[Learjetter]

Searched, found nothing on point. Flew last week and with RPM about 2300, reduced throttles to 12-15” in the pattern. Felt an unusual vibration and subsequent flights with another pilot makes us think it was the rear engine vibrating more than I remember. We removed and cleaned and reinstalled all plugs, especially since we could hold the plugs cyl #2 on rear engine and the rest were too hot to hold. Maybe a little less vibration at idle on subsequent engine run. Rear engine has about 110 hrs since MOH at Mena.

So, how much tail boom and vertical stab vibration is “normal”? Had A&P listen to the engine runs and he commented on the amount of tail vibration he saw. Also, the rear engine can be moved 1/2”-1” in every direction by pushing up or down on the spinner. Is that normal for 337s?

What’s different since previous less shaky flights? Overhauled and statically balanced MT props.

I’m beginning to think the R mag doesn’t work well at idle. Both engines seem to run smooth and throaty for takeoff and cruise. But rear gets rougher and shakier at lower RPM on R mag only (about 150 rpm drop on mag check, about 100 rpm drop on L mag check)

I’d really appreciate any thoughts on next steps to try. I do not have a reliable engine monitor yet...but plannng to install EDM-960 or MVP-50s this spring.