Vibration at low RPM's

[randyb]

Hello Fellow Albineers,
I have a '95 28TE with a Cummins 6BTA 250HP. The purpose of this post is to request some ideas to solve a low RMP jitter, vibration. The boat rattles pretty hard when placed in-gear and under 900 RPM. I "maxed" the idle up to 850 and the vibration is reduced yet not eliminated. Prop is clean and not especially dinged. The mechanics point me to my running gear and running gear guys tell me it's engine mounts. Any ideas on identifying, isolating the problem? Ideas and opinions welcome.

Make it a great day!
-randyb

[Russell]

I had the same problem with my previous boat with the same engine. At idle speed everything in the pilot house would vibrate and you could hardly hear one another talk. Replacing the engine mounts made a tremendous difference in sound and vibration. Mine was a 97 model and I replaced the mounts in 2008.

[Yearwood]

Have a 28 TE 2001 w/Yanmar and have had same problem. About 5 years ago, one "expert" mechanic said it was engine mounts, but had enough sense to check further. Told local dealer of the problem and possible engine mount problem. Took boat in and within half an hour of the mechanic getting aboard he told me the engine mounts looked just like engine mounts of that age should look, nothing was wrong with them, vibration was an issue with the Yanmar having the same number of hours. He raised the idle and it was fine, until this year and I may raise the idle again.

[whwells]

Yearwood: Had same problem with Cummins 8.3 with one engine shaking at idle. We did same raise the idle speed to match other side and all is fine.
Have not yet determined how one engine slowed down a bit.
whwells "Howard"