The piston function is to transform the thermal energy developed in the combustion into mechanical energy through the reciprocating motion inside cylinders. They must be able to withstand the extreme conditions which exist within it. The piston also should be light to avoid passing on excessive inertia to increase engine vibration and be able to provide sealing the cylinder so that the gases do not escape impairing the operation of the engine.
The pistons are cast in one piece and can be made of cast iron, steel and aluminum alloys. Cast iron piston less wear and can be used with fewer gaps due to expand less than aluminum. Instead of aluminum pistons are much more light and have a heat transfer coefficient greater. Therefore piston engines employing casting require more cooling water and cooling jackets plates of reduced thickness. The piston can be made in her head in her lap material and be constructed in another to join in one piece thanks to a weld.
The piston head is responsible to withstand the high pressures and temperatures while the skirt has the function of transmitting the motion to the crank. Requires binding of a bearing so that it can transmit the movement without excessive friction.