The Development of a Durable, Cost Effective, Overhead Valve Train for Application to Small, 4-Cycle Engines

This paper outlines the specifics of valve train design and construction for a small 26.2 cc, OHV, 4-cycle engine recently developed by the Ryobi Group of Companies for hand held power equipment applications. The first generation of this engine was designed to compete with existing 2-cycle technology for nylon string trimmers. As such, the valve train operates reliably at engine speeds in excess of 8,500 r.p.m. Design methodologies to minimize forces that develop during high speed operation will be reviewed. The lifter mechanism design facilitates parametric tuning of engine performance by simple variations in the geometry. A unique combination of nickel free stainless steel valve and polymeric valve spring retainer materials were used to avoid wear in the valve stem and limit valve float in a single spring design.