Pistons and cylinder liners

An internal combustion engine comprising a cylinder having an untreated cylinder wall of an aluminum alloy and a piston mainly composed of an aluminum alloy, the piston comprising a crown, a ring band integral with the crown and having grooves therein for the reception of piston rings, a skirt integral at its upper end with the ring band and having a running surface having opposed portions which form opposed thrust faces for engagement under pressure with the wall of the cylinder, and at least one expansion-control insert of ferritic steel, the insert being mounted in the skirt, a portion of the insert forming a portion of the running surface of the skirt of the piston, said portion of the insert being confined to an upper portion of the skirt and within the opposed thrust faces of the piston.