A rotationally adjustable support mechanism, which is particularly adapted for mounting on a motor housing, allows a first supported part (e.g., a sensor) to be accurately adjusted angularly relative to a second part (e.g., a shaft mounted code wheel). A specially constructed and uniquely mounted semicircular bushing allows the mechanism (together with the first part supported thereon) to be readily mounted on or removed from the motor housing without requiring the removal of the shaft mounted second part and/or any other associated apparatus.