In an aspect, an isolation device is provided for a belt and a component shaft in an engine. The device includes a hub, a pulley, an isolation spring and a damping member that is fixed rotationally relative to the hub and is engageable frictionally with the pulley. Torque transmission through the spring below a selected non-zero torque, irrespective of hub load on the pulley, drives a change in radius of the helical coils of the spring that is sufficiently small that the spring avoids pressing the damping member against the pulley. Torque transmission through the spring above the selected non-zero torque, irrespective of hub load on the pulley, drives a change in radius of the helical coils that is sufficiently large that the isolation spring applies a radial force to press the damping member against the pulley so as to generate frictional damping.