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 crankcase includes a fuel inlet port and an outlet port, and a duct connects the outlet port to an intake passage in the head. 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, the duct, and the air intake passage to the cylinder. Valves and valve actuating mechanisms control the flow of the mixture to the cylinder and the flow of exhaust from the cylinder. The oil in the mixture lubricates the engine parts in the crankcase, the valves and the valve actuating mechanisms. The duct preferably forms a plenum or surge tank containing the mixture under pressure.

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.