Synchronous Drive

—In gas engine ignition, a high tension magneto must be driven ‘‘synchronously,”’ which is to say, at a speed in ratio to that of the engine, generally at one half engine speed for a four-cylinder engine, in order that the spark may always occur at precisely the proper point in the rotation of the armature. The drive may be by toothed wheel gear or chain and sprocket. The friction gear drive or belt and pulley are alike objectionable, from the fact_that no slipping or variation is permi ible. While some recent forms of high tension magneto operate asynchronously, the common types are ‘so made that the spark shall occur in the first cylinder at precisely the moment the magneto armature is at a certain point in its rotation. If, therefore, this condition be not strictly observed, the spark will be of defective intensity, and the control of the engine complicated.