Piston is one of the most important movable components in an engine. It provides the required vacuum pumping (intake stroke) for fuel-air mixture in engine cycle to fill into the cylinder and compressing (compression stroke) to generate the required pressure for the mixture's self ignition by making use of inertial power of crank shaft. The chemical energy generated by ignition and explosion of compressed mixture is converted to rectilinear motion by the piston (power stroke) and the engine is powered up. The exhaust gases remaining in the cylinder as a result of ignition in the power stroke are swept (by boosting) and evacuated at exhaust by the piston by making use of inertial power of crank shaft (exhaust stroke).
Rectilinear motion facilitated in the power stroke is converted to rotational motion expected from engine by piston pin, connecting rod and crank shaft. Aluminum is preferred today as the piston material having the advantages such as providing heat conductivity, being pretty light, easy-to-cast and process. When the piston is at the working temperature, it is designed by calculation the expansion during the processing (when cold) to make it full cylinder. For this purpose, the extreme expansions should be taken under control by processing cross sections on the piston at various diameters and oval shapes according to their material density and the temperature values to be exposed.