有的修理人员在大修发动机时，认为只要是同一型号的标准活塞和标准缸套，就可以万无一失地放心组装，其实这是一种误解。实际上，为了便于维修和选配，制造厂按照缸套和活塞的实际尺寸分成若干组，并且将分组号打印在活塞顶和缸套上口处（例如4125型柴油机的缸套、活塞分为4组 Some repair staff overhaul the engine, that as long as the same type of standard piston and standard cylinder liner, you can safely assert assembly, in fact, this is a misunderstanding. In fact, in order to facilitate repair and matching, the manufacturer is divided into several groups according to the actual size of the cylinder liner and the piston, and the group number is printed on the top of the piston and the cylinder liner (for example, cylinder liner of a 4125 diesel engine, the piston is divided into 4 groups