The middle octagon connecting rod on the engine is a part of the crank connecting rod mechanism and a part of the piston connecting rod group. This is the part with extremely high technical content in the engine, which has extremely high requirements on the material, metallurgical process and heat treatment of parts, especially the piston and piston ring, which directly affects the service life of the engine.

The main function of the piston connecting rod group is to receive the combustion gas pressure, and transmit this force through the piston pin to the Middle octagon connecting rod and then to the crankshaft, and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. It can also be subdivided into piston groups and connecting rod groups.

The main function of the piston is to withstand the combustion gas pressure and transmit this force to the Middle octagon connecting rod through the piston pin to push the crankshaft to rotate. The function of the Middle octagon connecting rod group is to transmit the force of the piston to the crankshaft and convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The Middle octagon connecting rod group is subjected to alternating loads such as compression, tension, and bending during work, so the middle octagon connecting rod body may be bent and twisted. The connecting rod body and the connecting rod cover are made of high-quality medium carbon steel or medium carbon alloy steel by die forging or roll forging.

The piston Middle octagon connecting rod group, the body group, and the crankshaft flywheel group together form the crank connecting rod mechanism. It is the transmission mechanism for the internal combustion engine to realize the working cycle and complete the energy conversion. It is the mechanism for the engine to generate and transmit power. It burns the fuel. The heat energy is converted into mechanical energy, which is the energy conversion mechanism of the engine. Therefore, the material and structure requirements of the Middle octagon connecting rod mechanism are quite high, and its structure directly determines the performance and efficiency of the engine.