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Old 11-29-2022, 04:25 PM   #1
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Shaft Seal Bellows

I got a new shaft seal bellows installed in 2017 when the boat was finally commissioned.

Now I have a steady drip.

I removed the two clamps at the suspect end one at a time and reinstalled making sure they were on tightly.

I think this is the only below waterline "rubber hose" connection I have that does not have a shut off valve. So I am a little sensitive about leaks at this area.

Is there a magic wand or is the bellows at the end of its design life?
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Old 11-29-2022, 04:53 PM   #2
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Do you know what brand the shaft log is?
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Old 11-29-2022, 05:12 PM   #3
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Dave,

Not really, the bill says "Fiberglass log tubing"

The shaft log problem was discovered during the second attempt to launch. I have some nice pictures of the old pinholed stern tube and the special tool made to ream it out for the new fiberglass tube. But no info on manufacturer.

John
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Old 11-29-2022, 05:15 PM   #4
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Pictures might help. When I saw "Bellows" I assumed it was a dripless system such as PYI, but now I'm not so sure ('pinholed stern tube?" What is that?).

Peter
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Old 11-29-2022, 05:46 PM   #5
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It sounds like the shaft tube, fiberglass, was replaced. But the bellows should be part of the shaft log, dripless or traditional. Agree some photos would be a big help in figuring it out.
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Old 11-29-2022, 06:18 PM   #6
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The leak isn't likely to be from the clamps being loose. It is more likely to be at the interface of the static and rotating components.

If these are conventional seals, that is between the packing in the stuffing box and the shaft. In a boat that new, it'd likely be cured by slightly tightening the stuffing box. Having said that, since you mention bellows, I don't think you have this design.

If you've got a dripless shaft seal, it could also be a lip seal, where there is a static ring with lip(s) that seal against the shaft. This ring can wear out, in which case it needs to be replaced. Sometimes a spare is left on the shaft for this purpose and can be moved into position without the need to disconnect the shaft. These can also eventually wear into the shaft, requiring adjustments to move them up or down the shaft a bit to get a new, fresh part of the shaft to seal against. But, since you are mentioning bellows, I don't think you have this kind, either.

I suspect you're configuration uses a face seal. Perhaps you have one of the models from PSS. A stainless steel or ceramic ring called a rotor is slipped onto and attached around the shaft and spins with it. A carbon disc, called a stator is fixed to one end of a rubber boot, the bellows, which is fastened at the other end to the log, the fiberglass tube around the shaft before it is exposed. The seal works by having the face of the rotor spin against with the shaft against the face of the stator. THe interface between the two is not intended to leak. This interface is often cooled by water-flow through the bellows via a vent line. The seal relies upon both the rotor and stator having very smooth, very clean surfaces at the interface and the bellows being compressed enough to provide the correct amount of pressure for a good seal, but not enough to generate excessive friction and heat.

Leaks at this interface can often be addressed by ensuring the mating surfaces are smooth and clean and that the bellows are applying the right amount of pressure. If the faces at the interface are smooth and clean, one can loosen the hose clamp(s) at the other side of the bellows and slide it a little bit closer to the interface, compressing the bellows a bit more, and then retighten the hose clamp in that position. This will apply more pressure to help seal the interface. It normally takes very little adjustment to properly adjust things, maybe 1/8" or 1/4".

If it takes more than that, there is probably something else going on, maybe a defect in one of the two mating surfaces or the bellows are becoming less spring-like with age. If the interface gets hot, the rotor or stator can warp, which will prevent a good seal. In the extreme, the stator could even crack. If the interface is allowed to remain dirty, it can damage the face of the rotor or stator, requiring the replacement of the stator and/or the cleaning up of the stator on a lathe.

I'd start by inspecting the interface between the static and rotating components of whatever system you've got.

If you can post pictures, I'll be someone here will recognize it and someone here will have some more specific advice.
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Old 11-29-2022, 09:27 PM   #7
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Thanks for all the feedback. Iím in the middle of heading back north for Xmas, but will try to get a photo before I leave and post it as soon as I can.
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Old 12-01-2022, 03:02 PM   #8
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PMF,
Yes, some photos as well as more detailed info regarding the "pinhole leaks" and new "shaft tube" issue?

It is possible that the rubber bellows is not leaking, but it is coming from nearby???
STB (above) gave a good description of the PYI/PSS "dripless" seal and the adjustments that can be made. The rubber bellows of that system has a definite "life" expectancy (approx. 6 years for the older model and 10 years for the "upgraded" version), due to the requirement for the bellows being able to maintain the necessary compression (pressure) on the mating surfaces. This life could be shortened by exposure to any number of contaminates, or it could be inadvertently damaged (cut) causing a leak. At lower speeds (rpm's) a supply of cooling water from the engine is not needed, but for most "planing" applications this cooling water is essential.

Hopefully you can supply more info and photos, and maybe someone here can help?? Good luck.
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Old 12-01-2022, 04:07 PM   #9
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There is another often overlooked issue with the PYI type dripless. If the boat is left idle for any period of time in salt water, the two sealing surfaces can stick together. The first time you put it in gear they tear apart with a jerk. It does none of the components any good. You are supposed to move the bellows by hand to unstick it after a layup.
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Old 12-01-2022, 04:15 PM   #10
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Quote:
Originally Posted by DDW View Post
You are supposed to move the bellows by hand to unstick it after a layup.
Even clean DSSs need to be burped after being on the hard to get the air out so that water can cool the stator and to make sure everything is aligned and stays aligned.
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Old 12-01-2022, 05:28 PM   #11
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Folks,

Thanks for the detailed replies. (although some of them are over my head)
The photo is below.

FYI the boat did sit from early June until late October without the shaft turning due to my job demands.

John
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IMG_0107.jpg  
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Old 12-01-2022, 05:38 PM   #12
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Also, with a PSS style dripless system like I have you can look for the "Dreaded Black Line", which would indicate you are leaking from the face of the carbon seal where it presses against the shaft mounted ring and the resultant black spray is staining your bilge. I had that lovely situation last year.
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Old 12-01-2022, 07:07 PM   #13
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John,
Yes that sure looks like a PYI/PSS dripless shaft seal. From the photo, it looks to me that you MAY be leaking where the cooling hose attaches to the black (carbon) disc. The clamp looks rusty, so that should be replaced for sure. Possibly either, or both of the hose itself or the black disc (fault probably with the hose barb) may also need replacing.
As others have said, burping after a long haulout may be required.
See the company website for lots of info: https://www.shaftseal.com/pss-faq.html
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Old 12-01-2022, 07:53 PM   #14
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Yeah. That is almost certainly a PYI. See my note above about the face seal style.

The hose clamp on the vent line does look super rusty and there seems to be some rust on the clamps on the log (fiberglass pipe) side. I'd replace all three without delay.

With luck, that will fix it. It could just be the connection of tha5 vent line to stator leaking while underway.

But, it could also be that the rotor-stator interface is leaking underway and, with the rotor (stainless steel hockey puck) spinning with the shaft, throwing water around and causing the clamp(s) to rust. You'll have to try and see. If, and only if, that is the case, just loosen the hose clamps on the log side of the bellows and push that end of the bellows to compress it a little more against the rotor and reclamp it. The extra pressure will help the seal. Maybe 1/8" to 1/4". Also, before doing that, just to be sure, pull that stator back away from the rotor (water will come in) and feel the face of each of the rotor and stator just to make sure they are smooth and clean.

Good luck!

And, maybe that is the only issue. But, I'm betting that is is spraying from the interface between the rotor and stator while underway that has rusted it.
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Old 12-01-2022, 07:56 PM   #15
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Tom,

Thanks for the link. Thatís just what I needed as it explained with pictures what I have, how it works, what can go wrong, and how to fix it.

As to the hose clamps, I took them off and cleaned them up a bit , also noted size so I can order new ones.

Thanks for all the help guys.

Iím away from the boat for a month ( I do have some one to check on it every few days) so I will not be reporting on the cure until then.

Have a happy holiday season.
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Old 12-01-2022, 09:26 PM   #16
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I would replace all 5 clamps with some 316 S/S clamps like AWAB or ABA brands. Also check the bellows carefully for any signs of cracks or the beginning of cracks.
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Old 12-01-2022, 10:19 PM   #17
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These bellows are stoutly built. From memory, PSS recommends 5-7 year. In practice, many people see well in excess of 10 years. How difficult is it to compress the bellows? If the compress easily, thr collar may have shifted (though the picture looks like bellows are fairly well compressed). It's possible to move the collor aft and further compress the bellows - note that the set screws are doubled-up: there is an outer set screw that presses into an inner set screw.

If the injection hose is the culprit, it will leak more when you're running than at rest.

If the leak is between the two faces, you will be able to feel the wetness and trace back that it is dry aftward.

How much water is accumulating? How often do you run the boat? Where are you located and do you have silty water? You have a very narrow bilge beneath the fitting. But might be able to put something underneath such as a butter dish to see where the leak drips.

I really doubt its the bellows at 6 years. It's more likely one of the hose clamp connections, or the sealing surface.

Good luck. Sounds frustrating.

Peter
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Old 12-02-2022, 02:41 PM   #18
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Side note: Add a hose clamp, or shaft type clamp that butt's up to the collar. Those set screws are notorious for sliding down the shaft due to the bellows pressure on the collar. I had this happen to me crossing the Straight of Juan de Fuca. Very exciting indeed!
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Old 12-05-2022, 01:44 PM   #19
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the pyi "dripless system". a whole new set of problems from a "solution" to a problem that hardly existed.
they should sell a kit to take you back to a regular stuffing box with some goretex stuffing.
a lot safer and a heck of a lot cheaper than replacing the pyi every 6 -10 years.

i just replaced my PYI in my Mainship 30. very tight quarters and an expensive process.
I also some years ago had a Sabre 42 that in its previous owner billings had an invoice for emergency haulout due to dripless bellows leak.
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Old 12-05-2022, 02:38 PM   #20
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Face seals like this are sensitive to a few things that can cause leaks.

Excess vibration of the shaft or engine

Over and under compression of the bellows.

A injection hose that isn't flexible enough and or one that is side loading the stator.

If the shaft is not centered in and parallel with the shaft log.

The injection hose is a common culprit and yours looks as if there is no slack. It has to allow the stator to float. The hose should be very flexible, Type B fuel hose or blue silicone (like the hose shown in the opening photo of the article) hose.

More here https://stevedmarineconsulting.com/k...tuffing-boxes/

More here
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