In the regular car raising process, must pay attention to check the piston, because the piston is very easy to appear problems, which is more common on the piston knocking, which is unfavorable to the health of the engine, so it should be solved early, we can check to judge whether there is a case of knocking. First, the position of the cylinder is determined by the method of cutting the oil by cylinder. If the oil is broken to a certain cylinder, the sound is obviously reduced or disappeared, and when the oil supply is restored, it can hear the obvious click sound, indicating that the cylinder piston knocks. In order to further verify the cylinder piston knockout, the injector of the cylinder can be unloaded, a small amount of CD supercharger oil is added to the cylinder, and the injector is installed, the engine is launched, the knocking sound disappears or weakened, and the rapping sound appears again for a moment, then the cylinder piston knockout is no doubt. Generally, there are many reasons for piston knocking. The main reason is that the clearance between piston and cylinder wall is too large. After the engine has been running for some time, the cylinder piston is worn out, and the lubrication is not good. The gap between the piston and the cylinder increases because of wear and tear, and a serious step appears at the bottom of the first gas ring, making the piston knock the cylinder to give out a different sound. After wearing for a certain period of time, the piston skirt and cylinder wear heavily, causing serious roundness and knocking. In addition, individual connecting rods cause deformation due to various reasons, resulting in piston eccentric wear, and larger clearance will cause knock. Piston knocking will cause excessive fuel consumption, engine oil and oil consumption. When the piston knocks badly, it also pulls the piston and breaks the cylinder. So it must be solved in time. If the cylinder head is removed and the piston is pulled out, it is found that the cylinder is seriously lost and pulled, or the gap between the piston and the cylinder is too large. The cylinder sleeve, piston and piston ring should be replaced. If the connecting rod is found to be deformed, the connecting rod should be replaced. During the driving, the engine temperature is normal, but there is a striking sound. At this time, we should pay attention to not running at high speed, and to repair it in time to avoid the delay and cause more serious damage to the engine, which leads to more serious problems.