Valve operating mechanism with roller rocker arm, 4-cycle engine, and motorcycle having 4-cycle engine mounted thereon

摘要

A valve gear includes a camshaft having valve gear cams, first and second rocker shafts, a first rocker arm supported on the first rocker shaft, and a second rocker arm supported on the second rocker shaft: The valve gear cams, respectively, include a cam nose projecting from a base circle, and the first rocker shaft supporting the first rocker arm is positioned forwardly of a center line, which passes through a center of the camshaft to extend axially of a cylinder, in a direction of rotation of the camshaft:. The first rocker shaft is shifted closer to the camshaft than a center of rotation of a roller bearing is, when the roller bearing won the first rocker arm contacts with the base circle of the valve gear cam: