Patent ID: 7287508

Claim:
A single-cylinder, four-stroke cycle, spark ignition internal combustion engine for mounting on a power tool comprising: a cylinder block having a cylinder, a cylinder head, a piston mounted for reciprocation in said cylinder, said cylinder head defining an air-fuel combustion chamber; an air-fuel mixture intake port and an exhaust gas port in said cylinder head; a valve cover on said cylinder head defining a valve chamber; an intake valve and an exhaust valve mounted in said intake and exhaust port, respectively, for reciprocation between port-open and port-closed positions; a valve-actuating valve train, said valve train including at least one rocker arm and at least one valve train push rod assembly extending at one end thereof within said valve chamber and engaging said rocker arm; a crankshaft rotatably mounted in a crankcase, said crankshaft includes a crank portion and at least one counterweight web; a connecting rod having articulated connections at one end thereof to said piston and at the opposite end thereof to said crank portion thereby forming a piston-connecting rod crankshaft assembly; a cam rotatably mounted in a cam housing, said cam being drivably connected to said crankshaft having a cam gear, said cam driven at one-half crankshaft speed, the opposite end of said push rod assembly being drivably connected to said cam whereby said push rod assembly is actuated with a reciprocating motion upon rotation of said cam; a lubrication oil reservoir formed below the crankcase; an oil pump connected drivably to said cam gear-cam assembly, said pump inhales lubrication oil from said oil reservoir and splashes the oil into the cylinder and the valve chamber to lubricate the engine parts inside the cylinder and the valve chamber; a first wall at least partially surrounding around said web with a slight distance therefrom; and a second wall at least partially surrounding around said first wall with a distance gradually increasing toward the downstream of the direction of the rotation of said web; wherein said web splashes the oil to lubricate the internal engine parts and, after lubricating the internal engine parts, the oil is forced to return into said oil reservoir guided by said second wall as the web rotates due to the viscosity of the oil between said web and the first wall.