1967 Alon A-2 with C90 History: I noticed what seemed to be excessive engine vibration between 1500 and 2200 RPM. Propeller tracking checked during the plane's annual and was found to be true. Following the advice of previous Ercoupe Tech e-mail, my AP and I replaced the rubber motor mounts and I had another shop conduct a dynamic prop balance. The old rubber motor mounts were in good shape and the prop did not need balancing (i.e. it was well within tolerance according to the AP who performed the work). I printed out and followed the instructions previously offered on Ercoupe Tech for replacing the motor mounts (my AP had experience replacing motor mounts on other aircraft with Continental engines but not in Ercoupes/Aircoupes). We could NOT tighten the mounting bolts to the prescribed 60 inch pounds (we had metal to metal contact between the engine and the mount). At 45 inch pounds there was very little clearance so we settled on 40 inch pounds.
Current situation: After almost 15 hours of flying time, the engine vibration is worse than when I started. Should we try tightening the mounting bolts or loosening them? Any other suggestions? Cruising at 2250 RPM is smooth but I need to fly slower at times, especially in the pattern. Thanks for your help! David N95CV
