A six-cylinder, four-stroke/cycle diesel engine is fitted with a rotary distributor type air starting system. The speed of the rotating distributor disc is __________.

Correct Answer: Option A — one-half engine speed

A four-stroke cycle engine completes one power stroke per cylinder every two crankshaft revolutions (720 degrees). Therefore, a rotary distributor governing starting air admission must rotate at exactly half engine speed to synchronize properly with the operating cycle.