Abstract: A drive mechanism including a toothed pulley and a device for retaining mesh between the teeth of the pulley and the teeth of a belt after assembly thereto. The retaining device includes a retaining member positioned adjacent a toothed section of the pulley defining a space therebetween enabling the belt to fit between the retaining member and the toothed section of the pulley when the teeth are in mesh, the space between an apex or crown of a pulley tooth and the surface of the retaining member opposite thereto being smaller than the maximum thickness of the toothed belt thereby ensuring a mesh between the teeth of the belt and pulley to provide a synchronized drive therebetween.