Prop Shaft Problems

[Chloe]

We have a Liverpool boat with an Izuzu engine with a problem The shaft has slid out of the split coupling. It did happen years ago when we picked something up on the prop. We have had a quote from a marina who have suggested it will cost about £600.00 (which we havn't got).

 

Why can't we slide the shaft back into the coulpling and retighten everything. The mechanic has suggested that there is no bite in the split coupling and the end of the shaft is worn. He further suggests that all thiis needs replacing and it will have to come out the water..

 

My question is there an alternative way to solve the problem that is cheaper and acceptable.

 

We do not want to codge it up!

[RLWP]

Very hard to make a decision without seeing the parts, which the marina mechanic already has

 

Richard

[Roger Crown]

It sounds a lot of money. Breaking it down, docking the boat and then the cost of the parts you mention are hundreds, so it seems a reasonable quote.

 

Mate of mine had a similar problem, Liverpool Boat, Isuzu engine.

 

He made a successful claim on his insurance.

 

I think he may have had a similar experience to you.

 

His propeller hit a large tree trunk under the water .

 

[Kwacker]

Could it not be shimmed, or the shaft dot punched where the coupling grips it?

[b0atman]

Try your way first maybe it will hold then budget it in with blacking the boat.

[Kwacker]

Yes, my suggestion would be a get-you-by until the boat was coming out anyway.

I have used the dot punching technique to swell an undersized shaft on many occasions, always as a get-you-by, but on most occasions it has lasted for years.

 

Stop smirking at the back!

Edited November 25, 2014 by Kwacker

[Roger Crown]

Good suggestions from the other guys, well worth a try.

Downside is (sorry guys) if you make a do and mend it could go at the worst time, miles from help etc etc all adding to the ultimate bill.

 

Roger

[Kwacker]

Fair point, I suppose it depends on the workload and how long before it's coming out anyway.

[magnetman]

Like reversing hard to avoid an impact of some sort.

 

I'd be tempted to get it sorted out but maybe get a second opinion to make sure you aren't being had.

[Bee]

I would indeed shove the shaft back into the coupling, tighten the bolts and see if it feels reasonably firm, if you have mains electric I would get the trusty electric drill, a couple of new HSS bits, some oil and drill right through the whole lot and put a nice big bolt through it, I did this with a hand drill years ago on a boat and it was a permanent fix. If you take the coupling to a machine shop they can even drill a proper vertical hole in it leaving just the shaft for you to drill. Carry a spare bolt or two and if anyone asks just say its a vertical keyway and accepted engineering practice in Shropshire.

[nb Innisfree]

I would indeed shove the shaft back into the coupling, tighten the bolts and see if it feels reasonably firm, if you have mains electric I would get the trusty electric drill, a couple of new HSS bits, some oil and drill right through the whole lot and put a nice big bolt through it, I did this with a hand drill years ago on a boat and it was a permanent fix. If you take the coupling to a machine shop they can even drill a proper vertical hole in it leaving just the shaft for you to drill. Carry a spare bolt or two and if anyone asks just say its a vertical keyway and accepted engineering practice in Shropshire.

Trying to aim for the bottom hole will be ht or miss, better to have just the top hole drilled, that way the shaft hole will be inline with the other two when you drill through and give a snugger fit, better than a central but loose fit.

[boots]

We had a similar issue with the same set up - the prop would slip in the coupling. So yes, we tightened the coupling and all was well for a while. Eventually it happened again and this story repeated itself, becoming more and more frequent until we could tighten no more.

 

At this point we called into a marina and a new coupling was ordered and once fitted all was well...until....

 

We started to have problems with the gearbox (prm) which would not engage reverse.

 

 

Eventually, the fault was found to be:

 

1. Previous owner is believed to have had a prop fouling - new prop & shaft had been fitted

2. However, drive plate and gearbox had also been damaged and the shaft was out of alignment

3. The resultant vibration etc was most likely to have caused the wear, and issue with the coupling.

 

Since these issues have been fixed, no further issues but afraid to say it wasn't a cheap experience.

 

(Liverpool boat, Isuzu 35hp, vetus stern gland)

[Bee]

Damn, you could be right, you'll be telling me they can read micrometers in Wiltshire next.

[Timleech]

When a shaft coupling works loose, it's often a consequence of poor engine/shaft alignment. Whether you try to keep going with what you have, or spend the money on new parts, get the alignment checked.

As Richard says, it's impossible to offer a proper opinion without sight of the parts.

 

Tim

[Guest]

Dont know if this would work, but on electric motors we would sometimes get our turner to "knurl" the shaft in order to make a coupling grip again. Certainly worked on powerful electric motors etc. Obviously the boat would need drydocking.

Think I would go with a bolt personally.

[Taslim]

Damn, you could be right, you'll be telling me they can read micrometers in Wiltshire next.

What? One can read a precision G clamp. Whatever next?

 

I prefer those small spanners with numbers down the handle. You can lock them to the nut size but 'not sure you could get enough torque to bind a prop shaft coupling though.

 

A little more serious. Some older cultivation kit used shear bolts through the coupler & shaft as sugested by BEE. Dont use high tensile bolts & carry spares.

 

If, as suspected, the shaft et -all will need replacing in the end it's got to be worth a shot as a sensible quick fix.

[ditchcrawler]

Dont know if this would work, but on electric motors we would sometimes get our turner to "knurl" the shaft in order to make a coupling grip again. Certainly worked on powerful electric motors etc. Obviously the boat would need drydocking.

Think I would go with a bolt personally.

We use to do the same, surprising how slake they can be you you still get away with it.

[Chloe]

Thanks for all the advice.

We will consider everything that's been said.

We are tempted to go with drilling a hole and using a verticle shear pin, if this would be seen as an acceptable engineering practice to a surveyor.

[Kieron G]

Could you find a deeper nylon drive coupling or a 4 inch spacer to make it deeper ( if that's the size ) and shorten the shaft with a cutting disc in an angle grinder then you will be gripping a fresh section of the shaft.

[magnetman]

A bobbin coupling ?

 

http://www.asap-supplies.com/marine/bobbin-shaft-spacer-couplings

That might do it keeping the bottom of the boat underwater where its meant to be

a slitting disc on a decent 4 inch angle grinder goes through a 1.5 inch stainless shaft pretty quickly in my experience

Edited November 26, 2014 by magnetman

[Naughty Cal]

Think yourself lucky. Its just cost me £865 just to buy a Volvo Penta shaft. And thats with us fitting it ourselves

[Boat&Bikes]

If it was mine I would drill and tap a couple of holes through the coupling and use grub screws to bite into the prop shaft. Will give you the drive but still should slip if your prop ever hits something solid. Easy job and cheap.

 

Ian.

[kris88]

Think I'd try a brass shim,but only till the next time the boats out of the water.

Regards kris

Edited November 26, 2014 by kris88

[nebulae]

We solved the problem with our Isuzu set up by fitting a Python Drive. Requires a plate welded in to take the thrust bearing. As we welded it ourselves when the boat was in dock,the cost was only the Python drive .Otherwise,allow three hours for fabrication and welding. The Python drive uses a three part shaft clamp,which has so far given 2,500 hours with no trouble.(Also helps with miss alignment issues and removes thrust from the gearbox)

[ditchcrawler]

We use to do the same, surprising how slake they can be you you still get away with it.

Thinking about this I think we used a hand held Knerling tool, we also did the internals on the motor end where the bearings went in. Some times we used a type of glue Bearing Lock