1. Valve knocking, continuous knocking sound between the tail end of the valve stem and its driving parts occurs when the engine is idling, which increases with the increase of speed, and the sound does not change when the engine temperature changes or the fire is cut off;

2. Valve air leakage and valve air leakage are more obvious outside the valve room at high load and low speed. The noise increases with the increase of load. The main reason is that when the valve seat is reamed, due to improper operation or valve guide inner hole wear Too much, the valve seat is skewed or the valve gap is small, causing the valve to ablate and cause the valve to leak. Usually, we need to remove the cylinder head, grind the valve, check the elastic force of the valve spring, and readjust the valve clearance;

3. Excessive carbon deposits lead to poor valve sealing! Clean the air filter on time! Clean throttle valve! Regular maintenance! This will reduce carbon deposition.

Valve ablation leads to a decrease in the sealing performance of the valve and valve seat; the valve clearance is adjusted too small, resulting in the valve not closing tightly; the valve and valve seat cone surface carbon; when the valve is installed in the valve seat, debris is stuck, causing poor sealing; Pitting, nicks, spots, burns, and depressions on the valve working surface; poor valve sealing ring grinding during maintenance; excessive runout of valve and valve stem; excessive coaxiality of valve guide hole and seat hole, etc.

For the valve knocking caused by valve leakage, it is due to the continuous knocking sound between the tail end of the valve stem and its driving part when the engine is idling, and the sound will increase as the speed increases. The sound does not change much when the engine temperature changes or the fire is cut off. The valve leakage sound is outside the valve, which is more obvious at high load and low speed. The solution is usually to use grinding the valve and check the valve spring, the damaged and weak spring shall be replaced and the valve clearance shall be readjusted.