Vibration

[flyingwaldo]

I recently had my prop balanced by Craig and then the "drivetrain" by Jeremy.  The prop and spinning parts are excellent without any adjustments but I have a big spike that indicates something touching.  Can't find anything....
Can and do engine mounts 'go bad' after time?  The airframe has had an engine mounted for 13 years now.  I found the bolts at the dynafocal loose recently and tightened them up without removing the weight and was told that was incorrect.  So I did it again and had the weight supported by a hoist while tightening to torque.  Small improvement in vibration but not all.  Any suggestions would be appreciated.
Thank you.

[Radioflyer]

Of course the engine rubber mounts can go bad, but usually after some aging. 13 years can be more than enough aging. Does the rubber have cracks? Are the bolts much closer to one side of the ring or generally in the center of the ring (in other words does the rubber show a set or sag)? The rubber is normally pretty hard, but when I replaced mine, they were like rocks...not capable of attenuating any vibration.
I would consider the possibility of a cracked engine mount. Carefully look over your aluminum extrusions and your motormount welds, especially around the dynafocal rings.
Just a thought.