Over the last few months, my mechanic and I have been fighting an engine vibration problem that started after I had my airplane painted. We finally tried several different prop positions to see what impact it might have on the vibration problem. Apparently, my fixed-pitch propeller can be installed in any orientation on the mounting bushings of my O-320-D2A (Lycoming Service Instruction #1098G notwithstanding). Last week, we moved it one more time. I am quite sure it is now back in the position it was in when I bought the plane. There still seems to be a bit of "harshness," real or imagined in the engine, but the vibration is significantly reduced. This is what puzzles me. Can prop position make such a large difference? Since being moved, I have gotten two differing views from two mechanics as to whether the prop is currently in the correct position on the flange or not. Fact is, this is how all the prop re-orientation started because my mechanic was convinced the propeller wasn't installed correctly at the paint shop.
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