That's really cool!! It could be that the reason we hear, (and experience) "grenading" of the Ryobi when run over 7500 rpms or so is because in our airplanes when they do so it is for a much longer period of time than with boats. I have however, heard of many coming apart when run too high of an rpm. I have often thought about machining up an aluminum rod for one just for the hell of it. I think the rod is the weak link; the stamped steel crank assembly/counterweight should be no problem.

Anyway, nice project!

AV8TOR