What is the valve clearance?What is the harm of being too big or too small?
Valve clearance:
When the valve is fully closed, the clearance between the end of the valve stem and the parts of the valve drive set is called the valve clearance.
Necessity of valve clearance:
When the engine is working, the valve will expand due to the temperature rise. If there is no gap or the gap between the valve and its driving parts is too small in the cold state, the expansion of the valve and its driving parts will inevitably cause the valve to close loosely in the hot state, resulting in air leakage during the compression and power stroke of the engine, resulting in power reduction, and even difficult to start in serious cases. In order to eliminate this phenomenon, the valve clearance is usually reserved when the engine is cold assembled to compensate for the expansion of the valve after heating. Some engines use hydraulic tappets. The length of the tappets can automatically change at any time to compensate for the thermal expansion of the valve, so it is not necessary to reserve the valve clearance. The valve clearance shall be determined by the engine manufacturer according to the test. Generally, in the cold state, the inlet valve clearance is 0.25mm~0.35mm, and the exhaust valve clearance is 0.30mm~0.35mm, which is too small: the valve clearance is too small, and the engine may leak due to the valve closing is not tight in the hot state, resulting in power reduction and even valve burning. Oversize: excessive valve clearance will cause impact noise between transmission parts and between valve and valve seat, and accelerate wear. At the same time, the duration of valve opening will be reduced, and the inflation and exhaust of the cylinder will become worse.
