Bánh răng cam

A camshaft is the shaft with shaped lobes that opens and closes the engine's valves in time with the pistons.

As it rotates, its lobes push the valve train so each valve opens at exactly the right moment for intake and exhaust; timing gears or chains keep it synchronized with the crankshaft.

The camshaft runs in the engine block or cylinder head. The correct camshaft matches the engine model and valve timing.