Analysis of reasons：

（1）The abrasion or bruise of the cylinder’s surface surpasses the maximum permissible limit. This will result in the leakage and have an impact on the gas displacement.

（2）The piston and cylinder is not suitable and the gap is too big. This will result in the leakage and have an impact on the gas displacement.

（3）The cooling water in the cylinder is not good(the pipe of the cooling water has a block or the sewage in the water jacket is too much). The gas passing the valve chest to the cylinder will forms the warm-up. This will result in the leakage and have an impact on the gas displacement.

（4）The air filter is not equipped appropriately. The dirty air enters the cylinder and scratches the mirror surface.

（5） The lubricating oil in the cylinder stops or the model of the  lubricating oil is not right. This will lead to the dry friction.; There is moisture and other impurities in the oil ,which will scratches the mirror surface.

（6）There is too much incrustation in the cooling water, which is attached to the cylinder wall. This will have an impact on the cooling of the cylinder, which will make the cylinder too hot and discharge temperature too high.

（7）The piston or the piston ring has a trouble. There is a lack of lubricating oil in the cylinder. This will give rise to the dry friction and make the temperature too high.