The subject of engine over-speeding was discussed in the Franklin Service News, dated 2/1/54, issue No. FSN 39. Most of you will probably never experience over speeding (the most common complaint I here often is that the engine won’t reach rated RPM). But incase you do experience the situation the following is from Franklin:
The service letter also discusses other engines such as the 6V4-178-B32 and the 6V4-200-C32. These are helicopter engines and have many parts in common with the 165 horsepower engine. They run at much higher RPMs and therefore have strong parts. Particularly, the rods and exhaust valves will fit the 165 and would be better than stock parts. At least two members have used 178 parts to rebuild their 165.