Abstract: A composite valve seat has a valve spot surface zone made of a second sintered alloy which is a special sintered alloy and the remainder of the valve seat is made of a first sintered alloy which is an ordinary low-alloyed sintered alloy. A boundary between the first and second sintered alloys describes a curve which is, with the valve spot surface oriented upward, highest at an outer peripheral surface of the valve seat. The curved boundary gradually falls toward an inner peripheral surface of the valve seat and the shape of the curved boundary is similar to the powder rest curve of the first sintered alloy.

Abstract: A powder compression molding method for producing a multilayer powder compression molded article having a plurality of different material layers disposed in a compression direction utilizes relative movements between an upper punch, a lower punch, a die having a step formed therein, and two feed shoes. The powder compression molded article thus formed requires a reduced amount of a special layer. The powder compression molding method includes forming a first space by moving the die relative to the lower punch, introducing a first powder into the first space through a first feed shoe, lowering the lower punch relative to the die to form a second space so that an upper surface of the first powder on the step of the die and on the lower punch has a nonuniform height, introducing a second powder into the second space, and moving the upper punch towards the lower punch to compress the first and second powders.

Abstract: A piston ring produced by a powder metallurgical method has a nearly triangular zone in cross section made of a low density sintered alloy metal powder. One edge of an outer peripheral surface or bottom surface of the piston ring forms a vertex of the triangular zone. The remainder of the piston ring is composed of a high density sintered alloy metal powder. This piston ring has a high abrasion resistance at the area thereof which slides on the cylinder wall and can be produced at low cost.

Abstract: A corner seal member for use in a rotary internal combustion engine is constructed with an apex seal groove and an elongated cavity. The elongated cavity forms a thin wall having a substantially semicircular cross-section in the opposite side of the apex seal groove. The gas pressure delivered into the elongated cavity is advantageously used for urging the corner seal towards the inner surface of the corner seal groove, thereby preventing the gas pressure from leaking into an adjacent working chamber.