<div class="htmlview paragraph"> </div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Ryobi Outdoor Products (ROP) in Arizona, one of the subsidiaries of Ryobi Group of companies, developed 26.2cc OHV engine for string trimmers. (<span class="xref">2</span>) The outline of the valve train of this engine was presented at the SAE conference at Indianapolis 1996.(<span class="xref">3</span>) This paper describes methodologies and theoretical considerations by which such a unique valve train was developed. The theoretical consideration includes how optimize the valve train design to minimize the moving mass as a total system. Methodology for optimizing the design of each component of valve train is also presented. A review of how the theoretical optimization was translated into the final production engine design is given. The experimental effort to optimize cylinder head design to make the overall optimized design theory reality is described.</div> <div class="htmlview paragraph"> </div>