MULTIPLE-POSITION, OPERATOR-CARRIED, FOUR-STROKE ENGINE

摘要

A portable, operator-carrier power tool having an implement supported on an operator-carrier frame, and a lightweight, four-stroke, internal combustion engine (16) drivably connected to the implement and supported by the frame (12). The engine (16) has a crankshaft (28) situated in a crankshaft housing (24) and a cylinder block (74) secured to the crankshaft housing (24), the crankshaft (28) 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 (118) and cam gear region of the cylinder block (74). An oil mist generator (141) is connected drivably to the crankshaft (28) 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 (16) 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.