Pressurized lubricating oil is accumulated in the bearings of opposed pistons and accumulated oil is dispensed therefrom for bearing lubrication and also for cooling the undercrowns of the pistons by jets of oil emitted from the bearings.

A method for coating a surface of a closed cooling channel, having a plurality of oil supply bores and a plurality of oil discharge bores, of a piston for an internal combustion engine, having a coating medium containing hexagonal boron nitride may include introducing a defined quantity of a coating medium comprising a suspension of hexagonal boron nitride with a solution on a basis of at least one thermally curable inorganic binder and at least one solvent into the cooling channel, spreading the coating medium over the surface of the cooling channel by moving the piston about at least two spatial axes, using a laminar air flow to dry the coating medium spread over the surface of the cooling channel, and thermally curing the coating medium to complete a coating adhering to the surface of the cooling channel.

A piston for an internal combustion engine is formed from an upper part connected to a lower part. The upper part has a combustion bowl, a top land, and a ring belt extending circumferentially around the piston upper part. The lower part contains pin bosses and a piston skirt. A circumferential cooling channel is formed by joining the upper and lower parts. There is an oil inlet formed in one piece with the piston lower part. The inlet has a lower extremity and an upper extremity that terminates at the floor of the cooling channel. A bore extends through the oil inlet from the lower extremity up though the floor of the cooling channel. The circumference of the bore increases from the upper extremity to the lower extremity, so the oil inlet forms a funnel shape.

An internal combustion engine piston having a cooling chamber open to in a direction toward of pin boss bores. In one example, a shaft separates an inner form of a cooling chamber and a cooling pocket. A transfer hole allows passage of a cooling oil between the inner form and the cooling pocket or several cooling pockets. In one example when the piston is at a bottom dead center position, a cooling oil nozzle is directed toward the transfer hole and when the piston is at a top dead center position, the cooling oil nozzle is directed to a hub region of the cooling chamber.