The pistons and connecting rods on Bare Engine are part of the crank-connecting rod mechanism, and together they form a piston-connecting rod group. It is a component with extremely high technical content in Mitsubishi Engine, and has extremely high requirements for the materials, metallurgical processes, heat treatment, etc. of the parts, especially the pistons and piston rings, which are directly related to the service life of Bare Engine.

The main function of the piston-connecting rod group is to be subjected to the pressure of the combustion gas, transmit this force to the connecting rod through the piston pin, and then to the crankshaft, converting 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 pressure of the combustion gas and transmit it to the connecting rod through the piston pin to promote the rotation of the crankshaft. In addition, the top of the piston forms a combustion chamber together with the cylinder head and cylinder wall. The piston is a component with strict working conditions in Bare Engine. Gas force and reciprocating inertia force on the piston.