What engine component controls valve timing?

The engine component that controls valve timing is the camshaft.

A camshaft is a rotating shaft fitted with shaped lobes. As each lobe turns, it pushes a follower, tappet, rocker arm, or directly actuates a valve mechanism. This opens and closes the intake and exhaust valves at precisely timed points in the engine cycle.

In a conventional four-stroke engine, the camshaft turns once for every two revolutions of the crankshaft. That relationship ensures that the valves operate in step with the pistons: intake valves admit the fresh charge, and exhaust valves release combustion gases. The camshaft’s lobe shape also influences valve lift and how long each valve remains open.

The timing belt or timing chain connects the crankshaft to the camshaft, but it does not itself determine the valve profile or directly operate the valves. Modern engines may use variable valve timing, which changes the camshaft’s phase while the engine runs to improve power, efficiency, emissions, or idle quality. Some engines, including many two-stroke and rotary designs, use different mechanisms or no conventional camshaft at all.