The present disclosure discloses an apparatus (100) for eliminating slack and vibrations of the chain (400) comprising a piston-cylinder arrangement. A first piston (10) is configured to be displaced inside the cylinder (20) of the piston-cylinder arrangement and a second piston (30) is configured to be displaced inside a cavity (40) defined inside the first piston (10) with the axis of the cavity (40) being coaxial with the axis (A) of the cylinder. A lubricating oil passage (50) defined to pass through the first piston (10), the second piston (30) and the cylinder (20) of the piston cylinder arrangement. The apparatus facilitates reduction in vibrations, slack elimination and automatic lubrication of the chain drive.

A hydraulic tensioning device for a chain drive of an internal combustion engine, having a receptacle and having a tensioning piston which is guided in displaceable fashion in a cylindrical hollow space of the receptacle and which has a piston hollow space, wherein the piston hollow space together with the cylindrical hollow space of the receptacle forms a pressure chamber, and having a pressure relief valve unit arranged in the piston hollow space. The pressure relief valve unit is a preassembled structural unit and comprises a spring, a closing body and a valve seat and also a valve receptacle which surrounds the valve seat in a first subsection, wherein the valve receptacle forms an interference fit with the valve seat, and wherein the valve receptacle or the valve seat in a second subsection form an interference fit with the inner shell surface of the tensioning piston.

One or more radial holes in the body of the hydraulic tensioner are used to control outward hydraulic flow restriction from the hydraulic pressure chamber within the piston. The one or more holes can be arranged in different ways to allow the piston position to alter the outward oil flow of the tensioner.

A chain tensioner is provided which is configured such that the air remaining in a pressure chamber can be discharged to the outside through a helical gap defined between a screw and a threaded hole, and through between circumferentially separate radial ends of a spring washer mounted between the screw and a housing. The chain tensioner includes an air discharge groove or grooves formed in the seat surface of the head of the screw such that an annular space defined between the neck of the screw and the inner diameter surface of the spring washer communicates with the outside through the air discharge groove or grooves. Even if foreign objects clog the space between the separate radial ends so as to hinder air from being discharged through between the separate radial ends, the air remaining in the pressure chamber can be discharged to the outside through the air discharge groove or grooves.

A hydraulic tensioner having a piston sliding around an outside surface of a pin or rod, so that the high pressure chamber for chain control is created by the area between the piston internal diameter and the rod outside diameter. A spring around the outside of the rod presses against the bottom of the piston, biasing the piston outward during low oil pressure conditions. Preferably, the piston is steel and the rod is aluminum, the reverse of prior art designs, which means that as temperature increases, the piston to bore clearance reduces. This can offset the oil viscosity reduction and maintain the same performance over operating temperatures.

A chain tensioner is provided which is configured such that the air remaining in a pressure chamber can be discharged to the outside through a helical gap defined between a screw and a threaded hole, and through between circumferentially separate radial ends of a spring washer mounted between the screw and a housing. The chain tensioner includes an air discharge groove or grooves formed in the seat surface of the head of the screw such that an annular space defined between the neck of the screw and the inner diameter surface of the spring washer communicates with the outside through the air discharge groove or grooves. Even if foreign objects clog the space between the separate radial ends so as to hinder air from being discharged through between the separate radial ends, the air remaining in the pressure chamber can be discharged to the outside through the air discharge groove or grooves.