through the radial gap 53 and other gaps which incidentally occur in fabrication for instance on the circumference of the cam 41 the sidewalls 52 protrude radially inward up into the area of the center disk 6 so that here too an axial seal may be provided for example a maze seal fig2 a in a diagrammatic cylinder section shows the peripheral area between the cam 41 and the area between the sidewalls 52 of the capsule 50 on the cam 41 there are provided on both sides friction elements 60 which axially run in openings 42 in the cam 41 by way of projections 64 the two friction elements 60 are axially expanded outwardly by means of an expansion spring 61 the bolt 62 is in the present embodiment fastened to the one friction element 60 and features on the other end a stop 63 which adjusts the two friction elements 60 to an axial dimension a this axial dimension a in the rotational position where the cam 41 has not moved yet between the sidewalls 52 of the capsule 50 is greater than the clearance b between the sidewalls 52 fig2 b shows the rotated condition of the.