Abstract: Crankcase ventilation systems for internal combustion engines generally utilize external lines which increase the complexity of the engine while decreasing the engine's flexibility. Additionally, systems which utilize internal methods for ventilating the blow-by gas leaking past the piston rings generally do not properly ventilate the crankcase. The present invention overcomes these problems by providing crankcase ventilation system which utilizes a simplified design for an internal combustion engine with hydraulically actuated valves. A passage is disposed within the engine for fluid communication between a crankcase and a combustion chamber. A valve means is disposed within the passage for controlling the communication therebetween.