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

[Chris Burti]

Proper engine alignment calls for the coupler faces to be gapped at 90 deg
intervals to confirm that the shaft coupler faces are square to the shafts.
If the gap is not the same at all four intervals, you can never align the
engine and will end up with a vibration at some speed. In my experience
this isn't typically done by yards unless you specify it in your work
order.. Once done, you shouldn't have to redo it unless you remove the
coupler from the shaft.

Fair Winds,
Chris Burti
Commitment #867
Farmville, NC

On Fri, Dec 11, 2020 at 11:17 AM Paul Borghese <packetpaul at gmail.com> wrote:

> 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
>