The connecting rod group is composed of connecting rod body, connecting rod big head cover, connecting rod small head bushing, connecting rod big head bearing bushing and connecting rod bolt (or screw). The connecting rod group is subjected to the gas force from the piston pin, its own oscillation and the reciprocating inertia force of the piston group, the magnitude and direction of these forces are periodically changed. Therefore, the connecting rod is subjected to alternating loads such as compression and tension. The connecting rod must have sufficient fatigue strength and structural stiffness. Insufficient fatigue strength will often cause the connecting rod body or connecting rod bolt to break, and then produce a major accident of the whole machine damage. If the stiffness is insufficient, it will cause the bending deformation of the rod body and the circular deformation of the big head of the connecting rod, resulting in the partial wear of the piston, cylinder, bearing and crank pin.
The connecting rod body is composed of three parts, and the part connected with the piston pin is called the connecting rod small head; The part connected with the crankshaft is called the big head of the connecting rod, and the part connecting the small head and the big head is called the connecting rod body.