Patent ID: 8789509

Claim:
A piston for an internal combustion engine, comprising: a skirt portion having an outer circumferential surface formed with surface grooves for sliding contact with a cylinder wall of the engine, the skirt portion comprising: a piston base material; and a film of lubrication coating composition defining the outer circumferential surface formed with said surface grooves and having an inner coating layer formed on a surface of the piston base material and an outer coating layer formed on a surface of the inner coating layer opposite the piston base material, wherein the outer coating layer is more susceptible to wear than the inner coating layer; wherein the piston satisfies the following dimensional condition: t2≧a−5 μm, where t2 (μm) is a thickness of the outer coating layer, and a is a groove depth (μm) of the surface grooves of the film of lubrication coating composition before wearing of the coating composition; and wherein the thickness of the outer coating layer is 3 to 6 μm.