valves stems 7 8 respectively which are biased by means of return springs 9 10 in the valve closing direction the two valve stems 7 8 have their respective end faces bearing against a single thrust member 11 which is shared by both valves 1 2 and which in this embodiment is in the form of a bucket shaped member one salient feature of the invention is that the end faces of the valve stems 7 8 ar engaging the thrust member 11 outside the longitudinal axes 12 13 of the valve stems 7 8 to illustrate this feature lines 14 15 which are extending through the respective points of engagement have been inserted into the drawing the thrust member 11 is mounted in a wall 16 of the internal combustion engine not shown and is adapted for axial displacement and rotary movement about its axis on top of the thrust member 11 there is mounted a camshaft 18 having a cam 19 which engages the upper end face of the thrust member 11 here too the axial center line of the thrust member 11 is offset with respect to the center line denoted by the numeral 20 when the camshaft 18 is turning the cam 19 will urge the thrust member 11 downwardly this downward movement of the thrust member 11 will cause axial displacement of the valve stems 7.