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 transmit 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 by die forging or roll forging.

The piston connecting rod group, the body group, and the crankshaft flywheel group together form the crank-connecting rod mechanism, which is the transmission mechanism for the internal combustion engine to realize the working cycle and complete the energy conversion. It is the mechanism for Mitsubishi Engine to generate and transmit power. Through it, the heat energy generated after the fuel is burned is converted into mechanical energy. It is the energy conversion mechanism of Mitsubishi Engine.

Its working conditions are quite harsh. It has to withstand high temperature, high pressure, high speed and chemical corrosion, as well as great gas pressure and the mass inertia force of moving parts. Therefore, the material and structural requirements of the crank-connecting rod mechanism are quite high. Its structure directly determines the performance and efficiency of Bare Engine.