far, 13.

  Return, grounding the, 79.

  Return wire, 78.

  Reverse, action of, 125.

  Reversible steering mechanism, 164.

  Revolution and stroke, 5.

  Rings, piston, 24.

  Rod, radius, necessity for, 176.
    torsion, necessity for, 148.
    valve lifter, 28.

  Running brake, 169.

  Running gear, 161.


  Seat, valve, 25.

  Secondary cells, 80.

  Secondary circuit, 109.
    grounding of, 108.
    parts of, 97.
    testing of, 212.

  Secondary current, 97.

  Secondary distributer, 110, 287.
    causes of trouble in, 192.

  Secondary induction coil, use of, 96.

  Secondary shaft, 28.

  Selective type, advantages of, 129.
    of sliding gear, 126.

  Series connection of battery, 85.

  Setting igniter points, 189.

  Setting magneto, 185.

  Setting piston rings, 198.

  Shaft, cam, 28.
    jack, 152.

  Shock absorbers, 176.

  Short circuit, definition of, 79.
    causes of, 187.

  Side chain drive, 150.

  Silencer, 30.

  Single-acting brake, 167.

  Single chain drive, 142.

  Six-cylinder engine balance, 44.

  Skidding, reason for, 174.

  Sliding gear, action of, 120.
    progressive type of, 121.
    selective type of, 126.

  Spark, effect of compression on, 188.

  Spark gap, size of, 188.

  Spark plug, 106.
    cleaning of, 189.
    distance between points of, 188.
    fouled, effect of, 212.
    trouble in, causes of, 187.

  Sparking in timer, 108.

  Speed, control of, by ignition, 14.
    effect of varying, on carburetor, 56.
    excessive, results of, 19.
    ignition affected by, 12.

  Spray nozzle, carburetor, 55.

  Spraying gasoline, necessity for, 57.

  Springs, assembling, 229.
    automatic valve, 27.
    care of, 228.
    lubrication of, 229.
    vehicle, action of, 175.

  Steam engine, action of, 2.
    power of, 18.

  Steering, 161.
    control of, 164.
    principle of, 163.

  Steering arm, bent, effect of, 228.

  Steering knuckles, 162.

  Steering mechanism, care of, 227.
    irreversible, 165.
    reversible, 164.

  Stem, valve, 25.

  Storage battery, charging of, 82.

  Storage cell, action of, 81.
    terminals of, 83.
    voltage of, 84.

  Strainer, gasoline, 70.

  Stratified mixture (see Imperfect Combustion of Mixture).

  Stroke and revolution, 5.

  Strokes of cycles, 6.

  Sun and planet gears (see Planetary).

  Surface carburetors, 64.

  Switch, necessity for, 89.

  Switch trouble, causes of, 193.

  Systems, cooling, 31.


  Tank, air-bound, 194.

  Tank trouble, causes of, 194.

  Tappet, igniter, 92.
    spring of, 92.
    strength of, 190.

  Terminals of generator, 75.
    of storage cells, 83.

  Testing carburetor, 207.
    coils, 206.
    electrolyte, 83.
    for compression leaks, 211.
    for faulty cylinder, 212.
    for tight bearings and brakes, 221.
    ignition, 203.

  Testing, make-and-break, 204.
  primary circuit, 206.
  secondary circuit, 212, 213.

  Thermosiphon system of water cooling, 34.

  Three-cylinder engine balance, 44.

  Throttle, 62.
    worn connections of, effect of, 232.

  Throws, crank shaft, 38.

  Timer, 97.
    control rods of, effect of wear on, 191.
    grounding of, 101.
    loose on shaft, 191.
    moving of, to advance ignition, 101.
    necessity for, 98.
    setting of, 192.
    sparking in, 106.
    trouble of, causes of, 191.

  Timers, types of, 98.

  Timing magneto, 185.

  Tires, 172.
    cleaning of, 222.
    protection of, 222.
    reducing the
    cutting of, 223.
    unevenly worn, cause of, 228.

  Torsion rod, necessity for, 148.

  Transmission, parts of, 112.

  Trap on gasoline line, 73.

  Trembler (see Vibrator).

  Trouble, air intake, 197.
    battery, causes of, 182.
    carburetor,
    causes of, 195.
    circulation connections, 199.
    coil, causes of, 186.
    compression, causes of, 197.
    cooling, causes of, 199.
    engine failing to deliver full power, 209.
    engine failing to start, 208.
    engine missing at high speed, 213.
    engine starting, then stopping, 214.
    engine stopping, 216.
    freezing of water, 200.
    gasoline, causes of, 193.
    gasoline feed pipe, causes of, 195.
    igniter, causes of, 189, 282.
    ignition, causes of, 179.
    location of, 203.
    lubrication, 201.
    magneto, Bosch, 296.
    causes of, 183, 264, 306.
    Eisemann, 295.
    in general, 264.
    low tension, 281.
    missing explosions, 211.
    noises, 217.
    overheating, 215.
    piston ring, 198.
    secondary distributer, causes of, 192.
    spark plug, causes of, 187.
    switch, causes of, 193.
    tank, causes of, 194.
    timer, causes of, 191.
    weak explosions, 210.

  Two-cycle engine, 47,
    action of, 49.
    advantages and disadvantages of, 50.
    efficiency of, 51.

  Two-cylinder engine balance, 38.

  Two-cylinder vertical engine, disadvantages of, 42.

  Two-to-one gears, 28.

  Types of carburetors, 58.
    of timers, 98.


  Universal joints, action of, 144.
    necessity for, 144.

  Use of antiskid devices, 174.


  Valve, automatic, 25.
    action of, 26.
    adjustment of, 235.
    spring of, 27.
    check and relief, 68.
    grinding of, 226.
    leaking of, effect of, 213.
    lifter rod of, 28.
    mechanically operated, action of, 26.
    parts of, 25.
    setting of, 232.
    spring of, replacing of, 227.

  Valves, location of, 29.
    necessity for, 8.

  Vapor of gasoline, 52.

  Vehicle springs, action of, 175.

  Vibration absorbed by fly wheel, 37.

  Vibration of engines, 37.

  Vibrator, 103.

  Vibrator, adjustment of, 229.
    principle of, 105.
    contacts of, renewing of, 186.
    necessity for, 102.
    parts of, 103.
    slow, effect of, 213.

  Vibrators, mechanical and magnetic, 103.
    action of, 103.

  Voltage of storage cell, 84.

  Volts, 77.


  Warning of overheating, 216.

  Washing the car, 221.

  Water, cooling, flow of, 31.
    dirt in, 199.
    forced circulation of, 32.
    gravity system of, 34.

  Water cooling, 31.

  Water jackets, 31.

  Water pumps, 32.

  Wear of tires, 173.

  Weight of fly wheel, 42.

  Winding of primary induction coil, 93.
    of secondary induction coil, 96.

  Wires, broken, 181.
    causes of breaking, 180.

  Wiring, 236.
    for jump spark, 238.
    for make-and-break, 240.

  Wrist pin, 23.


                               THE END




                         A MOTOR-BOAT STORY.

Across Europe in a Motor-Boat.


By HENRY C. ROWLAND, author of “In the Shadow,” etc. Illustrated by
upward of fifty sketches. 12mo. Decorated cloth, gilt top, $2.00 net.

This is a delightful narrative of an absolutely unique trip. Mr.
Rowland and his two friends had a motor-boat constructed in London
for a seven-thousand-mile inland voyage which should circle Europe
by way of the Seine, the Rhine, the Danube, and the Black Sea. The
struggles with the motor, which develops a degree of perversity
almost human, the innumerable humorous and exciting incidents,
and the final terrific adventure which ends the narrative with a
shipwreck in the Black Sea, make it the most novel and entertaining
book of travel of recent years. The talented author is well known
through half a dozen books and many magazine stories. The style of
the volume is very attractive. Some fifty sketches are sprinkled
through the text.


                 D. APPLETON AND COMPANY, NEW YORK.




                       AN EXTRAORDINARY BOOK.

The Unofficial Letters of an Official’s Wife.


By EDITH MOSES. 12mo. Cloth, gilt top, $1.50 net.

This is a volume of actual letters which Mrs. Moses, the wife of
Professor Moses, wrote from the Philippines to her relatives here
in the United States. Professor Moses, who is connected with the
University of California, was one of the five members of the first
commission, of which Secretary Taft was the head, sent out by the
U. S. Government to organize the government of the Philippine
Islands. The members of this commission were practically the first
important Americans to go to the Philippines in a peaceful and a
civil capacity. Mrs. Moses, therefore, saw the social, political, and
home life in Manila as well as in the provinces and the different
islands before American civilization had entered there to any extent.
Her letters, while descriptive, have a very definite connection one
with the other. They describe the arrival at the Philippines, the
beginning of life there, housekeeping, the seemingly strange methods
of daily life, servant problems, and so on, in Manila. Nothing like
these letters has appeared in regard to the Philippine Islands at any
time. It should be borne in mind, furthermore, that these letters
are not in any way technical or having to do with the organization
of the Philippine government. They are, as the title suggests, quite
“unofficial” letters of a lady who, because of her connection with
official circles, saw many things which an ordinary traveler never
could see.


                 D. APPLETON AND COMPANY, NEW YORK.




  Transcriber’s Notes

  pg 31 Changed: thermo-siphon circulation to: thermosiphon
  pg 142 Changed: there is less change to: chance
  pg 175 Changed: chains or other anti-skid to: antiskid
  pg 272 Changed: In multi-cylinder engines to: multicylinder
  pg 272 Changed: illustration text to: Make-and-Break
  pg 280 Changed: period to comma after: be brought into use
  pg 326 Added period after: Indicated by excessive heating
  pg 326 Added period after: Defective insulation
  pg 326 Added period after: Mixture ignites
  pg 326 Added period after: Faulty adjustment of float
  pg 326 Added period after: Seconday short circuit ([1])
  pg 326 Added period after: should be from 1/64 to 1/132 inch
  pg 326 Changed: Dose cylinder with to: Douse
  pg 337 Changed: Thermo-siphon system to: Thermosiphon
  Distributor and distributer both used in text.
  Many hyphenated and non-hyphenated word combinations left as written.