What is a camshaft?

• A. A long bar with egg-shaped eccentric lobes, one lobe for each valve and fuel injector
• B. A short rod with gear teeth
• C. A belt-driven pulley
• D. A device to damp vibrations

Answer: (A)

The camshaft is the shaft that carries the shaped lobes used to open and close the engine’s valves at the correct times. Each lobe is egg-shaped so as it rotates, it rides against a follower or rocker arm to lift a valve open, then release it to close as the lobe moves on. In many engines there’s a separate lobe for each valve (and in some designs also for each fuel injector), which is why the description mentions lobes for valves and injectors. The other options point to different parts: a short rod with gear teeth would be a pinion or part of a gear train, a belt-driven pulley is just a drive pulley rather than the camshaft itself, and a device to damp vibrations refers to a damper or harmonic balancer.