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ists at one of the timer wires which allows a contact being made at the wrong time, producing a spark in the cylinder about to fire before the gas is fully compressed or the piston has reached top center. This is due to an inductive interference between one induction coil and a neighboring one. It is known that when the primary coil becomes energized in any unit the core becomes a magnet, and as is common with all bar magnets, lines of force are given out which run from the north to the south poles and which induce a current in the secondary winding of the

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transformer coil. If this
magnetic influence does.
not go astray from its
proper confines no trou-
ble will be experienced.
If a portion of this mag-
netic field strays
into a neighboring coil
unit enough voltage may
be induced in the sec-
ondary winding of the
latter to produce a weak
spark at a spark plug
connected with a coil
which rightly should re-
main inactive. This
condition is more noted

with old-style induction coils than with modern ones, and usually results when the motor is running slowly. The trouble has been eliminated in many of the later forms of multiple unit coils by providing anti-induction shields between the units. These are merely metallic strips in which the energies from the stray magnetic force is dissipated in the form of eddy currents instead of cutting wire layers of adjacent units. If this trouble is experienced and none of the common faults are found to exist, such as carbon deposits and rough edges in the interior of the combustion chamber or long, thin spark plug points which remain incandescent and retain heat from a previous explosion, one may suspect trouble in the multiple unit coil. It has been cured at times by inserting thin strips of sheet

iron between the coil units. The most frequent cause of "bucking" is defective insulation of the secondary wires, which allows the current to jump from one cable to another. This is sometimes found to be the case when all cables are passed closely together

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Fig. 90.-Construction of Ignition Current Switches Outlined. A-Lever · Type Magneto and Battery Switch. B-Plug Switch for Controlling One Circuit.

through a common tubular conduit, and is not apt to result when wires are carried apart in cleats, as in Fig. 87, B.

Battery Ignition System Hints.-See that the wires are heavy enough to carry the current and that all the connections are kept clean and bright as every corroded joint causes needless resistance.

Inspect battery connections etc., occasionally as they have a habit of working loose.

Look well to the ground connection, which should be very securely made and placed where it will not corrode.

Be sure the battery, especially if dry cells are used, is where it cannot get wet, as the paste-board may absorb sufficient moisture to short circuit the cells.

See that all wires are securely fastened so that they cannot by any means rub or chafe against either wood or metal parts especially the secondary wires.

Frequently examine the condition of the plugs, as troubles caused by plugs are often looked for elsewhere.

Don't allow the wires to become water- or oil-soaked, as short circuiting will probably result.

Don't screw down electrical connections with the fingers, as a tight joint cannot be made. Use pliers.

Don't allow the storage battery to get so far discharged that it will not operate the coil. See that the vibrators are set as lightly as possible to run the engine without skipping, otherwise they will waste current.

Don't take it for granted you have ignition trouble every time the engine stops.

Don't start out knowing the battery to be nearly exhausted, as it may run all right to start with, but will probably go out of business at a most inopportune time and place.

Don't adjust the coil vibrator for the biggest possible spark, as it wastes current.

Don't think a multiple unit coil is no good if the vibrators do not buzz exactly alike.

Don't test storage batteries with an ammeter unless they are charging or discharging.

Don't strain the coil by disconnecting the secondary wires completely so that no spark can jump, or by testing how far it will jump.

Don't screw or nail anything on to the coil box, as you may injure it.

Don't tolerate any loose wires or poorly made connections. Fix

them at once, using terminals for all wires as shown at Fig. 89, making sure no loose strands of wire project. Terminals should be securely soldered to wire.

Be sure all timer contacts are clean, contact points properly adjusted and distributor brushes O. K. Carbon dust in distributor will cause skipping as well oil in timer portion on points.

Don't think the ignition system will function properly with loose or dirty switch connections. Examine switch parts as shown at Fig. 90 for looseness or corrosion of contacts.

Timing Battery Ignition Systems. In timing a motor using a battery ignition system with individual vibrator coils to supply the current to respective cylinders, the first thing to ascertain is the firing order of the engine to be timed. The diagram, Fig. 91, shows all components of a battery ignition system, also a sectional view of one of the cylinders of the engine, showing the position of the piston when the spark should occur in the cylinder with the primary timer fully advanced. When the primary timer is fully retarded the spark will take place after the piston has reached the top of its stroke and has started to go down on the explosion stroke. The four unit spark coil has a two point switch on its face and has ten terminals. Four of these which are protected by heavy insulators or bushings of hard rubber run to the spark plugs as indicated. These are the secondary terminals. The two primary terminals under the switch are connected to the positive poles of the dry cell and storage batteries respectively, the negative terminals of the two batteries being joined together by a common wire and grounded. This leaves four primary leads which go to insulated terminals connecting with the segments of the timer.

The method of timing an engine is very simple. The spark advance lever on the steering wheel is advanced fully. The inlet valve of cylinder No. 1 is watched as the engine is turned by the hand crank. Just after the inlet valve closes which indicates that the piston has started to go up on its compression stroke the piston travel may be gauged accurately as it moves up by the timing rod inserted through a petcock in the top of the cylinder or through a valve cap opening. If the engine is not provided with a relief

cock or spark plug that will permit the use of the gauge rod, the flywheel markings may be utilized to determine the center corresponding to the end of the piston upward movement. The vibrator of coil connected to cylinder No. 1 should begin to buzz with the

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Fig. 91.-Simplified Wiring Diagram Explaining Methods of Timing Spark in Battery Ignition Systems.

timer casing in full advanced position before the piston reaches the end of its upward stroke. The amount of crankshaft travel is about 30 degrees from the point where the spark takes place to that where the piston reaches the top of its stroke. If the timer casing is set in full retard position the spark should take place 30 degrees of the crankshaft travel after the piston has left the

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