Question 185Motor Plants - Assistant Engineer

The correct answer is A) one-half engine speed. In a rotary distributor type air starting system for a six-cylinder, four-stroke cycle diesel engine, the speed of the rotating distributor disc is one-half the engine speed. This is because the distributor disc needs to rotate once for every two revolutions of the engine crankshaft to properly time the air start pulses to each cylinder. The other options are incorrect because B) the same as engine speed would not provide the proper timing, C) twice engine speed would be too fast, and D) four times engine speed would be excessively fast and not aligned with the engine's four-stroke cycle.