Patent ID: 8490596

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 piston mounted for reciprocation in the cylinder; a side cover attached to the cylinder block at a face parallel to an axis of said cylinder and perpendicular to a crankshaft axis defining a crankcase and an oil reservoir with said cylinder block; a 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 therefrom within said valve chamber and engaging said rocker arm; a vertical crankshaft or a horizontal crankshaft pivotably mounted by a ball bearing or a plain bearing in the cylinder block and a ball bearing or a plain bearing in said a side cover, said crankshaft including a crank portion and at least one counterweight web, a connecting rod having articulated connections at one end thereof to said piston and at an opposite end thereof to said crank portion, thereby forming a piston-connecting rod crankshaft assembly; at least one cam rotatably mounted on a camshaft which is pivotably supported by said cylinder block and said side cover, said camshaft is connected to a cam gear driven by a crank gear on said crankshaft 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 at least one cam; and a trochoid oil pump connected drivably to said camshaft and placed at a wall of said side cover, wherein an inner and outer rotor of said oil pump are placed in said side cover and inhales lubrication oil from said oil reservoir through an inlet passage and splashes the oil into the cylinder and the valve chamber to lubricate the engine parts inside the cylinder and the valve chamber, wherein an inlet hole of oil into said inlet passage is dipped in lubrication oil.