The working principle of the piston connecting rod mechanism is to convert the pressure of the gas acting on the top of the piston into the power that can make the crankshaft rotate and output externally. During the engine's working process, the gas pressure generated by fuel combustion acts directly on the top of the piston, pushing the piston to move in a reciprocating linear motion. Through the piston pin, connecting rod, and crankshaft, the reciprocating linear motion of the piston is converted into the rotational motion of the crankshaft.

The composition of the piston connecting rod group is as follows:

Piston. The main function of the piston is to bear the gas pressure in the cylinder and transfer this force to the connecting rod through the piston pin to drive the crankshaft to rotate. It transmits the pressure of the combustion gas to the crankshaft, causing the crankshaft to rotate and output power. The top of the piston also forms the combustion chamber together with the cylinder head and cylinder wall.

Piston rings. Piston rings include gas rings and oil rings. When the piston rings are working, they are subjected to the high temperature and high pressure of the gas in the cylinder, their temperature is relatively high, and they move at high speed in the cylinder. Coupled with the high-temperature deterioration of the engine oil and the deterioration of the lubrication conditions, their wear is severe. After the piston rings wear out and fail, the engine has difficulties in starting, insufficient power, increased pressure in the crankcase, large consumption of engine oil, black smoke from the exhaust, and severe carbon deposits on the piston edges.

Piston pin. The function of the piston pin is to connect the piston and the small end of the connecting rod and transfer the force exerted by the gas on the piston to the connecting rod. The piston pin is a hollow cylinder, generally made of low-carbon steel, low-carbon alloy steel carburized and quenched or high-frequency quenched with No. 45 medium-carbon steel.

Connecting rod. The function of the connecting rod is to connect the piston and the crankshaft, convert the reciprocating motion of the piston into the rotational motion of the crankshaft, and transfer the force borne by the piston to the crankshaft.