The piston operates under conditions of high temperature, high pressure, high speed, and poor lubrication. The piston is in direct contact with high-temperature gases, with instantaneous temperatures reaching over 2500K. Therefore, it experiences severe heating, while heat dissipation is very poor. As a result, the piston operates at very high temperatures, reaching 600-700K at the top, and the temperature distribution is highly uneven. The piston top bears significant gas pressure, especially during the power stroke, reaching 3-5 MPa in gasoline engines and 6-9 MPa in diesel engines. This causes the piston to experience impact and lateral pressure. The piston reciprocates at a very high speed (8-12 m/s) within the cylinder, and this speed is constantly changing, generating significant inertial forces and subjecting the piston to substantial additional loads. Operating under these harsh conditions, the piston deforms and wears faster, incurs additional loads and thermal stress, and is also subjected to chemical corrosion from the combustion gases.
Piston inspection mainly involves measuring the skirt diameter, piston ring groove height, and piston pin seat bore size:
① Piston selection should be determined according to the cylinder's repair dimensions. The oversized dimensions are usually marked on the piston top;
② Within the same series of pistons, their structures may differ. Therefore, when purchasing pistons, the corresponding type must be selected based on the engine type. For the same engine, pistons from the same brand, group, or product code should be used; pistons of the same product code must be used for the same engine model to ensure that the difference in piston diameter and mass does not exceed the original manufacturer's specifications. Otherwise, it may cause poor engine combustion, rough operation, and reduced fuel economy and power. Therefore, when selecting pistons, the corresponding model must be chosen based on the engine type.
