Abstract: A turbine type air motor including a rotor and driven spindle having automatic speed regulation. The spindle and rotor have cooperating ports to control the flow of air to the rotor, and the spindle has provision for limited twisting movement within the rotor for moving the ports into and out of register. A biasing spring interposed between the spindle and rotor urges the ports normally out of register when the tool is lightly loaded. An increase in the load imposed upon the spindle causes the spindle to retreat relative to the rotor and against the force of the spring to bring the ports into register, thereby to increase the flow of air so that the torque developed by the rotor increases in step with the torque loading imposed on the spindle to maintain speed. In the preferred embodiment the spindle is of hollow construction and compressed air is fed axially into the hollow for transmission into the rotor through radial ports.