Getting the coupling back on the shaft... in the water - SailNet Community

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  #1  
Old 11-22-2009
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Getting the coupling back on the shaft... in the water

I decided to pull our prop & shaft with the boat in the water, so we could get both shaft and prop checked due to a vibration. This turned out to be a good bet, since it was two weeks turnaround to get the maxprop to/from PYI, now rebalanced and shiny as new.. (we live aboard, so two+ weeks on the hard would be somewhat disruptive)..

I've been test fitting the reassembly before it goes into the water, and I cannot get the coupling back on the shaft.

The shaft guy said that on the hard they usually attach the coupling halves and then use force to bang the shaft back in. He wasn't familiar with the proper procedure in the water.

The coupling is a walter-style split coupling. I've been trying to work it onto the shaft, but it won't go on very far.

I suspect that I need to just bend the halves further apart, I have worked them a little bit by hammering a pry bar in between them. It was on the shaft really tight and was a pain to get off to begin with.

Anyone have any advise or ideas on how to approach this?

Shaft couplings always seem to be a source of pain... I would even replace the coupling if there's a style that is easier to work with. (like maybe something that splits into two pieces?)
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Old 11-22-2009
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I frequently do shaft couplings on pumps and electric motors. This stuff takes a LOT of patience! What I usually find is a couple of small dings. When a shaft gets dinged the metal from the dent got pushed up into a bump along side. I find a new single cut mill file and some very gentle filing does the job. It sometimes takes as much as an hour. You may also find the shaft raised a bur in the coupling. A three corner scraper is good for taking care of that. If you don't have one you can make a serviceable one from an old three corner file on a bench grinder, then stone it.

I was just teaching a new guy how to do it back in the spring on a 75 hp electric motor and pump. He didn't think it would ever go. But a half hour later it slid on like silk. Any time someone tells me they just use a hammer I know there will be hell to pay later. Machinery has a VERY long memory about being abused!

Gary H. Lucas
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Old 11-23-2009
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Patience and precision. . .

I'm with Gary -

It's easy to damage a shaft / hub and not realize it. Since you have the parts in your hand, I'd get the shaft into a lathe and polish it in way of the coupling fit (with fine emery cloth). Also, it probably wouldn't hurt to ream the I.D. of the coupling - preferably with a spiral reamer (so you don't get hung up in the split). You are wise to test-fit the parts in advance. Remember, this is supposed to be a clearance fit - you should not have to use a hammer! If need be, ream out the hub a few thousandths larger. Good luck!
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Old 11-23-2009
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Ditto what has been said above. The coupling should slide on smoothly. If it doesn't then check the shaft very carefully, you will probably find a few small dings that you may not even be able to really feel. As suggested above, a fine file or emery cloth and some time will usually fix it. I would be careful about prying the coupling apart very much, unless you want a new one.
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Old 11-23-2009
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I did sand away the layer of rust on the inside of the coupling so that is smooth metal now. Gary -- I can see where there's scoring on the inside of the coupling from the set-screw dimple in the shaft. I'll check if I can get rid of that.

Will also try the emery cloth or a file on the shaft and see how that goes. There wasn't anything obvious that it was catching on. I can get it on maybe 1/8" and thats it.

The shaft guy I had check the shaft when it was out thought that it was okay for it to be tight, so I may take it to another shop to get a second opinion and see if they can do anything.. There's not a tonne of space to work with when the shaft is back in the boat, so it's worth it to me to ensure this goes smoothly

Bellatrix -- as for reaming the coupling out, not a bad idea though I'll probably hvae a shop do that since I don't have the tools and I want to make sure I don't affect the runout or end up with the coupling off center. FWIW even a few thousands can be significant here.

Thanks for all your replies.
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