Abstract: A variable-timing valve actuating mechanism for an internal combustion engine having an axially movable cam shaft, movable by a governor device to a position proportional to engine rpm. A set of dual cams is provided for operating intake and exhaust valves with a uniform profile lobe effective only over an idle to medium rpm range and a non-uniform profile lobe effective only over a medium to maximum rpm range. A timing gear drives the cam shaft and utilizes a spiral spine drive to also advance and retard the cam shaft rotation proportional to the cam shaft axial position. The variable advance/retard action and the non-uniform cam lobe are selected to optimize valve overlap, valve opening angle, and valve timing as a function of rpm.