A belt tensioning assembly for use with a power transmission system (10) including a belt (18) extending between a driver pulley (19) and a driven pulley (15) is provided. The tensioning assembly includes an idler (58) engageable with the belt and rotatably attached to a frame (51) pivotally secured to a base for the power transmission system (10) adjacent the driver pulley (19). A biasing assembly is pivotally attached between the frame (51) and the base for the transmission system and includes a biasing mechanism (70) adapted to urge the idler contact with into the belt. As the tension in the belt changes due to changes in the power demand, the idler is automatically urged with varying force against the slack side of the belt by the biasing mechanism to provide near constant tension on the belt as it moves between the pulleys.
