Valve cam mechanism for four-cycle engine

Abstract

A valve cam mechanism for a four-cycle engine includes an improved construction. The engine includes at least one camshaft having cam lobes to actuate intake and exhaust valves. A decompression actuator is affixed to the camshaft for pivotal movement. A holder section of the actuator is arranged to hold the intake or exhaust valve in an open position when the actuator exists in an initial position. A weight section is disposed opposite to the holder section relative to the pivot axis to place the holder section in the initial position. The actuator pivots when the weight section moves by centrifugal force to release the holder section from the initial position. The camshaft further has a projection extending radially and defining a first surface on which the stopper section abuts to inhibit the actuator from pivoting beyond a preset range. The cam lobe includes a base circle portion and a nose portion protruding from the base circle of the cam lobe. The nose portion is cured to be harder than the base circle portion. The base circle portion defines a second surface projecting toward the actuator. The holder section abuts on the second surface when the actuator lies in the initial position. The side surface is finished by a machining process.