The piston top is a component of the combustion chamber, and is often made into different shapes. Gasoline engines often use a flat or concave top to make the combustion chamber structure compact, with a small heat dissipation area, and a simple manufacturing process. The convex piston is commonly used in two-stroke gasoline engines. The piston crown of diesel engines is often made into various pits.

The piston head is the part above the piston pin seat. The piston head is equipped with a piston ring to prevent high-temperature and high-pressure gas from entering the crankcase and oil from entering the combustion chamber; Most of the heat absorbed by the top of the piston is also transmitted to the cylinder through the piston head, and then through the cooling medium.

Editing and broadcasting of working conditions

The piston operates under conditions of high temperature, high pressure, high speed, and poor lubrication. The piston is in direct contact with high temperature gas, and the instantaneous temperature can reach more than 2500K. Therefore, the piston is seriously heated and the heat dissipation condition is poor, so the temperature of the piston during operation is very high, up to 600~700K at the top, and the temperature distribution is very uneven; The top of the piston bears a large amount of gas pressure, especially the maximum working stroke pressure, which can reach as high as 3-5 MPa for gasoline engines and 6-9 MPa for diesel engines. This causes the piston to have an impact and bear the effect of lateral pressure; The piston moves back and forth in the cylinder at a high speed (8-12 m/s), and the speed is constantly changing, which generates a large inertial force, causing the piston to be subjected to a large additional load. When the piston operates under such harsh conditions, it will deform and accelerate wear, as well as generate additional loads and thermal stresses, while also being subjected to chemical corrosion from gas.

Piston inspection mainly includes measurement of skirt diameter, piston ring groove height and piston pin seat hole size:

① The selection of pistons should be determined according to the repair size of the cylinder. Usually, the size value is increased and marked on the piston crown;

② In the same series of fish feeding clusters, the piston structure may not necessarily be the same. Therefore, when selecting pistons, the corresponding type of piston must be selected based on the type of engine. On the same engine, pistons of the same brand, group, or product code should be selected; The same model must use pistons with the same product code to ensure that the difference in piston diameter and quality does not exceed the range specified by the original factory. Otherwise, it may cause engine combustion problems, rough operation, reduced economy and power performance, etc. Therefore, when selecting pistons, the corresponding model of piston must be selected based on the type of engine.