Albert, I have heard from most 'Coupe owners that their planes have more vibration at certain RPMs (for mine, it's around 1700-2000). One thing that an A&P found that took out some extra vibration that had developed was that he discovered the big exhaust pipe (sorry if I'm not using the right term) that goes down through the bottom of the cowling was touching the edge of the cowling hole and so banging against it in operation. When its position was readjusted, and the hole also enlarged a bit, that extra vibration stopped.
Linda N3437H (Sky Sprite) 415-C L.A. Here's his problem with vibration --------------------------------- The only negative impression I have so far is the moderate vibration from 2000 RPM on up to 2500 RPM. My AP/AI changed the prop position to 3 locations and found the best location which helped a little. He also did a dynamic balancing that helped a little more but not much. He said the vibration may show a slight improvement when the engine is broken-in. I hope so. It reminded me of the old C-119's. I did not like the vibration then and do not now. Thank you all again!! Albert Flora N94748 (HYR)
