08/20/2026
How Does the Camshaft Open Each Valve at the Right
Time?
Inside a running engine, the pistons move thousands of times per minute, but the valves must open and close at exactly the right moment. So, how does the engine know when to open them?
The answer is the camshaft.
The camshaft has specially shaped lobes called cams. As it rotates, each cam pushes a valve mechanism, opening the intake or exhaust valve at a precise moment.
When the cam moves away, the valve spring pushes the valve closed again.
The interesting part is that the camshaft is mechanically synchronized with the crankshaft. In a conventional four-stroke engine, the crankshaft makes two complete rotations for every one rotation of the camshaft.
This precise timing allows the engine to take in fresh air, compress the mixture, produce combustion, and release exhaust gases in the correct sequence.
The cycle is:
Crankshaft → Timing chain/belt → Camshaft → Cam lobes →
Valves → Engine combustion.
All of this happens incredibly fast, with the camshaft controlling the engine’s breathing every second the engine is running.
