The present invention comprises a hydraulic tensioner for applying tension to a chain without external fluid pressure supply. The hydraulic tensioner includes a piston assembly comprising a piston with a hollow interior and a piston bore surrounding the piston. An end of the piston assembly is submerged in fluid. An inlet check valve, which controls an entry of fluid into the piston, is located below the fluid level. An outlet check valve, located at an opposite end of the piston assembly from the inlet check valve, controls an exit of fluid from the piston. A non-return mechanism is coupled to the piston such that the piston extends but does not retract more than an included backlash amount. Utilizing the motion allowed within this backlash amount, the tensioner acts as a self-priming pump.