MAGNETO AND IGNITION SYSTEM
A magneto that is kept clean and properly oiled rarely gives trouble, and it is a mistake to blame it whenever the engine runs irregularly or will not start. Its adjustments should be changed only when the other parts of the engine have been proved to be in good condition.
The working parts of a magneto are enclosed, and practically proof against dust. It should be wiped off frequently, and dust and grit should not be allowed to collect around the oil holes, for otherwise it will work into the bearings and damage them.
Dust and dirt are especially injurious to the circuit breaker, which should be frequently inspected and cleaned. Very little oil should be used on it, and this should be the light oil used for typewriters and sewing machines. A thicker oil will become gummy, and will prevent the free action of the lever.
If there is much sparking at the platinum points, so that they become corroded and rough, it is an indication that the condenser of the magneto is not operating as it should, for the object of the condenser is to prevent such sparking. The only remedy is to renew the condenser.
Rough points will spark more than smooth ones; should they get into this condition, they should be lightly filed with a file of the cut known as “dead smooth.” If this file cannot be obtained, pinch a strip of the finest sand paper—not emery paper—between the points, and draw it gently back and forth, smoothing down first one point and then the other. In smoothing platinum points the greatest care should be taken to make them flat and true to each other.
After smoothing the points they should be readjusted so that when they are separated by the cam they are from ¹/₃₂ to ¹/₆₄ inch apart.
A distributor made with a carbon brush that slides across the contacts will require wiping off at least once a month. Carbon dust will rub off the brush and collect on the face of the distributor; in the course of time this will cause a short-circuit. The distributor is always made so that it can easily be cleaned.
A magneto is timed to an engine so that when the spark control is fully retarded, the circuit breaker points are just separating as a piston goes over top center. The engine is cranked until one of the pistons is at top center; the magneto should be in position, but its coupling should be loose, so that the armature can be revolved. The spark control is retarded; that is, it is moved as far as possible in the direction in which the armature turns. The armature is then revolved in the direction in which it will be driven by the engine until it is seen that the contact points are beginning to separate; holding the armature, the coupling is then made fast.
It will now be found that the distributor brush is touching one of the contacts; that contact is to be connected with the spark plug of the cylinder that is at top center of the compression stroke. The following distributor contacts are connected to the remaining spark plugs in the order in which their cylinders fire.
Should the magneto be suspected of being out of order, the first test is to disconnect a wire from its spark plug, and support the tip ⅛ inch from the metal of the engine while the engine is cranked briskly; if a spark appears, it is evidence that the magneto is operating and that the trouble is elsewhere.
If there is no spark, repeat the test with the switch wire disconnected from the magneto. This wire and the switch form a circuit from the metal of the engine to the insulated part of the circuit breaker; when the switch is closed, or in the “off” position, this circuit is completed, and as the magneto current flows over it instead of over the regular sparking circuit, no spark is produced at the plug. It sometimes happens that the switch or wire is defective, and allows the current to take that circuit even when the switch is in the open or “run” position. If this is the case it will be shown by a spark on cranking the engine with the switch wire disconnected at the magneto, and no spark when it is connected.
If the switch and wire are all right, examine the circuit breaker to see whether the contact points are clean, and that they touch when the cam allows them to; touch the circuit breaker lever to see that it is free to move and that its spring is not broken. In some tractors the magneto is in such a position that the circuit breaker cannot easily be seen; in such a case hold a small mirror in front of the circuit breaker and examine the reflection.
If the circuit breaker is in good condition, examine the distributor to see whether it is dirty, or the brush broken; if these parts are all right, the trouble is of such a character as requires the magneto to be returned for repair.
Ignition trouble is usually in the spark plugs. The insulator cracks easily in many makes, which will permit the current to leak across without forming a spark; it is frequently the case that the crack does not show, and the best test is to replace the suspected plug with a plug that is known to be good. If the cylinder fires with one plug and not with the other, there is no question as to the cause of the trouble.
The insulator of the plug must be kept clean, for a deposit of carbon on it will form a path by which the current can pass without forming a spark. A dirty plug can best be cleaned by brushing it with a stiff toothbrush dipped in gasoline. A carbon deposit can be softened by soaking the plug in gasoline for a few hours, and can then be brushed off more easily.
The spark gap of a plug should be from ¹/₃₂ to ¹/₆₄ inch. After considerable use the points will be burned off, and the gap will become too wide; the points should then be bent to form a proper gap.
Oil and grease will rot rubber, and the ignition wires should therefore be wiped clean. Oil-soaked cables will give trouble, and should be replaced with new ones.
It is frequently difficult to locate a leakage of current. If the engine is misfiring and losing power, and a leakage of current through poor insulation is suspected, the easiest way to detect it is to run the engine in the dark. Leaks will show themselves by sparks, which are then easily seen.