I have built a plane that had a sheeted stringer fuse, very long fuse. The plane didn't vibrate at all anyplace except the tail feathers, nothing to do about it, just the nature of the beast. Have you mounted your engine on a stand or other air frame? Was the engine ever in a crash? Maybe a slight bend in the rod?? Without seeing the plane it's hard to come up with any answer, all we can do is think of problems it could be. MDS engines were/are not the cream of the crop. Horizon gave up selling them for a number of reasons. That's why I have a few under the bench. I won't get into the problems I had with them but I don't even give them a thought when I am looking for an engine to use.