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

[Joe Jablonowski]

 My boatyard replaced the motor mounts on my Perkins Perama 30 also, using mounts I'd purchased from England.Trouble is, they re-used the lag bolts from the previous mounts, and one sheared off.After I discovered the bolt head in the bottom of the engine compartment, drilled out the stud and replaced it, a lot of the vibration ended.- Joe Jablonowski  s/v Assignment 1994 C320
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    On Friday, December 11, 2020, 11:34:26 AM EST, Age Of Aquariums <dan at ageofaquariums.biz> wrote:  
 
 my perkins does the same thing , i don’t go below 1100

> On Dec 11, 2020, at 8:17 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