Abstract: A camshaft arrangement including a pair of cams (7, 8 ) mounted on the same camshaft (1) with at least one of the cams rotatable relative to the camshaft (17) and with the cams (7, 8) maintained at a given axial spacing on the camshaft (1), a differential mechanism (a, b, c, d) coupling the two cams (7, 8) together for rotation about the camshaft axis with a selected relative angular phase, and phase adjusting means (14, 15) for acting on the differential mechanism (a, b, c, d) to effect a relative rotation of the cams (7, 8) to adjust the selected angular phase of the cams (7, 8) and thereafter to retain the cams in the adjusted position.