Valve timing — Camshaft-to-crankshaft speed in a four-stroke engine In a conventional four-stroke engine, for each one revolution of the crankshaft, how much does the camshaft rotate?

Introduction / Context:The camshaft opens and closes intake and exhaust valves in sync with piston strokes. In four-stroke engines, the valve events repeat every two crankshaft revolutions, which defines the cam-to-crank speed relationship.

Given Data / Assumptions:

• Four-stroke Otto or Diesel engine.
• Fixed cam drive via gears, chain, or belt.

Concept / Approach:One complete engine cycle requires two rotations (720 degrees) of the crankshaft: intake, compression, power, and exhaust. The camshaft lobes must complete their open/close sequence once per cycle, so the camshaft must rotate at exactly half the crankshaft speed.

Step-by-Step Solution:Engine cycle = 2 crank revolutions = 720 degrees.Cam lobes repeat once per cycle → camshaft rotates 360 degrees per 720-degree crank cycle.Therefore, for each 1 crank revolution, camshaft turns 1/2 revolution.

Verification / Alternative check:Timing gears or sprockets use a 2:1 ratio; service marks align accordingly.

Why Other Options Are Wrong:One turn/two turns/four turns: would desynchronize valve timing.One-quarter turn: not consistent with 2:1 ratio.

Common Pitfalls:Confusing two-stroke and four-stroke timing relationships.

Final Answer:one-half turn