Multiple-position, operator-carried, four-stroke engine

Abstract

A portable, operator-carried power tool having an implement supported on an operator-carried frame, and a lightweight, four-stroke, internal combustion engine drivably connected to the implement and supported by the frame. The engine has a crankshaft situated in a crankshaft housing and a cylinder block secured to the crankshaft housing, the crankshaft being provided with a crankcase ventilation passage extending between the crankcase and an outlet end in communication with an air/fuel induction passage. A passage establishes communication between the interior of the crankcase and the valve chamber through a cam and cam gear region of the cylinder block. An oil mist generator is connected drivably to the crankshaft for agitating liquid oil in the crankcase to establish a lubricating oil mist. The crankcase, the cam region and the valve chamber form a closed oil mist containment whereby lubricating oil mist is distributed throughout the engine during operation regardless of angular orientation of the engine. The crankshaft ventilation passage establishes lean crankcase gas distribution to the engine air/fuel intake. The crankcase is designed to avoid flow of liquid oil through the crankshaft passage when the engine is not running.