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Help please - need to understand an engine/prop shaft component


MartinV

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So... update time...

 

The gearbox is officially dead ? 

 

We're waiting for a new one from RCR.

 

Thanks for the nice message about the cleanliness of the engine bay - I'm trying to keep it clean but it's getting this time of year with muddy towpaths! The RCR engineer certainly liked the amount of space to work in though ?

 

Martin

 

 

 

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It wasn't much over at all though - from what I understand it was more about the gearbox wearing out - the overfill was minimal so shouldn't have affected it.  We've come a long way in a short time and before that the boat had been pootling up and down the Glos/Sharpness canal.  It was just it's time.

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3 minutes ago, bizzard said:

Not bad, a bit finiky. The new metal clutch cones need lapping in together of they're liale to slip.

Oh, so they don’t have a clutch material on the cones like a multiplate clutch on a bike? I didn’t realise they were metal to metal. 

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Just now, WotEver said:

Oh, so they don’t have a clutch material on the cones like a multiplate clutch on a bike? I didn’t realise they were metal to metal. 

No metal to metal, I assume so anyway, it was the Technodrive mechanical boxes that I did.

  • Greenie 1
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  • 2 months later...

I’ve got something similar...we’ve in the past had the coupling slipping on the prop shaft and it’s been tightened twice, once by the Canal and River rescue and once (nuts in random order) by me. It’s happened again and this time all the adjustment seems to be used up and still slipping. 

 

Is it just a new coupling needed, and how easy is that to fit, or is the fairly new prop shaft likely to have worn too thin?

 

cheers, dave

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18 minutes ago, droshky said:

I’ve got something similar...we’ve in the past had the coupling slipping on the prop shaft and it’s been tightened twice, once by the Canal and River rescue and once (nuts in random order) by me. It’s happened again and this time all the adjustment seems to be used up and still slipping. 

 

Is it just a new coupling needed, and how easy is that to fit, or is the fairly new prop shaft likely to have worn too thin?

 

cheers, dave

Loctite could be your friend but it will make it very hard to remove it when you have to.

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Thinking about the compression coupling in the back of a Centaflex, where the 6 bolts are, is the prop shaft fully in the coupling?

The rear part is a split cone with the shaft inside, it sits in a conical hole in the back of the bonded rubber bit.

If the shaft is not fully through the split section because it has moved back when in reverse, when it is tightened the split end will have no shaft inside to grip. It does not grip the part you can see.

 

If the shaft is very loose in the coupling, either cutting the splits in the conical end or packing the cone with a shim will allow more bite on the shaft.

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Hmmm. Trying and failing to send a photo. The coupling is brass, attached by 4 bolts to a white plasticky disc (the damper?) which in turn has 4 bolts to the drive shaft coming out of the gearbox. The prop shaft appears to go right thru the coupling but I guess could have slipped forward. 

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6 minutes ago, droshky said:

Hmmm. Trying and failing to send a photo. The coupling is brass, attached by 4 bolts to a white plasticky disc (the damper?) which in turn has 4 bolts to the drive shaft coming out of the gearbox. The prop shaft appears to go right thru the coupling but I guess could have slipped forward. 

That does not sound like a centaflex coupling but the ordinary plastic R&D flex disc with 4 bolts going each way.

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Sounds about right, so it was incorrect of me to link to the earlier thread, sorry.

 

Does that change the picture? I’ve had a chat with a mechanic here on the Stratford, who reckons that if the scoring on the shaft is much, that’s it, out it’ll have to come. In which case, we may as well have it taken out and blacked a year early. Of course the wear might not be so bad, considering we only once gunned it when slipping, and that was a year or two ago.

 

Ah well....

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No problem, don't expect you to be welded to the keyboard.

 

Does the coupling rearward of the white  flex plate look like these?  https://www.asap-supplies.com/propeller-drivetrain/boat-propeller-shaft-couplings/split-half-solid-shaft-couplings   If so a sliver of drink can shoved into the slack coupling before you tighten it will stop it slipping. Many have a keyway and key into the shaft but I've seen lots with no key in!

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Yeah pretty much, except brass (?) not steel. Diameter is approx 1 1/2 inch. There seems to be a keyway but no key as you said. There seems to be no play at all in the bolts, the two halves are just slammed against each other. If the tin can did work, it’d be just putting off the inevitable new shaft I reckon?

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1 hour ago, droshky said:

Yeah pretty much, except brass (?) not steel. Diameter is approx 1 1/2 inch. There seems to be a keyway but no key as you said. There seems to be no play at all in the bolts, the two halves are just slammed against each other. If the tin can did work, it’d be just putting off the inevitable new shaft I reckon?

The up market ones are brass.

 

If there is no gap at all either side in the slit cut lengthways where the shaft goes, I would take it off, make sure the shaft goes most of the way through it, and open up the slit a bit both sides with a hacksaw.

Or if you feel that's a bit involved, release the bolts, open the slit a bit with a few screwdrivers tapped in, ensure that the shaft is well into the coupling, at the very least half way, Slip a couple of bits of drink can or shim steel if you have any in between the shaft and the coupling and bone it all up again.

It is really bad that so many miss out the key, saves all these problems.

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Its a scandal really that gearboxes can just give up and be beyond practical repair. It doesn't happen with vehicles and unless something very odd happens to a car clutch it won't write off anything else. Even if a marine gearbox is 'cheap' it is no reason to accept such a limited lifespan. Horrible things. I had a 'cheap' gearbox that seized after about 10 hours, it had been assembled with too many shims on one shaft, took a couple out and it was ok for a couple of years but that's pretty poor quality.

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Thanks again Sam, I’m not a great mechanic and wasn’t too confident about taking this one on. We ended up calling in a local bloke and he had a hell of a job getting anything to move. The prop shaft had not as we understood been replaced when we bought the boat, and had, as well as general wear including inside the coupling, a significant groove or hollowing inside the gland packing, making it extremely difficult to move the prop forward or back to install the new coupling. So now it’s a new prop and probably housing as well as the coupling. He reckons that the drive assembly (ultimately, the engine mounting) is also out of true. So to bring it up to the proverbial B-O-A-T grand or so, we may as well have the blacking done too, many months early but if it’s out of the water.....

 

That’s turned into an expensive squeaky noise!

 

For good measure, after we’d got it to his yard, we cycled the short distance to the local station, to find that they didn’t stop there on Sundays, and we had quite a long ride instead. The sun shone, all is not lost!

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30 minutes ago, droshky said:

Thanks again Sam, I’m not a great mechanic and wasn’t too confident about taking this one on. We ended up calling in a local bloke and he had a hell of a job getting anything to move. The prop shaft had not as we understood been replaced when we bought the boat, and had, as well as general wear including inside the coupling, a significant groove or hollowing inside the gland packing, making it extremely difficult to move the prop forward or back to install the new coupling. So now it’s a new prop and probably housing as well as the coupling. He reckons that the drive assembly (ultimately, the engine mounting) is also out of true. So to bring it up to the proverbial B-O-A-T grand or so, we may as well have the blacking done too, many months early but if it’s out of the water.....

 

That’s turned into an expensive squeaky noise!

 

For good measure, after we’d got it to his yard, we cycled the short distance to the local station, to find that they didn’t stop there on Sundays, and we had quite a long ride instead. The sun shone, all is not lost!

Sorry that it has turned out to be expensive. but it sounds as though it needed fairly urgent attention before you had a bigger problem.

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