Patent ID: 7077089

Claim:
An internal combustion engine, comprising: a crankcase having walls which define an interior volume for containing oil and which define a cylinder; a piston moveably positioned within the cylinder of the crankcase; a cylinder head having a proximal end fastened to the crankcase, the cylinder head extending laterally outward from the crankcase and terminating at a distal end; a rocker arm cover, fastened to the distal end of the cylinder head, the rocker arm cover defining a cavity therein which forms a valve box; a drainback passage interconnecting the interior volume of the crankcase and the valve box to enable the flow of fluid from the valve box to the interior volume of the crankcase; and a check valve, disposed within the drainback passage, for allowing the flow of fluid from the valve box to the interior volume of the crankcase and preventing the flow of fluid from the interior volume of the crankcase to the valve box, wherein the check valve includes a check ball seating against a bore defining at least a portion of the drainback passage at the proximal end of the cylinder head to prevent the flow of fluid from the interior volume of the crankcase to the valve box when there is high pressure present within the crankcase or when the engine is operated at an elevated angle; whereim the cylinder head has a first bore formed therethrough extending from the distal end to the proximal end of the cylinder head; the cylinder has a cylinder wall, integrally formed in the one wall of the crankcase and having an interior surface that communicates with the interior volume of the crankcase and an exterior surface that engages the proximal end of the cylinder head; and the cylinder wall has a second bore formed therethrough extending from the interior surface to the exterior surface, where it aligns with and couples to the cylinder head bore, wherein the first bore and the second bore together define the drainback passage, and said check ball is disposed in a cavity formed at one end of said second bore and seats against said second bore to prevent the flow of fluid from the interior volume of the crankcase to the valve box when there is high pressure present within the crankcase or when the engine is operated at an elevated angle.