IC engine spark advance and retard mechanism - has pair of springs opposing centrifugal effect which cause rotation of upper plate w.r.t. baseplate

摘要

The ignition spark advance and retard mechanism minimises the effects of the tolerance spread of springs normally used in the timing arrangement and maintains the spark timing within the phase - speed band defined by the engine designer. The mechanism is driven from the normal engine timing shaft central within the distributor casing and carries a base plate with two diagonally opposite vertical axis pins for a pair of crescent shaped elements (5a,5b) facing inwards. The ends of the elements are held apart by two rollers (7) which are mounted on a 'Z' shaped plate (6) on a shaft (8) in - line with the timing shaft. Centrifugal forces alters the relative position of the upper and base plates the movement being restrained by a pair of springs between them.