shaft thump

[ian1]

I have a Colvic 20 which has a Vetus 10hp twin cyl. this is my 1st boat which I have had for 4 years, the prop shaft exits thro the keel via a gland, there is no P bracket, at approx 1000revs a very pronounced thump starts either from the shaft or the prop, increase the revs and it goes away, there is quite a bit of lateral play on the shaft at the gland , before I start to remove the shaft is it likely that there could be a bush or seal in the gland , can anyone clue me up before I start.

 

[sarabande]

Do you have a cutless bearing at the outer end of the shaft ahead of the prop ?

Can you move the prop up and down, or sideways ? About 1mm play will be OK, any more and the cutless is suspect.

Do any other parts of the transmission move in any non-rotary way ?

 

[john_morris_uk]

I have experienced this where the shaft is hitting the sides of the stern tube due to misalignement and and engine that is jumping around on its engine mounts. Symptons are identical anyway... Assuming that the cutless bearing is ok, try checking the engine alignment?

 

[Tranona]

Sounds very much like a worn cutless bearing. Is there a bronze housing bolted to the deadwood where the shaft exits? If so, just remove the prop, undo the screws locking the housing and unscrew the whole housing and it will slide off. The cutless bearing is inside. To replace remove the grubscrew that stops it from moving, press the bearing out and replace. Make sure you measure the shaft accurately - it is almost certainly 1 inch or 25mm, but they are different by enough (0.4mm) to make a difference.

If the cutless is all internal you will need to take the shaft out and use a special extractor. Time to call a marine engineer if you feel uncertain about how to deal with it!

If you can post a photo and you will get more specific advice.

Hope this helps

 

[vyv_cox]

Also ensure that the shaft is not excessively worn in way of the cutless bearing. Fitting a new one can be a waste of time and money in this case. I am about to fit a new shaft because of exactly this problem. The new cutless bearing that I installed two years ago was an improvement for about an hour. The knocking then went back to just as bad as before.

 

[Mrnotming]

Hi Mac 1,Had a knocking problem with a friend's boat and began by loosening the bolts on the half coupling. then the stuffing box was opened and found that the packing was compressed on the down side. took out packing, then supported shaft centrally in the box from under with a small jack. repacking followed, and then finally quite an amount of work on the engine mountings to raise the engine back to where it was within about .005.in tolerance all around the half coupling. retighten bolts.This removed the knocking. I recall checking for bent shaft as well during the operation! the engine mounts lose elasticity over a small number of years, and usually the one nearest the fuel pump is worse for wear than the rest.hope this helps. Another time, another boat I removed a bushing in the exit part of the shaft log to allow the engine to move about a bit more. this cured the oven rattling!The shaft was short so the extra support was not needed as an intermediate bearing in this case.best of luck!

 

[rjp]

I'm in exactly this position, some wear in cutless bearing but looks like the shaft is worn too so probably going to have to source a new one.

There was a thread a few months back where somebody suggested a good supplier, but the new search engine won't let me find it! Can anyone remember or suggest? I'm in N.Wales so that would be ideal, but anywhere would be useful.

John

 

[Tranona]

Suggest Norris in London or Lake Engineering in Poole. Both do mail order and shaft and cutless can be ordered safely remotely if you measure what you want accurately.

However, I am sure there will be somebody more local if you want to deal face to face. Try the big yards like Dickies as they will know.

 

[vyv_cox]

Mine came from Lake Engineering, here Have dealt with them a few times, they seem reliable and accurate.

 

[rjp]

Thanks for the helpful replies. Just what I needed.

John