The top of the piston is in direct contact with the high-temperature gas, which makes the temperature of the top of the piston very high. The piston slides at high speed along the cylinder wall under the action of lateral pressure. Due to poor lubrication conditions, friction loss is large and wear is serious. Generally speaking, about 40% of the friction loss on Bare Engine comes from the friction between the piston, piston ring and cylinder wall, not the car.

The function of the connecting rod group is to transfer the force borne by the piston to the crankshaft, and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The connecting rod group is subjected to alternating loads of compression, tension and bending during operation, so the connecting rod body may bend and twist. The connecting rod body and connecting rod cap are made of high-quality medium carbon steel or medium carbon alloy steel die forging or roll forging.

The crank-connecting rod mechanism consists of a piston-connecting rod group, a body group and a crankshaft flywheel group. It is a transmission mechanism for an internal combustion engine to realize the working cycle and complete energy conversion. It is an energy conversion mechanism for Mitsubishi Engine, through which the heat energy generated after fuel combustion is converted into mechanical energy. Its working conditions are quite bad, it should withstand high temperature, high pressure, high speed and chemical corrosion, as well as large air pressure and mass inertia of moving parts. Therefore, the material and structure requirements of the crank-connecting rod mechanism are quite high, and its structure directly determines the performance and efficiency of Bare Engine.