A valve gear mechanism for an internal combustion engine includes a camshaft in a separate cylinder head for controlling the stroke of a gas shuttle valve by means of an interposed rocker arm, which is mounted in the cylinder head of a piston that performs a lifting motion of a hydraulic valve-play compensation element. The aim of the invention is to achieve a play-free surface liaison of mechanical origin between the actuating elements of the gas shuttle valve. To achieve this, the piston of the hydraulic compensation element has a device that acts on an instrument for mechanically actuating a lifting stroke in order to achieve a play-free surface liaison of the contract surfaces of the rocker arm and an additional valve gear element, while the valve-play compensation element is maintained hydraulically without pressure.