Marty----Engine parts should not "unbalance" themselves, once balanced.
Changes can occur in accessories, such as the alternator, and produce a
buzz. Also in the drive train, such as U-joints. It depends on whether
you were on the road when you felt these vibrations.
I believe my engine was balanced with the damper attached, as well as
the clutch package, at the time. (At least they asked me to bring these
items. It's possible that they checked these separately)
This engine also goes thru some harmonics at 3000-3500, if the engine
isn't loaded, such as a simple revving. I keep these exercises to a
minimum.
Dick
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