An internal combustion engine includes separated oil drain-back and crankcase ventilation passages. The oil drain-back passages extend from the cylinder head to a position below the top level of oil in the engine's crankcase. The crankcase ventilation passages extend from passages formed in the main bearing bulkheads from positions above the oil level in the crankcase and ultimately through the cylinder head. Oil dams surrounding the uppermost portions of the crankcase ventilation passages prevent oil from running downwardly through the crankcase ventilation passages.
This invention was made with Government support under NREL Subcontract NO. ZCB-4-13032-02 Prime Contract No. DE-AC36-83CH10093 awarded by the Department of Energy. The Government has certain rights in this invention.