Timing Components: Description and Operation

VALVE TIMING





Engines are designed so the valves open slightly before the beginning of the stroke and close slightly after the end of the stroke - in this way the valve will open long enough to provide good engine power.

Because it takes times for the valves to open fully and close, there is a short time when the exhaust valve is still closing and the intake valve has already started to open. This "valve overlap" time is minimized in modern engines to reduce HC emissions.

For any four stroke cycle piston engine to operate efficiently, the intake and exhaust valves must open "in time" with each piston intake and exhaust stroke.

Incorrect valve timing will cause poor engine performance and excessive exhaust emissions.