I'm feel so much better. I kinda figured but, wanted some confirmation. I did not run my engine at the resonant freq. very long. Maybe 5 seconds three or four times. I though if it was unbalanced or bent, it would do this at any RMP not just one spot. Plus, the engine is huge by my standards and the 16" prop is no small thing either so, I'm sure I would have noticed other symptoms if something were damaged.

I built the test stand for 40 size engines, I thought since I was mounting to 1/2" ply I would be ok. I was wrong. I'll be sure to brace the mounting board before I run it again. I think I'll also be securing this to something more sturdy than the metal stand too.

Thanks again,
-Rocko

RCU Rocks!