Patent ID: 6945215

Claim:
An operator-carried, lightweight power tool comprising a frame with an implement mounted thereon, a four-stroke internal combustion engine with a crankshaft drivably connected to said implement, said engine being supported by said frame; said engine comprising a crankcase with a lubrication oil chamber, a cylinder block secured to said crankcase and having a cylinder bore and a cam chamber; a cylinder head secured to said cylinder block; overhead intake and exhaust valve ports in said cylinder head; a valve cover defining a valve chamber, said valve chamber enclosing intake and exhaust valves which register with said intake and exhaust valve ports; a cam and cam drive mechanism in said cam chamber, said cam drive mechanism including valve operating push rods; a rocker arm assembly in said valve chamber drivably connecting said push rods and said intake and exhaust valves; at least one push rod opening and at least one of said push rods extending through said push rod opening; said crankcase lubrication oil chamber being in communication with said valve chamber; an open passageway between said lubrication oil chamber and said cam chamber whereby said lubrication oil chamber, said cam chamber and said valve chamber define a closed oil mist containment permitting alubrication oil mist distribution throughout said engine; a crankshaft passage formed in said crankshaft including a crankcase gas flow entrance portion extending in a radially outward direction from said crankshaft; said engine having an air/fuel induction system communicating with said intake valve port; and an oil mist flow passage extending from said crankshaft passage to said induction system whereby crankcase gases are scavenged.