Which statement best describes the cam gear speed relationship in typical engine configurations discussed?

• A. The cam gear rotates two times faster than the crank gear
• B. The cam gear rotates at half the engine speed
• C. The cam gear rotates at the same speed as the crank gear
• D. The cam gear rotates at one and a half times the engine speed

Answer: (B)

In typical four-stroke engines, the camshaft must open and close the intake and exhaust valves in precise sync with the piston’s position, and that timing relies on the camshaft turning at half the crankshaft speed. Since each valve event happens once every two crank revolutions, the timing gear or belt/chain is arranged so the cam gear has about twice as many teeth as the crank gear, giving a 2:1 ratio. This ensures one cam revolution occurs for every two crank revolutions, aligning valve timing with the piston cycle. If the cam ran at crank speed, or faster, valve timing would be off and the engine wouldn’t run correctly. Hence, the cam gear rotates at half the engine speed.