Damaged shaft fit to coupling help?

[thruska]

Originally Posted by Cadence

Did I totally misread the original post. It appeared getting a flange off was hard and getting a new one on was the problem.
Trying to machine a shaft with a file is Ludacris. Heat the flange hit the shaft with a blast of CO2
Sorry if I misread it but that's machine shop 101.
New coupling freshly machined. I would suspect it prior to the shaft. JMHO

I agree but when slipping yhe hot coupling on be wuick and have a mark set where you know it belongs. A hot part met with a cold part will shrink the coupling quickly

[captlloyd]

Yes, you can and should hand fit the coupling with a file if you need to. File should be a fine file, not coarse. Use it in a back and forth motion at the same time rotating it partially around the shaft. As stated before clean before checking each time, a tiny filing can stop the coupling from going on. Emery cloth is good in a back and forth action around the shaft. As you gently tap the coupling on, it will stop at a high spot and leave a mark. This is a high spot. File it off. Keep going until the coupling goes all the way on. Also you should be using a key if there is a key way. You may have to fit the key also. If the coupling was on the shaft previously, there should not be that much fitting to do. I don’t recommend heating the coupling to get it on, it will cause you problems when you want to take it off. And yes, always use Neverseize.

[Fore and Aft]

Sounds like a machine shop job to me. That coupling has to fit tight on the shaft without any play. You have already paid for a new coupling so break out the wallet and finish the job properly.
Cheers

[Warby12]

Hi there, I've tried the filing and very careful measuring but not making any progress.



We are out of the water which is good but the shaft cannot go past the skeg, so it is looking like I will need to raise the engine


Also although I do 99% of boat work myself, I have given up, too nervous about getting it on and then having more serious misalignment (breakage) issues later. The whole point of the solid coupling was to get more accurate alignment, which the old flexible coupling wasn't giving us.



Time to call a pro, fingers crossed

Thanks for your help!!

[Iaangus]

Originally Posted by Warby12

Hi there, I've tried the filing and very careful measuring but not making any progress.



We are out of the water which is good but the shaft cannot go past the skeg, so it is looking like I will need to raise the engine


Also although I do 99% of boat work myself, I have given up, too nervous about getting it on and then having more serious misalignment (breakage) issues later. The whole point of the solid coupling was to get more accurate alignment, which the old flexible coupling wasn't giving us.



Time to call a pro, fingers crossed

Thanks for your help!!

Take a deep breath, this should very easily be rectified. The fact that it is a tight fit is a good thing. A loose fit would be much more problematic. First you need to make sure the coupling is machined to the proper size for the shaft, use a vernier,digital or dial caliper for this. Measure the inside of the coupling and the diameter of the shaft. The measurements should be about the same give or take .001. Use a small half round file to put a small bevel on the coupling if there is not one, Use a flat file to put a small bevel on the shaft if there isn’t one. At this point the coupling should at least almost fit on the shaft. If it doesn’t, providing it’s the correct size, you just need to prepare the shaft for assembly. You need a long strip of emery cloth sold in rolls for exactly this purpose. The rolls are about 1 inch wide, you can use 80 grit, this is a fairly aggressive grit that will remove metal quickly while it is fresh but will be less aggressive as it wears for a smoother finish. Tear off a 24 inch long strip of emery paper soak paper with a penetrating type oil (WD40 or what ever is handy or cheap) wrap half way around shaft and pull ends in an opposing manner. Rotate shaft 33 degrees and repeat. After this repeat one more to complete. At this time you are just trying to remove high spots, be careful to not remove to much material. Repeat this procedure till coupling fits turning shaft often. Best fit would require a mallet to tap into place, use anti seize for final installation. I must disclose this is standard procedure for general machinery repair but I have very little marine repair experience.

[billknny]

Originally Posted by Warby12

Hi there, I've tried the filing and very careful measuring but not making any progress.



We are out of the water which is good but the shaft cannot go past the skeg, so it is looking like I will need to raise the engine


Also although I do 99% of boat work myself, I have given up, too nervous about getting it on and then having more serious misalignment (breakage) issues later. The whole point of the solid coupling was to get more accurate alignment, which the old flexible coupling wasn't giving us.



Time to call a pro, fingers crossed

Thanks for your help!!

As painful as this is it, is a good idea. This is an important part to have right.

Just to give you a feel for the best approach, anytime I have had to replace a shaft, I always buy the shaft with a matched coupling--one that was machined in place on the shaft to be 100% certain that it is both has a common center to the shaft, and that the face is perpendicular to it.

That kind of attention to detail is not absolutely required, but it means that things WILL fit and WILL align quickly and correctly.

I once spent most of a day trying to align a new shaft and coupling that had 0.005" of runout. That was a frustrating pain in the butt that I will never repeat.

And there is a very special place in hell for every ignorant boat builder who builds a boat that requires moving the engine for something as routine as pulling the shaft. Why would anybody do such a thing? It is one of our amusements, pointing out boats in the haul out yard where the shafts can't be removed. So common, so stupid.

[Warby12]

Thanks again everyone. I really appreciate it

I got the shaft out (lifted the engine). I think i might have been able to get the shaft out backwards if the cutlass bearing wasn't glued in! Next time i do a cutlass I will fit grub screws. Just not enough play to get it past the skeg.

Now to find a machinist in Brisbane / Gold Coast

[dfelsent]

While you are at it bring the prop, coupler, shaft and any keys and the prop nut to the shop. Especially if it’s a marine place.
They can machine the three parts to a match and make sure the flange is perpendicular to the shaft. They can make sure the prop and shaft tapers are correct.

[Warby12]

Thanks, I think I found a good place, a knowledgable friend recommended them Watson Marine in Coomera. For a guy who lukes to do everything, it's nice sometimes to hand it to an expert when you're beat.

They are going to chceck the shaft for bends first, then skim the end until it's on, then tighten it up and face it

[RaymondR]

Originally Posted by coopec43

I assume the shaft has some high spots?

If that is the case I'd get a good quality file and file the shaft forward and backwards to try to find the high spots and then file the high spot. I would make use of my high quality vernier gauge as well. That's pretty agricultural but what else?

It's called "draw filing" and you should pick up the high spots fairly quickly.

The two most common distortions are the end peaned over from being struck and the outer edges of the key slot swelled out from torque on the key if the slots are too large for the thickness of the key. Both easily cured with a bit of draw filing.

The best type of flange for use on stainless shafts are the ones with slots down the side of the boss which allow tightening onto the shaft after installation.

[Hoohaa]

Hi Warby.
Just read this thread and was wondering. What's going on with the shaft to make you want to install this coupling to get a better alignment?
I ask this because I have a center cockpit boat and have gone to huge lengths to achieve a near perfect alignment. All to remove a wobble in the shaft. Are you having similar problems?

[Warby12]

Thanks Raymond, I actually find this stuff really interesting, It's a real gap in my knowledge, maybe because precision metal working requires expensive machines?

By drawing the file back and forth, do you mean in line with the shaft?

The coupling I was trying to fit is like this Poly Flex Group - Advanced Polymer Technology for Vibration Control - 434 Parallel Clamp Coupling
Is that what you mean?



Hoohaa, the old coupling, that came with the boat, was this one https://www.vetus.com/en/flexible-co...aft-30-mm.html
It is really hard to align because of the rubber bushes. We removed it to replace a leaking shaft seal, (it had to be cut off because there was no way to hammer out the retaining pin ) We replaced like for like. When I had the shaft measured for a new coupling to be machined, I don't know what happened, but I had to get really nasty with a big hammer to get it on the end of the shaft (hammering the coupling not the shaft) so I've always been uncomfortable with it. I think the shaft was already damaged, maybe around the now unused keyway?


So, we have a large but finely pitched prop, so it spins fast, maybe alignment vibration has caused us to chew out two shaft seals, a lip type seal and a "deep sea" dripless seal. We've now bought a PSS, so I want to make sure the shaft is straight, and aligned perfectly

[Hoohaa]

I had the same solid coupling. Probably a stupid question. But did you try driving a small wedge in to spread the coupling while you tried to slip it on?

Regarding the my previous question. I have a 2.3m long shaft which is only supported at the rear strut and at the gearbox. This has caused the shaft to sag a bit and develop a small wobble. My final solution is to put a second cutlass bearing into the forward end of the stern tube which will give it third support along its length. I just thought it might be worth considering if this is a problem for you and while you have your boat on hard.

[RaymondR]

Originally Posted by Warby12

Thanks Raymond, I actually find this stuff really interesting, It's a real gap in my knowledge, maybe because precision metal working requires expensive machines?

By drawing the file back and forth, do you mean in line with the shaft?

Backwards and forwards longitudinally with the file at right angles to the centreline of the shaft.

The coupling I was trying to fit is like this Poly Flex Group - Advanced Polymer Technology for Vibration Control - 434 Parallel Clamp Coupling
Is that what you mean?

Yep, that's the one.


Hoohaa, the old coupling, that came with the boat, was this one https://www.vetus.com/en/flexible-co...aft-30-mm.html
It is really hard to align because of the rubber bushes. We removed it to replace a leaking shaft seal, (it had to be cut off because there was no way to hammer out the retaining pin ) We replaced like for like. When I had the shaft measured for a new coupling to be machined, I don't know what happened, but I had to get really nasty with a big hammer to get it on the end of the shaft (hammering the coupling not the shaft) so I've always been uncomfortable with it. I think the shaft was already damaged, maybe around the now unused keyway?

The Vetus one looks like what is referred to as a taper lock. The conical bush is forced down into a matching hole which forces the tapered bush to contract and grip the shaft. They are usually easy to remove.

So, we have a large but finely pitched prop, so it spins fast, maybe alignment vibration has caused us to chew out two shaft seals, a lip type seal and a "deep sea" dripless seal. We've now bought a PSS, so I want to make sure the shaft is straight, and aligned perfectly

I used a PSS on my last boat and was very happy with it. One of the things I did was run an air vent from the fitting on the PSS up to just under deck level so that any air in the stern tube could vent. It's the sea water which serves to lubricate the working surface between the SS collar and the carbon bush.

[Zach]

Machine shop was a good call.


If you run into this in the future, you can take the old coupling that is assumed to be faced to the shaft and put lapping compound on the shaft without a key in it and turn it over 10 or so times. Wipe it off, and the shiny spots are your high spots. When they are no longer raised up nicks and hard edges, try the new coupling.



Most of the time it doesn't take a whole lot of lapping, and it keeps you round/concentric to the surface that is faced.


Then you can take some prussian blue, slather the end of the shaft in it and slide the new coupling on. Where it is hanging up will take the blue off.


You can do the same thing for the prop end of the shaft, as the taper isn't always cut the same on both the shaft and the prop even though they are supposed to be.



Last up, if the diameter of the shaft is too small for the wheel you are turning, you can have shaft whip and even an aligned shaft will eat the seals out of the stuffing box when you run her hard. If you get a distinctive thump thump thump through the whole boat at certain RPM, you can have a perfectly aligned shaft alley and no bent shaft... but the whip in the shaft is trying to eat your stuffing box tube.



It is more work to oversize things, than it is to add a support with a pillow block bearing internally, but a lot of sail boats end up with a 5-7 foot long 1 inch or 1 1/8 shaft, that works... but has a 4 to 5 foot unsupported span.



The shaft gets sized for the horsepower, but not the length.



The maintenance cycle of stuffing boxes and cutlass bearings is a lot more than if it had a diameter meant for its length, or a motorboat style shaft tube that supports it right up to the last foot before the coupling.


Two blade props kind of vibrate like a paint stirrer, in that they can be balanced, but are always out of phase to everything around them when ever they fall behind a shadow of a strut or aperature. Three blade props run smoother, as you can balance them a bit.