Madmanmike,

After thinking about your description of the vibration problem I suspect you have either worn out the bearing in the front of the engine or possibly bent the crankshaft a little bit (can't imagine how that could happen ). The key, I think, is that you don't see the problem when running the Top Flite wood props, and you do see the problem when running the plastic props. My thinking goes something like this. The wooden props are extremely rigid as compared to the plastic props. Try flexing the tips of a wooden prop and you'll see what I mean. With a plastic prop you can flex the tips of the props, not much I grant you, but some. So, if the prop shaft is running out of round this could cause the tips to flex while the engine is running, and the problem should be more noticeable at lower RPM's when the tips will have time to move. As you increase the RPM's you would reach a point where the blades are getting around faster the the tips can flex and the vibration will stop. I have no idea how you might determine if the prop shaft is bent or not, or if you have a worn bearing for that matter. Maybe someone with machinist training will offer some information about that.

Bill Sindel