A tensioner (10) for an endless loop power transmission member can induce a piston (12) operably engageable with an endless loop power transmission member, and a cylinder (14) guiding include a piston (12) for sliding coaxial movement in a direction of the endless loop power transmission member. The piston (12) and cylinder (14) defining an oil reservoir or pressure chamber (26) for receiving hydraulic fluid. A bearing (28) has bearing balls (30) located in a counter bore (32) coaxil with cylinder bore (34). The counter bore (32) has a steep taper (36) on which the bearing balls (30) ride. As the cylinder (14) moves in an extending direction, the bearing balls (30) move out of the counter bore (32) allowing free extending movement of the cylinder (14). As the cylinder (14) moves in a retracting direction, the bearing balls (30) are driven down into the steep taper (36) preventing the cylinder (14) from retracting.