Camshaft

The camshaft is a precision-engineered rotating shaft that controls the timing and lift of the engine's intake and exhaust valves. Located either in the engine block (in pushrod engines) or on top of the cylinder head (in overhead cam, or OHC, engines), the camshaft features egg-shaped lobes along its length. As the shaft rotates, these lobes push down on the valves (either directly or through lifters and rocker arms) to open them, allowing fresh air-fuel mixture in and spent exhaust gases out.

The rotation of the camshaft is mechanically synchronized with the crankshaft via a timing belt, timing chain, or timing gears. For every two complete rotations of the crankshaft, the camshaft rotates exactly once. This synchronization is crucial: if the timing is off by even a fraction of a second, the valves will not open at the correct times, resulting in poor engine performance, misfires, or catastrophic internal engine damage if the pistons strike the open valves.

Camshafts can wear down over time due to oil starvation, dirty engine oil, or normal high-mileage fatigue, flattening the lobes and preventing the valves from opening fully. Symptoms of a worn camshaft include a ticking or tapping noise from the top of the engine, rough idling, power loss, and engine misfires. Replacing a camshaft involves removing the valve covers, timing components, and lifters to swap in a new shaft.