Why is valve clearance necessary?
1 Answers
Valve clearance is set to ensure the normal operation of the internal combustion engine's valve train. Since the valve train operates at high speeds and elevated temperatures, the valves will expand due to heat. If there is no clearance or insufficient clearance between the valve and its transmission components when cold, it can cause gas leakage during the compression and power strokes, leading to reduced engine power and, in severe cases, difficulty in starting. To prevent this phenomenon, a certain clearance is intentionally left between the end of the intake/exhaust valve stem and the adjusting screw of the tappet (or rocker arm) during the design of the valve train, compensating for the thermal expansion of the valve. Below is relevant information about valve clearance: Valve clearance size: The valve clearance is generally determined by the engine manufacturer through experiments. Typically, when cold, the intake valve clearance is 0.25–0.30mm, and the exhaust valve clearance is 0.30–0.35mm. If the clearance is too small, the engine may experience gas leakage when hot, resulting in power loss or even valve burning. If the clearance is too large, impacts may occur between transmission components and between the valve and valve seat, causing unstable operation of the entire valve train, increased noise, and reduced valve opening duration, leading to insufficient intake and exhaust.
