Self-contained hydraulic variable valve timing systems for use with internal combustion engines include an especially adapted valve cover which integrally includes a hydraulic lifter, a solenoid valve, and fluid passageways fluid connecting the lifter and solenoid valve. In one embodiment, separated cam follower and valve actuating pistons form respective fluid-connected chambers in a case integral with the valve cover, these chambers also being in fluid communication with the solenoid valve via a control passageway. Cam-following motion of the cam follower piston may be hydraulically transferred to the valve actuating piston when the selenoid valve is operated so as to open one valve of the engine, or to simultaneously open a number of valves. An overhead cam may be mounted within the valve cover with the hydraulic lifters disposed between the cam and the valves of the engine. The valve cover will therefore define the fluid passageways so as to operatively interconnect the solenoid valve in the cover to the hydraulic valve lifters.