Abstract: A belt tensioning device is provided for a pulley drive mechanism including a motor with a drive shaft, a drive pulley mounted on a drive shaft, an idler pulley rotatably mounted in a pulley support, and a drive belt trained around the pulleys. The belt tensioning device includes a scissor jack connected between the motor and the idler pulley support. The jack is extendible so as to increase the spacing between the pulleys and thereby increase the belt tension, and retractable so as to decrease the spacing between the pulleys and thereby decrease the belt tension. The extension and retraction of the scissor arms of the jack is controlled by a draw bolt, or alternatively, by a spring which automatically provides tension on the belt. In the method of adjusting the belt tension, the jack is installed between the drive pulley and the idler pulley, and the jack is then actuated so as to adjust the spacing between the pulleys and thereby adjust the tension of the drive belt.