Abstract: Pistons and associated piston rings are described for use in internal combustion engines. The piston and piston ring comprise an annular piston ring groove having two radially extending walls and an axially extending wall; a compression ring received in the piston ring groove for sealing engagement with an associated cylinder wall or liner; a recess in the compression ring extending in an outwardly direction; an auxiliary sealing ring in permanent but deflectable contact with the axially extending wall of the annular piston ring groove and penetrating the recess in the compression ring; the arrangement being such that the auxiliary sealing ring does not physically limit the extent of movement of the compression ring in the annular piston ring groove. Pistons are described where two conventional compression rings are replaced by one. Test results are also presented.

Abstract: A two ring piston and piston ring assembly has an upper thin steel compression ring and a lower ring which is thicker than the compression ring and which acts both as a compression ring and an oil control ring. The lower piston ring is made of a material which is more conformable than steel, for example a plastics material, which may be reinforced. In this way, effective sealing is provided using only two piston rings, while the frictional forces between the piston and an associated cylinder are reduced.

Abstract: The detonation-resistant material is applied to a piston to reduce the likelihood of damage to the piston caused by pinking or knocking. The detonation-resistant material, which may be nickel or a nickel based material, is applied to the upper part of the ring band and around an annular portion of the crown adjacent the edge of the crown. The ring band is, before treatment, machined to form a recess extending therearound which is filled with the detonation-resistant material by a plating process. Thus, on the ring band, the detonation-resistant material does not extend radially outwardly of the remainder of the ring band. This reduces the possibility of the detonation-resistant material scraping or scuffing on the associated cylinder or liner during movement of the piston in the associated cylinder or liner and also reduces the likelihood of the detonation-resistant material being scraped off.

Abstract: A piston ring formed from a plastics material and having a maximum pressure against the associated cylinder of between 0.10 and 1.50 MN/m.sup.2 and preferably 0.50 MN/m.sup.2. One possible material for such piston rings is polyetheretherketone. The benefits obtained are greater conformability which leads to a reduction in the number of piston rings which need be used for a particular piston. This in turn reduces friction so increasing the performance of the associated engine. Acceptable wear rates and ability to withstand operating temperatures have been found in these piston rings.