Engine piston The piston head is the seat of the part above the piston pin, piston head of the piston ring, to prevent the high temperature, high pressure gas into the crankcase, and prevent oil from entering the combustion chamber; the top of the piston absorbed most of the heat also passed to the cylinder through the piston head, and then through the cooling medium. The piston of a large marine low-speed diesel engine is usually a crosshead type. The heat treatment process by normalizing and annealing, and iron pearlite are ferrite organization, has good heat resistance. Piston alloy quenched and tempered steel has better heat resistance and corrosion resistance. The skirt with nodular cast iron annealing treatment, with good wear resistance.