I purchased a used Moki 1.35. I finally got it running on the test stand....tank location was bad. I wasn't getting enough fuel. So with that fixed, this engine really has some power. I did notice one thing. My prop nut also serves as the spinner mount. It's about 1.5" long. At a certain throttle setting bellow mid but above idle, it has the appearance of a bend shaft spinning. In fact it apears as the whole front of the motor (everything that spins) does this all the way back to the block. I reamed a straight hole and balanced the prop as best I can tell. It's ok from idle up to that point and ok above that point all the way to WOT. When I held tight onto my test stand putting weight on it, the "resonating" seemed to get better. My guess is, my motor/test mount is hitting the resonant frequency at that point. Will my test stand damage the engine? Will it do this on a plane? The test stand is clamped to a cast iron fish tank stand. I had lead weights holding the stand down.


The picture shows the engine mounted right side up. While running it I actually clamped the wood portion of the stand sideways so the pitts muffler was on the bottom...engine sideways.

My main concern is that the engine is ok, and that my test stand did not or will not cause damage.

Thanks,
Rocko

The engine is OK. You just reach a resonant frequency. You need some side braces on your vertical mounting board.

That's a pretty flimsey looking test stand.

I agree with w8ye put some side gussets on your stand, I think you will see a tremendous difference in things.

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!

Good deal. This huge engine scares me. I need to get more comfortable with it. Another guy mounted his 1.35 it to a Goldberg Ultimate, I intend to do the same. I'm a bit concerned thought that it's too much engine for that plane, although, it worked for him.