A first belt tensioner includes an arm, spring case, coil spring, and arm plate. The arm is adapted to support an idler pulley and has a hook portion. The spring case is disposed in the arm and has a first spring seat. The spring is disposed in the spring case. The arm plate has a second spring seat. The spring is longitudinally compressed between the arm plate and the spring case. The spring is in torsion with the end portions of the spring seated against a corresponding spring seat and with the arm plate rotationally positioned under the hook portion. A method for assembling the first belt tensioner includes using the arm plate to longitudinally compress the spring and rotating the arm plate. A second belt tensioner includes an arm, spring case, coil spring, arm plate, and pivot bushing.