Vibration

[SimonD]

Although my Volvo 2002 runs smoothly enough out of gear, I get some vibration between 2000 and 2400 rpm when it's driving the boat. I checked the (badly out) propshaft alignment and that improved matters, but it's not quite right.

I guess it's either a bent propshaft (I'll try to borrow a dial gauge to check that) or could it be the prop. I guess props are balanced at manufacture, but can they become unbalanced and how do I check?

Advice gratefully received.

Simon

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[tony_brighton]

Possibly engine mounts as well?

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[SimonD]

Hadn't thought of that. Does the fact that it seems to smooth out above 2400 rpm make any difference to that diagnosis?

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[Guest]

All sorts .... worn shaft bearing, slight nick on one blade, engine mount sheared, poor coupling alignment ...... these all succumb to age and need resetting eventually.

My Perkins was sweet as a die till I hit cruising revs ..then it shook the house down ... mounts were shot.


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[Guest]

Yes because it can be smoothed out in relation to harmonics ....

<hr width=100% size=1>Nigel ...
So WHAT does the EU really stand for ????/forums/images/icons/cool.gif

 

[catmandoo]

sounds like you are hitting the natural frequency of the system . Have you checked clearances at support points. Does vibration disappear over 2400 rpm?

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[mikesharp]

Had a similar problem with fairly bad vibration at 1500 revs on a boat with an off-set prop. Turned out to be a broken P bracket. Is the boat out of the water? , if so should be easy to check for unusual movement and any good engineering firm should have a flat bed that they can check the shaft for straightness. A visual scan of the prop should indicate balance problems.

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[SimonD]

Thanks - lots to go on. I think I can discount some though. When I bought the boat in June the P bracket looked fine and was secure, the prop looked OK (although I didn't give it a minute examination) and I had a new cutlass bearing fitted.

When I adjusted the alignment in July (boat in the water) the engine mounts looked OK, but again I didn't examine them that closely.

She's now out the water and I'll take a closer look at these items. I guess it could be caused by something not immediately obvious.

Thanks again for the advice folks.

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