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Engine vibration problem


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Hi there

 

We have an isuzu 38hp on our recently purchased NB. The survey threw up both excessive engine vibration on tickover (recommendation adjust running speed) and also excessive play between prop shaft and stern tube (recommendation replace stern tube). I only have a basic knowledge of engines but I have successfully adjusted the tickover speed. However it only solves the problem in the short term - the engine ticks over too fast IMO and vibration still returns after a while, and is causing lots of other problems (exhaust damage, short circuits, sheared mounting plates...).

 

So, I really need to stop this vibration before I fix any other problems as it is the root cause of everything. We are not planning on getting her in dry dock until next year so i'm guessing attention to the stern tube would have to wait until then.

 

My questions are,

 

Could the vibration be related to the stern tube issue? (Bearing in mind that vibration will still occur out of gear with appropriate revs)

Would replacing the engine mounts possibly help or is that a waste of time/money without replacing stern tube also?

Is it a case of do what you can when you can and slowly eliminate the possibilities?

 

Thanks for looking

 

 

 

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Don't mean to insult your intelligence, but are the engine mount nuts/bolts all tight? My engine did similar once, and the mounts had worked loose.

It might help if you can give more details of the installation (which flexible coupling etc) or better still a photo.

 

Another possibility is the engine may not be mounted correctly on the mounts, which can cause "rocking" diagonally from corner to corner.

Edited by Guest
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Ditto catweasel, I found a loose nut on just one of the mounts on my 1.8 bmc responsible for

significant vibration when I first got my boat, it was also one of the ones underneath so not

immediately visible.

 

springy

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Ditto catweasel, I found a loose nut on just one of the mounts on my 1.8 bmc responsible for

significant vibration when I first got my boat, it was also one of the ones underneath so not

immediately visible.

 

springy

Same here.

I tap them with a hammer when working in the engine hole, and any loose ones make a very dull noise.

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Sorry to but in on your post but I still have an engine vibration. Checked the bolts. Recently replaced cylinder head, belts, driveplate, injectors, filters and gaskets. I made this video before I replaced the driveplate and it's calm down a bit but still vibration and gets louder the longer the run. Any ideas

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Sorry to but in on your post but I still have an engine vibration. Checked the bolts. Recently replaced cylinder head, belts, driveplate, injectors, filters and gaskets. I made this video before I replaced the driveplate and it's calm down a bit but still vibration and gets louder the longer the run. Any ideas

 

Can you get a compression test done?

 

Richard

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The last LPWS I heard like that had a failed big end. Unfortunately, the owner had already paid out a lot of money in having a diesel pump replaced. A compression test would have saved a lot of money

 

I'm not saying your engine has such a problem, I'm suggesting a way of diagnosing your noise

 

Richard

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would you say the problem is still there Richard between the 2 videos. People here on moorings are saying its normal engine vibration. I beg to differ and a bit paranoid about doing a trip this year. May have to buy a compression test if I can't find one to borrow.
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Hi there

 

We have an isuzu 38hp on our recently purchased NB. The survey threw up both excessive engine vibration on tickover (recommendation adjust running speed) and also excessive play between prop shaft and stern tube (recommendation replace stern tube). I only have a basic knowledge of engines but I have successfully adjusted the tickover speed. However it only solves the problem in the short term - the engine ticks over too fast IMO and vibration still returns after a while, and is causing lots of other problems (exhaust damage, short circuits, sheared mounting plates...).

 

So, I really need to stop this vibration before I fix any other problems as it is the root cause of everything. We are not planning on getting her in dry dock until next year so i'm guessing attention to the stern tube would have to wait until then.

 

My questions are,

 

Could the vibration be related to the stern tube issue? (Bearing in mind that vibration will still occur out of gear with appropriate revs)

Would replacing the engine mounts possibly help or is that a waste of time/money without replacing stern tube also?

Is it a case of do what you can when you can and slowly eliminate the possibilities?

 

Thanks for looking

 

 

 

Could you post some pictures of the back of the gearbox, shaft and stern tube please.

edited to reflect OPs later comment

Edited by Eeyore
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Thanks for the replies everyone. Don;t worry about hijacking - it's all good education. and you are right to bring up checking the bolts catweasel, because I haven't. However an RCR guy did a few weeks back but no harm in giving them a check and hammer test myself. Eeyore - sorry but that pic is not of my engine, I just posted it to ask what the green (stauff) clamp was as it was quicker than taking photos of mine. So I will take some shots of mine and post them, but probably not for a day or two so stand by!

  • Greenie 1
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Hopefully this pic is of help..

http://imgur.com/fymsyfn

fymsyfn.jpg

Zooming in on the rear right mount clearly shows the adjusting stud way off centre.

That is one very broken mounting, either it got that bad very recently or perhaps the surveyer thought it was supposed to look that way?

Change all four (best practice) as the others will be well past their best with the unequal loading.

The presence of an aquadrive type drive means that the stern tube issue is unlikely to be caused by the mounts. The shaft should be held central in the stern tube by the thrust bearing part of the aquadrive. Check the thrust bearing mounting arrangements for alignment, condition and security.

The engine mounts are urgent, the rest can wait if needed.

Edited by Eeyore
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Great, thanks for the diagnosis Eeyore. Yes the vibration recently got to unacceptable levels so what you say makes sense. So I should press on and get the mounts replaced ASAP. I think RCR quote around 80 per unit - does that sound reasonable?

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Great, thanks for the diagnosis Eeyore. Yes the vibration recently got to unacceptable levels so what you say makes sense. So I should press on and get the mounts replaced ASAP. I think RCR quote around 80 per unit - does that sound reasonable?

I used to work for them, so best to get a few price comparisons from others on the forum or local boat yards wink.png

That said, you'll probably find the pricing to be ok.

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