These magnetos run in only one direction. This running direction should be given when magneto is ordered, as being “clockwise” or “counter-clockwise” when looking at the driving end of the magneto.
The magneto for the single and double cylinder engines has no distributor, the high tension current being led directly from the armature.
The circuit diagram of the Bosch four cylinder magneto is shown by Fig. 108, the winding and plug connections being clearly shown. When connecting the magneto care should be taken to have the distributor and plug connections arranged so that the cylinders will fire in the proper order.
(101) Bosch Oscillating High Tension Magneto.
The oscillating type of magneto is used on slow speed heavy duty engines that move too slowly for the ordinary type of magneto. In the oscillating type the armature is given a short angular swing by the action of a tripping device operated by the engine which results in an intense spark at the lowest speeds.
Magneto type “29” is constructed with two powerful steel magnets, while magneto type “30” is provided with three; an armature of the shuttle type is arranged to oscillate between their pole-shoes.
The magneto is actuated by a rotating cam or other suitable device, which moves the armature 30° from its normal position whenever ignition is required. To permit this movement, a trip lever is mounted upon the tapered end of the armature shaft, this trip lever being held in a definite position by the tension of the spring or springs 1. The trip lever is only supplied when specially ordered, but each magneto is provided with the necessary springs and spring bolts.
When the trip lever is moved from its normal position by the operating mechanism, the springs are extended, and when the operating mechanism releases the trip lever, the later returns the trip lever and armature to their normal position, this movement resulting in the production of a sparking current in the armature winding.
The winding of the armature is composed of two parts, one being the primary winding, which consists of a few turns of heavy wire, and the other the secondary winding, which consists of many turns of fine wire.
The tension of the current produced by the oscillation of the armature is increased by closing the primary circuit at a certain position in its movement, and then interrupting it by means of the breaker. At the moment of the interruption, an arc-like spark is formed at the spark plug and ignition occurs.