Vibration

Don, how is it going ? Find your problem yet ?

Don, positioning you prop correctly is a must. Dynamic balancing of the prop spinner and engine at run-up is absolutely worth doing too!
I’m assuming you’ve checked the prop for balance and tracking,…?
See recent reply on engine mount replacement.
Cheers,

My Alon C90 mounts are the standard plastic plugs at each end with a rubber hose over each attachment bolt. Log books say engine mounts were changed out 10 years ago, but the plane sat in hangar for those 10 years.
Your post has motivated me to change the mounts out again, in the hopes of seeing positive results, Thanks,

If your engine uses the Lord mounts, suggest you check these very, very carefully. I bought a 415C that had the 0-200 conversion with the Lord mounts. Previous A&P/IA owner, and a friend, said he had tried to cure a severe vibration, including, IIRC, he replaced the prop with an OH that he had sent to well known prop shop. Plane was out of annual since he had relocated to west coast. I got a ferry permit and in flying it home over the mountain, the vibration was so severe, I called approach and notified them. Long story short, checked mount rubbers and didn't like what I saw. Replaced them and problem went away!!!

My ‘66 Alon has a pronounced vibration between 1800 & 2450 RPM. I’ve had the prop checked, changed the plugs, tested the ignition wires, dynamically balanced the prop to 0.02, but the vibration now slightly dampened continues,… it seems a lot of Alon owners have this problem. Any recommendations would be appreciated.

First, make sure the prop is indexed correctly. From the front, it should be at 11 and 5 o'clock. If that is correct, I would suggest turning the prop 180 degrees. From there it gets more complex.