Self-ejecting propellor shaft coupling

I wonder if the thread is bottoming out, maybe with the wear on the shaft & 'fingers' .

I suggest, as it is now, mark on the shaft the position of the nut, remove the tapered ring & screw the nut back to the mark, will the nut screw on further ? if not, get a thick washer or make 1, place it between the nut & ring.


can't be doing the seal much good
 
From what I have read here applied to what I have observed aboard:

The shaft does not spin in the coupling, the bronze woodruff key prevents that until the shaft has been ejected. I don't think the "fingers" are bottoming out, i.e. touching as there is no wear on the shaft as such to give the necessary slack to allow this, a possibility is "stretch" on the cone packer that forces the cone to clamp onto the shaft allowing the nut to bottom on the thread, that had already occurred to me and also the solution of adding a further shim washer to prevent that - well done starfire.

However, it certainly looks as though toothy, misterg, and Vics have the rights of it here, the required torque is just not achievable with a lump hammer and punch and that is the problem I need to address. I'm going down this morning with a micrometer set to mike up everything and bring back the nut to redress the notches. I'm then going to make an attempt to source a very large C spanner indeed - family can go on a crash diet to pay for it (only joking!).
 
Just a thought..........couldn't you hire a C spanner? Would be worth a call to your local tool hire company......you might be surprised.
 
Not in reverse

Hope you get It sorted .But . I hope there is somthing stopping the shaft drop out of the boat In reverse!! 25 years ago I knew someone with a similar shaft coupling .Actually he did not know what happened initialy.He was in reverse when engine revs went up drive stopped and he bumped into another boat by the time he sorted the bump out he had 18 inches of water in the engine compartment and he couldn't see what had happened. He nearly lost the boat. He put an anode on the shaft inside as a collar when the new shaft was fitted ..the shaft seal on his boat was a a stuffing box with grease so nothing on the shaft to stop it.
 
toothy said:
Ok here is my two cents worth, I work as a millwright on ski lifts and we use this kind of nut a fair bit we call it a ring wrench you should be able to find them at a reasonable price somewhere locally. 217 foot lbs is 217lbs 1 foot from the center of the shaft if you apply 70lbs or so 3 feet from the center of the shaft you have your 217lbs give or take. The point is that it is a taper and too much force you will split the sliding taper, this is also a dry torque so if there is any lubrication on the threads you will be in danger of applying too much torque resulting in a split taper or stripped threads. I would clean up the shaft as best you can do not knurl it or any other hokey hammer stuff. Assemble making sure there is no lubrication around and torque to the recommended amount at this point there needs to be some clearance between the fingers( at the small end) if not then the taper has bottomed out, probably because too much material was lost when the shaft spun during the original incident. See how you go with that if it still spins then you might be able to get away with a sleeve to take up some of the clearance you have. also check all the gaps between the fingers to be sure that loose material is not blocking the taper from closing up.

Good Luck
Click to expand...

Correct on all fronts. I was in charge of maintenance for a drilling rig where we use a lot of motors / shafts / couplings. The tapered clamp relies on friction to keep it all together and in particular surface area. If you rough up the shaft you actually reduce the surface area as the "fingers" clamp on the peeks of the roughed up bits. The high torque is required to provide the clamping force by the fingers and therefore is an indirect method of securing the shaft. Its very easy to apply the correct torque but if you don't get the longitudinal movement then you don't get the required clamping force i.e. the torque force is consumed by something like dirt on the threads.

I have experienced many situations where simply dismantling and cleaning has addressed the problem where torque does not work. Over torque and you compress the fingers and plasticaly deform them or the shaft. The shaft only moves a little and the grip is lost. The grip requires a certain amount of elastic movement is the shaft / fingers to retain its grip. Hence, hammering the **** out of it with a ball pean hammer and a punch is not a good idea.

If the diameter on shaft or fingers is out of spec then you have no option but to replace.

Your shaft may be slight bent as well which is applying a cyclic load which shakes the clamping arrangement loose.
 
self ejecting prop shaft

Given all that "C" spanners etc, etc, a couple of alternatives, One- to file a couple of flats on the nut and use a "normal" spanner to torque it up (having cleaned out the fingers and roughed up the shaft. Two, do fit something to the shaft so that should it become loose once again (I presume it has already) like an anode (as has been mentioned already) or just a simple jubilee clip. to stop the shaft going completely out of the stern of the boat.
 
If after re-inspecting you come to the conclusion that the drilled hole in the shaft with a roll pin is an additional possibility,then get a cobalt drill to drill the shaft, it'll be harder than you think for ordinary HSS or Ti surfaced drill bits. Could be a belt and braces option too anyway if torqueing not fully achievable

ianat182
 
I've actually located a C spanner on a racing (cars that is) tools etc supply outfit. Price incl. vat and postage a surprising £16. I say surprising because my first searches threw up prices of £35 - £50 so not a joke.

E-mailed the company querying if I could sleeve a scaffold pole over it to achieve the desired 217ft/lbs torque mentioned by VicS, fully expecting a rasberry if indeed any reply at all.

Delighted to get a mail back from the Sales Director (clearly a fellow bodger) to say he'd done just that on a smaller size spanner than I needed, and estimated he'd applied a force of over 230ft/lbs before budging what he was forcing without deforming the spanner. He went on to say that the manufacturer does not state maximum force the tool will take but in his opinion I would not have any problems.

I've ordered one!

When it arrives I promise to take on board the advice of the two engineers and thoroughly clean the fingers of the collet and the shaft, paying particular attention to the gaps in the fingers, lube the sliding tapered washer as reccomended by VicS' link to the Vetus manual, and properly jam the coupling so as not to bugger the gear-box when torquing up. Only downside is now having to remove heating ducts etc fouling the access for the scaffold pole!

If this does not work, I'll drill with one of my 6mm cobalt drills and pin the bugger with a roll pin (shorter than the compressed diameter of the collet of course and if that fails, well, I've got a large generator and a genie hoist in the workshop plus a large arc welder and I'll..........well.........the rest to your imagination.

As an aside, the shaft cannot come completely out because it (and the prop) hit the rudder which prevents that and, which, on last lift out to clear the rope, has the scars to prove it.
 
Instead of a roll pin, you might get away with a drilled and tapped hole in the coupling, and a dimple in the shaft to accept the end of a bolt. Perhaps two, one each side, but would save drilling through the shaft.
 
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