[C320-list] Severe vibration at 1000 RPMs after engine mount replacement

[Paul Borghese]

A boatyard replaced the engine mounts in my Cat 320 Perkins M30 engine. The
engine is noticeably smoother at all RPMs except one, 1000 RPMs.  At
exactly 1000 RPMs the harmonic vibration causes the engine to shake
violently.

The vibration occurs every time on every transmission setting ( neutral,
forward, reverse).

Any ideas as to the issue?  I have an uneducated theory. The yard used
off-brand engine mounts that were not tuned to the engine causing the
severe vibration.  Or maybe the bolts are not torqued to the correct
specification.

Thoughts?


Paul