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