ORIGINAL: sodbuster 1
Have you tired running the engine without the heavy hub and nut just to rule them out?
You're putting a decent amount of weight out on the very tip of that engine shaft. Anything slightly out that far out on the shaft more than likely is going to magnify itself at higher RPM as your engine seems to be doing.
But I definitely agree with W8Ye.Profile planes inherintly seem to magnify vibration, as most Pro's will tell you just from the foaming fuel tanks on them
It isn't a Higley heavy hub, just the lightweight aluminum spinner one. It's some kind of harmonic vibration thing, it only does it at 5000 rpm + or - a few hundred. And the tank does foam like the first pour after the beer keg is opened. Right in the hover rpm area too, the whole plane shakes and the Monokote really drums. If we had a few more like that we could start an RC band.
Some people are putting metal or carbon fiber engine mounting rails on their profiles helps a little I hear.
I wonder what goes wrong in the manufacturing process that causes a few Saitos to shake badly right out of the box and most to be fine.
I've ordered a set of bearings, if that doesn't fix it I'll have it "put down" maybe do it myself with my 9 mm....