Abstract: A drive mechanism for a rotary drum having a toothed ring which is disposed on the outer periphery thereof with a clearance in relation to the drum and which meshes with a drive pinion, the toothed ring is secured to a cylindrical support arranged concentrically to and with a clearance from the drum, and mutually spaced circumferential portions of the cylindrical support are respectively secured to the drum and to the toothed ring, the support being elastically flexible whereby the toothed ring is able to move radially of the drum with flexure of the support. The toothed ring is held in mesh with the drive pinion by guide and support elements which are disposed at the same radial distance from the drive pinion axis but which are angularly spaced about the axis and bear on an inner peripheral surface of the toothed ring.