Shaft Coupler

Maine Sail · Nov 10, 2008

Rich (P303) said:
You know... I don't know why I type these questions. The more I type... the more I know the answer... and just want someone to tell me the easy way out.:cussing:

I have a 1984 Pearson 303 and had a problem with the packing gland over heating on the shaft this year. It turns out it was due to excessive vibration where the shaft goes into the coupler.

I had 2 captive screws on each side of the coupler that were wired... however wired loose. I tightened up and wired again... problem went away.:dance: After further investigation... while boat is now in yard... it appears shaft may have backed out of coupler maybe 3/8 of an inch tops, by looking at the shaft near cutless bearing.

Does anyone know how the shaft is attached to the coupler? Besides the keyway... do the to opposing set screws in the coupler just bite into the shaft... or bit into a dimple or kerf on the shaft?

The French in me says... loosen the setscrews and start banging away on the prop end of the shaft until the shiny area disappears into the cutless bearing and tighten things back up. (Possibly damaging the transmission?).

The smart part of me says disconnect the coupler from the shaft saver... to separate from transmission before attempting such a maneuver; and/or replace coupler; replace cutless bearing and rubber hose while I am down there.

Any suggestions Mates?

I have the smileys covered.

You answered most of your questions.

The only one not answered or asked is that you may need a new shaft and coupling. A straight coupling has an interference fit or light press fit. If it wobbled and or came loose it's toast and the shaft may be too.

Here is a post from a week ago that will give you more info than you need but...hey why not!

Some input on couplings.

1) If you are removing a coupling that is more than say two years old, depending on bilge moisture, you should not re-use it. Solid couplings are a one time use after they have become "made on" as Mike the manager at H&H Prop refers to it as! Why is this?

When you remove an older coupling you will break a layer of rust free. This rust was your tolerance. A shaft and coupling are meant to fit together very, very snugly. In all my years of boating I have only had one coupling go back on and maintain the tolerance and that boat only had a few months of service on her. Re-installing a used coupling can ruin your shaft. Shafts are expensive coupling are cheap in comparison!

H&H Propeller, the machine shop I use & the largest shaft and prop shop in the North East, fits the coupling to the shaft with a tolerance of .0005". On a properly machined shaft, without any anti-corrosive agent like Tef-Gel, it will slide on about a 1/4 to a 1/3 of the way before you experience some serious resistance. This initial fit is often referred to as "lead" meaning they give you a little bit of leeway to get the shaft started into the coupling. The coupling and shaft are machined to exacting tolerances (.0005) so there can be NO wobble or play between the shaft and coupling. Any wobble will cause excessive shaft, key and coupling wear and could eventually lead to a failure.

2) The shaft is usually fine and can be cleaned and re-used. It is the steel coupling that gives up surface material, and this lost layer of rust means you can't re-use it. If the coupling just "slides" back on it is too loose!

3) When reinstalling a new coupling to an old shaft you should always have it fitted and faced by a machine shop or prop shop. H&H Prop charges $65.00 for a fit and face. While you are at it have the shaft trued. Shaft truing is more costly than a just a fit and face but a lot cheaper than a new shaft and it will get rid of any annoying vibrations. Another good practice to eliminate bvibrations is to "lap fit" the prop to the shaft and you could actually do this yourself.

If you hit something and bent the tapered end of the shaft near the prop the shaft is toast and most any reputable shop will not and should not straighten it.

4) When re-installing the shaft you should get it started with the machined in "lead" then lightly tap it home with either a rubber mallet or an oak or maple block protecting the shaft and a hammer. For this job need two people or many trips up and down the ladder. Pound it in while looking in the coupling holes until you see the dimples for the set screws. Don't over do it cause backing it off is more of a paint than driving it in.

5) Shaft keys should fit snugly but not so snug that they are "key bound". If the key has any play have a machine shop make you a new one.

6) Anti-corrosives like Tef-Gel can sometimes aid in future removal but it is no guarantee. As Mike at H&H says about using Tef-Gel or any anti-corrosives/seizes "It won't hurt nothin' but a properly machined shaft and coupling should shave any thing you put on that shaft off as you fit the two together". He says it won't hurt but in most cases it won't help either. You should also not use a neverseize product containing any aluminum, copper or graphite as it can add to galvanic corrosion issues.

Contrary to what Mike says I have been using Tef-Gel and had good to mixed results up to about two years with coupling removal. It does aid some in the removal but does not always mean it's re-usable. I will be pulling my coupling in a few weeks to do some tranny work, and it is also at the two year mark, and this time I will photograph any rust or lack there of.

7) If you can, I can't I have a v-drive, don't replace the coupling with a solid coupling and instead replace it with what's called a "split coupling". This will make future removal and re-install much easier. Even with a split coupling you should still have it fitted and faced after removal. The $65.00 +/- is well worth it.

Hope this helps..

Oh and;

Never use a hammer to pound directly on a coupling that is connected to the tranny. You can damage the bearings and the soft aluminum cases many transmissions are made of.

sailingandsuch · Nov 10, 2008

Rich - I personally do not know the answer to your question. But, I think I can help you with it anyways.

On my website(which is in my signature), I have a few links to some Pearson websties. Quite a few actually. I even have some articles about the shaft and packing that you are refferring to. You may try visiting each site because the Pearsons may have been constructed in the same way around the shaft and such.

If you visit, go to the Sailboat Projects section and scroll down the page to engines. Also, check out the Restorations and Modifications pages, they both have links to websites about Pearsons.

Good luck with your project!

Ross · Nov 10, 2008

Rich, when I assembled the shaft to the coupling I put the assembly on the drill press and drilled dimples in the shaft at the set screw holes. There are two good reasons for doing this. 1st, it avoids raising a burr with the set screw that will interfere with removing the coupling from the shaft. 2nd the dimple provides positive locking of the shaft to the coupling not just depending on the "bite" of the set screw.

Ed Schenck · Nov 11, 2008

Dimple it like. . .

Ross suggests. Do drill dimples or deepen them if you find them there. Was reminded of the importance of this when we almost ruined the bellows of the dripless box. This would have let a lot of water into the boat.

We were delivering a boat when encountering a crab pot line(honest, I was not driving). After diving, clearing the line, and starting the boat, no forward motion! Found that the shaft had been pulled out of the coupler. And far enough to collapse the bellows. Turns out the mech who installed the dripless stuffing box had not lined up the set screws with the dimples. And the dimples were barely perceptible. I drilled new ones after we reached the Marathon YC.

Now you have me wondering about my own boat.

Hermit Scott · Nov 11, 2008

Just bang it back in with a 10 lb. sledge...it will be fine.

I just had this coupling made today. It was like an 8 hour job in a machine shop, but the guy apparently felt like hooking me up. He had one of his guys do it anyway. This one was $150. It's 304 stainless. I had them ream a hole through it for a 1/4" pin. It also has 2 set screw holes. The hozzel, I guess I would call it is machined to be longer so no play is possible. This one does not hammer on. It will slide on with a little wiggle so long as it's clean.

IMHO, as they say here, the fact that it slid out would not determine to me that it is toast.
The determining fator to me would be a dial indicator. I would do what ross did to his, drilling dimples into the shaft, then I would buy new set screws and torque them back down. I would put a dial indicator on it to see if it's out of center.
If you can't sleep at night worrying about the shaft and prop pooping out into the deep, you could always put a collar lock on an inch or so away from the packing gland. There's a pic of one. This one isn't stainless, but it's made to spin on a shaft and not cause vibration.

However, you said you had other problems going on. I have no idea what a cone is, but if your output shaft is spinning concentrically and so is the shaft, and it's mechanically locked in place, vibration will not be coming from there.

By the way I was just joking about banging it back in.

Maine Sail · Nov 12, 2008

Hermit..

There should be no wiggle and it should fit tightly. Perhaps this is why it is best to use a shop that understands and specializes in marine prop shafting. Any, even a little bit of allowable wiggle, can turn into a worse wiggle and shaft or coupling wear and in a worst case, a failure.

You don't have to worry about your prop shaft pulling out with the pin and set screws, and a key, but the shaft and coupling should be within .0005 MAX and it should be a tight fit! I've installed quite a few properly machined shafts & couplings over the years and none of them had any wiggle coming from the shafting shop and every one, especially the larger ones on commercial boats, required some form of rubber mallet or wood blocks to drive them into the set screw divots though most shafts over 1.5" generally use a split coupling so it's a non issue but occasionally they do use a solid.

You could have purchased a brand new solid coupling for $55.00 and had it fitted and faced for less than you had one built for.

Solid Coupling (LINK)

You could have also purchased a split coupling for only $74.00!

Yanmar 4" Split Coupling (LINK)

P.S. I don't see a key in that shaft? I hope there is one even with the pin. I can't tell you how many "shear Pins" I've sheared over the years on various equipment. Boats use shaft keys for a reason.

I know you think we're all a little "dumb"

in the marine world, compared to the engineering field, but please do add a key if you don't have one. Keys are not added for looks. If a simple pin worked that's what would be there.

Even "splits" have keys:

Bob S · Nov 12, 2008

Mainesail,

Is there a reason why these are made of ductile iron. Wouldn't 304304L or 316/316L be better? Is it just a cost thing?

I agree with the key. If was going to pin them I would have used a dutchman where you drill the hole horizontal through the shaft and coupling then pin it. It's kind of like a round key. Not a good fix because it''s near impossible to remove.

Bob

Hermit Scott · Nov 12, 2008

wiggle

Not that kind of wiggle, that's called slop not tolerance. The wiggle I am talking about it twisting it back and forth, like the action of threading and unthreading a bolt. You can't just slide the coupling on. The tolerance is under .001 and maybe .0005(I don't have an instument to measure in hundred thousands, it fits so well I don't care) but you don't have to hammer this one on. The guy that made it primarily makes parts for aircraft retrofits. Even at a FIT of .0005 you should be able to slide the coupling on provided the keyway has been chamfered and it is very clean. Having to hammer something on denotes a press fit or a keyway that is not properly cleaned.
After dealing with the shaft I took out of this boat, and seeing what happens after a shaft has been in a boat just a few years, the shear key isn't worth anything in the coupling.
Maybe the shear key in the prop would still shear at it's rated torque but on the coupling/shaft end I took out of my boat, you could have taken the shear pin out (had it been possible) and still not spun the shaft at the shear pins rated shear torque. 10 tons crushed the coupling and still didn't move the shaft in there. I gave up trying to get it out at that point, and decided I would do something different.
Are these shear pins? Like a woodruff key? They extend the length of the shaft, they act more like a spline than shear point, and once the shaft and coupling are fused together they might as well be welded together.
Every price I checked on a split coupling was $95 or more. I would rather use stainless though instead of something that's going to rust and degrade so quickly.

Mainesail, when you say they are machine to fit with in .0005" What is the tolerance specs?
There has to be a +/- to the tolerance of the coupling AND the shaft it fits on.
The coupling I have made was made for the shaft I have. That's why it fits perfectly.

Hermit Scott · Nov 12, 2008

what

Why would you say I think you are dumb? Just because I question how or why things are done doesn't mean I think you or anyone else is stupid. I ask questions to cure MY ignorance not reveal yours. I don't want to just know how to do things right, I want to know why. If I thought you were stupid or ignorant why would I ask you how things are done? The only one on here that ever pisses me off is saildog, but I still respect him and his knowledge.

Anyway I think they use keys in line with the shaft becasue even if they are partially sheared they can be hammered off. If you have a pin through and through if it's partially sheared, you have to shear it the rest of the way to get it off. I am going to use a hardened pin that won't deform. It won't budge or it will shear through. Either way I should be able to remove it.
I do agree that a key would be best because of that. We put a key way for t he prop, but he didn't have a way to put a keyway inside the coupling. I didn't know that until the end of the job. If I have a problem with a pin, I can always pull it out and put a keyway in. I just don't want to install another steel coupling and have it rust away again.

Ross · Nov 12, 2008

Re: what

When I worked in the trade we detailed "fits as sliding, press and interference". A sliding fit was very smooth and close and oil was helpful. A press fit could not be assembled by hand but there was a small difference between shaft diameter and hole diameter, an interference fit held that the hole and the shaft had to deform elastically to be assembled. It was just a little tighter than a press fit. Then there was a shrink fit, where in the flange was heated to a dull red and forced onto the shaft before it cooled. A shrink fit was practically impossible to remove with out damaging one or the other pieces.

Maine Sail · Nov 12, 2008

Hermit

Sorry about the "dumb" comment it was meant to have a winkie

next to it,meaning "kidding", but it was early when I typed that and apparently forgot it..

Hermit Scott · Nov 12, 2008

Alot gets lost when typed.

Shaft Coupler

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