Abstract: A belt tensioner suitable for use with an automotive serpentine belt system comprising a fixed structure adapted to be mounted on an automotive engine, a pivoted structure mounted on the fixed structure for pivotal movement about a pivotal axis between an installation position and a maximum extension position, a torsional metal spring operatively connected between the fixed structure and the pivoted structure for resiliently biasing the pivoted structure toward the maximum extension position, and a belt engaging pulley rotatably mounted on the pivoted structure for rotational movement about a rotational axis spaced from the pivotal axis. The torsional metal spring is in the form of a helical coil having opposite end portions connection with the fixed and pivoted structures respectively with a major portion of the helical coil formation between the opposite end portions being disposed in spaced relation with the fixed and pivoted structures.