Patent ID: 6039020
Filing Date: 2000-03-21
Classification: F01M,F02B,F16N

Abstract:
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 through said push rod opening;an oil mist generator drivably connected to said crankshaft, liquid oil in said lubrication oil chamber being agitated by said oil mist generator into an oil mist;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 lubrication oil mist distribution throughout the 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; andoil mist flow passage structure extending from said crankshaft passage to said induction system whereby crankcase gases are scavenged.