Which statement about cam gear speed is correct?

Which statement about cam gear speed is correct?

• 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 a four-stroke engine, the camshaft must complete one revolution for every two revolutions of the crankshaft to keep valve timing correct. That setup comes from the need for each valve to open and close once during each engine cycle, which spans two crank revolutions. The gearing is arranged so the cam gear rotates at half the crank speed, typically with twice as many teeth on the cam gear as on the crank gear. This half-speed relationship ensures valves open and close in proper sync with piston position. So the statement that the cam gear rotates at half the engine speed is the correct description. If the cam rotated faster or at the same speed as the crank, or at 1.5 times the engine speed, the valve events would misalign with the piston’s movements, causing timing issues and potential engine problems.

In a four-stroke engine, the camshaft must complete one revolution for every two revolutions of the crankshaft to keep valve timing correct. That setup comes from the need for each valve to open and close once during each engine cycle, which spans two crank revolutions. The gearing is arranged so the cam gear rotates at half the crank speed, typically with twice as many teeth on the cam gear as on the crank gear. This half-speed relationship ensures valves open and close in proper sync with piston position.

So the statement that the cam gear rotates at half the engine speed is the correct description. If the cam rotated faster or at the same speed as the crank, or at 1.5 times the engine speed, the valve events would misalign with the piston’s movements, causing timing issues and potential engine problems.