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cylinder by suitable insulating blocks, usually made of fibre, as at Fig. 86 or Fig. 87, A, or in a fibre-lined metallic conduit, as shown at Fig. 87, D.
A typical double ignition system which has been used on some models of the Locomobile is clearly shown at Fig. 88. The method of running the wires for the primary circuit is very clearly outlined at A. The complete wiring diagram showing the high tension leads going from the magneto distributor to the spark plugs is shown at B. With a system of this kind the current may be derived from a battery which is timed by a primary circuit breaker attached to the magneto contact breaker box and sent through a single unit coil secured to the dash. The secondary current from the coil is led to the center of the magneto distributor, which serves the dual purpose of directing the high tension current from either the magneto armature or the induction coil to the spark plugs in the proper firing order. The usual method of housing the secondary cables in a conduit of insulating material so that there will be no liability of short circuiting due to oil accumulations or to contact with metal parts is so clearly shown at Fig. 87, C, that further description is unnecessary.
The repairman does not generally recognize the fact that the manner in which the high tension cables are led from a magneto or spark coil to the spark plugs is sometimes the cause of misfiring and ignition irregularities which are hard to locate. A spark may sometimes occur in a cylinder in which the piston is going down on its suction stroke which is not due to defective insulation of the wires or to short circuiting, but to an electrostatic action between one wire and a neighboring one through which no current is flowing. Endeavor should always be made to keep the secondary cables as short as possible, as in some cases if a conductor is too long the tendency is toward an unreliable spark. Some ignition experts condemn the practice of running the secondary wires close together in a fiber-lined conduit and recommend the use of fiber cleats secured to supports extending from the engine and provided with grooves that will hold the cables some distance apart.
When individual unit coils are used a condition that often puzzles those who have had no previous experience with it is what is
Fig. 88.—Wiring Diagram of Bosch Double Ignition System Used on
Locomobiles Models 38 and 48.
known among old-time repairmen as “bucking,” this usually being evidenced on engines of the four or six cylinder forms. The symptom is the same as a premature explosion in some one of the cylinders, this having a tendency to cause the engine to come to an abrupt stop. One is often led to believe that a short circuit exA
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 transformer coil. If this
magnetic influence does SCREW WIRE STRAND not go astray from its
proper confines no trouble will be experienced.
If a portion of this magSPRING TERMINAL CAP CABLE
netic field strays over
into a neighboring coil
unit enough voltage may
be induced in the secHOLE FOR BARE WIRE
ondary winding of the
latter to produce a weak INSULATED CABLE
spark at a spark plug BUTTON SPRING
connected with coil Fig. 89.–Forms of Terminals for Attachment
which rightly should reto Ignition System Cables.
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
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