I can not get my BME-50 clone to run as smooth as I want. It goes out of balance at about 4800 rpm. It is a harmoninc thing that does smooth out a bit at higher RPMs. The crank, hub and prop are all dial indicated within a couple of thousands. I did that on a lathe with the crank/hub assembled. The hub is true to a thousandth, I just made a new hub today, it is straight. The props are Vess and I did balance those down to the gnats's behind. The crank bearings are in good shape. The timing is correct and has no effect on this.

So, I took a Menz prop that was previously drilled for a six hole hub. I added lead to one of the holes, thereby purposly making a heavy side. I ran a marker aginast the hub while running 4800 rpm to find the high side. I installed the prop with the lead opposite the high side of vibration. The vibration got better.

Could the crank have been made put of balance? Would the original chain saw flywheel have been made to dynamicaly balance the whole system? If so should I figure out how much to remove from the hub to pull it into balance using lead weights?

On a happy note, the pitts muffler for the CRRC 40 kit engine fits the BME-50 perfectly.