Vibration dilemma

[lgsailor19]

On my Catalina 30, with Universal 25, we get a vibration at various rpm''s. Sounds like something loose rattling in the locker, but we cannot locate anything. We replaced the prop, the cutlass bearing, checked engine alignment, made sure the zinc was on fast. The vibration is more apparent at certain rpm''s , but seems to dissapear at others. No rattle with the transmission in neutral at any rpm. Any ideas??

[GordMay]

No vibration in neutral suggests drive train.
You seem to have checked it out pretty thoroughly, but didn''t mention the shaft to transmission coupling, strut, nor shaft straightness.
Sounds like a "puzzle", all right.
Gord

[DuaneIsing]

lgsailor19,

If you have one of those dripless shaft seals, I know they can vibrate under certain conditions.

If you have one and wish to check it, you can VERY carefully observe it while the transmission is engaged (nothing dangling near roating machinery). In the case I observed, carefully applying pressure to the rubber bellows changed the face seal contact ever so slightly and stopped the vibration (which was surprisingly loud).

To be frank, I don''t know what the long-term solution is in that case, but at least you would know.

If you don''t have a dripless shaft seal, then I take my cue from Saturday Night Live''s Roseanne Rosanadana, "Never Mind!"

Good luck.

[andiamod11]

You might want to check the shaft strut to make sure it has not loosened up. Other problems could be a bent shaft or insufficient propeller tip clearance with the hull.

[Yodagwb]

Many boats with diesels have RPMs which the boat is not happy with. I have a range in my Cat350 which make all kinds of things rattle and weird sounds, harmonic resonance. Once you get away from that RPM range things quite down. Could this be what you are dealing with?

[lgsailor19]

The vibration is too loud to be harmonic resonance. My yard mechanic tells me it is a livable situation, that it is no worse than most boats. The vibration has been with me only the last 2 seasons. Prior to last season, no vibrations. Any other ideas? Help!

[garygroves]

You might check your engine mounts to see if one may have a break or worn rubber. While you say you don''t have any vibrations when xmsn is not engaged, typically a broken engine mount would show up here as well. However, the break may be small, such that it needs the additional torque of the spinning shaft to start the vibration sequence. Just a thought to go along with the rest.

[lgsailor19]

How can the driveshaft straightness be checked, short of hauling out and removing the shaft itself?

[capnjim02]

I think there may possibly one other culprit. Its possible that your injectors or possibly one of them may be fouled. under load it may not be correct and causing the engine to miss under load. happened to my friends volvo. one injector was not spraying correct pattern. had it rebuilt and vibration went away.

[lgsailor19]

It isn''t engine related. I think my best leads are; slightly loose strut or a bent prop shaft.