Fig. 60. Bosch M Distributor and Interruptor—Housing Removed

[Fig. 61] shows a circuit diagram of the Type ZR. Ed. 16. Bosch Magneto. Note that the spark plugs must be connected up in accordance with the firing order of the engine. The metal segments imbedded in the distributor plate are connected with the terminal studs on the face of the plate, and the latter are connected by cable to the spark plugs in the various cylinders. In the cylinders the high tension current produces a spark which produces ignition, and then returns through the ground and the engine to the magneto armature, thus completing the circuit.

Timing the Magneto.—With the average four cycle engine the proper operating results are obtained by timing the magneto as follows: The crank shaft is rotated to bring the piston in No. 1 cylinder (in automobile practice this is the cylinder nearest the radiator) exactly on top dead center of the compression stroke. The timing control lever on the housing is then placed in the fully retarded position. With this done, the magneto distributor plate should be removed by withdrawing the two holding screws, or by releasing the two holding springs as the case may be.

DISTRIBUTOR
BRUSH
HOLDER		SAFETY
SPARK GAP
SLIPRING CONDENSER
ARMATURE INTERRUPTER
GROUND GROUND

Fig. 61. Wiring Diagram Bosch Magneto, Type ZR-4

The operation of the platinum contact points is controlled by the action of the interruptor lever as it bears against the two steel segments secured to the inner surface of the interruptor housing.

In [Fig. 60], A shows the distributor with the face plate removed to show the position of the distributor segments which are connected to the terminal posts on the back of the plate. B shows the interruptor housing and cover removed from its position on the magneto. C shows the complete assembly of the distributor and interruptor. Note that the face plate of the distributor is fastened on with a set of screws while the interruptor cover is held in position with a latch.

The Secondary or High Tension Current.—The high tension current is generated in the secondary circuit only when there is an interruption of the primary circuit, the spark being produced at the instant the platinum interruptor contact points separate. The armature secondary circuit is a continuation of the armature primary circuit, the beginning of the secondary circuit being connected to the primary, while the end of the secondary is connected to the insulated current collector ring mounted on the armature just inside the driving shaft end plate of the magneto. The slip ring brush is held in contact with the slip ring by a brush holder at the shaft end of the magneto which receives the high tension current collected by the slip ring by means of a connecting bar which passes under the arch of the magnets, and passes the current to the center of the distributor plate, thus exposing the distributor brush and gear. The cover of the interruptor housing is also to be removed to permit observation of the interruptor points.