The piston assembly transfers the force from the power stroke to the crankshaft. Its design depends on the type of engine, its speed and compression ratio.
Piston rings keep a tight seal within the cylinder to stop the heat and pressure in there from escaping. They also stop oil passing up into the combustion chamber.
The connecting rod joins the piston to the crankshaft. It is fastened to the piston at its little-end by a piston pin, or gudgeon. It must be very strong, rigid, and as light as possible.
