Importance

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Abstract

A four-stroke engine comprising an engine frame including a block and a head, the block forming at least one cylinder, and a crankcase. A piston is mounted for reciprocation in the cylinder, and a crank and connecting rod are mounted in the crankcase and connected to the piston. The head supports an intake valve, an exhaust valve, and a valve actuating mechanism, and a valve cover forms an enclosure with the head that encloses the valves and mechanism. The crankcase includes a fuel inlet port and an outlet port, and a duct connects the outlet port to the enclosure in the valve cover. The inlet port is connected to a supply of a combustible mixture comprising fuel, lubricating oil and air. During engine operation, the mixture flows through the crankcase from the fuel inlet port to the outlet port, the piston functioning as a pump to move the mixture. The oil in the mixture lubricates the engine parts in the crankcase. From the outlet port, the mixture flows through the duct to the valve cover and to the intake valve. The enclosure formed by the valve cover contains an oil mist around the valves and the valve actuating mechanism. Valves may be provided at the fuel inlet and outlet ports of the crankcase to achieve crankcase compression of the mixture, and the duct may form a plenum or surge tank containing the mixture under pressure. The duct is preferably separate from the block portion.

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First Claim