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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 02-25-2008
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PSS shaft seal

The PO of my Heritage 1 Ton replaced the stuffing box with a PSS shaft seal. I'm looking to rebuild my transmission (old MS on a Volvo MD2B), and need to move the prop shaft back to pull the transmission. I'd like to do the work on the mooring rather than take the boat over the St Thomas to haul out.

The voices in my head keep saying "rob a bank, make the trip, haul out, do the tranny job, replace the PSS seal (around 5 years old), check the shaft for wear, check out the prop, and replace the cutlass bearing while you're at it".

The voice in my wallet keeps saying "figure out a way to fix the tranny at the mooring so you've got a functional auxillery, then make the trip to haul out and do the other work when you can better afford it. You're already committed to rewiring the entire #&*!% boat!".

Has anyone had experience with removing / replacing a PSS Shaft seal in the water? On a related note, has anyone set up a "spare" seal boot on their prop shaft as a precaution in the event of a shaft seal failure?
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Old 02-25-2008
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The one downfall of the PSS seal is the fact that if you disturb the engine/tranny position you open the seal.

We pulled the engine on our boat with a PSS seal, and of course once the compression of the bellows tube was released the seal wanted to leak a lot. We got around it by securely taping the shaft collar to the stern-tube half with water resistant tape.

You really can't remove the seal without decpoupling the shaft, and you can't pull the shaft without removing the seal, neither is an in-the-water job.
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Old 02-25-2008
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A fellow on the C-34 website described doing the job with the boat in the water. My recollection was the he uncoupled the shaft from the transmission. Slid the shaft back enough to remove the coupler and then he dove under his boat and packed clay or plumbers putty around the shaft and shaft tube to slow down the leak when it was time to actually replace the PSS seal. Sounds scarey to me, but might work.
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Old 02-25-2008
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The short answer is Yes

You can ..The PSS uses tension of the bellows against the mating surface wear plate which is held to the shaft by set screws..I dont know about your tranny but my Hurth needs about 3" clearance to pull free..It is possible to loosen the set screws slide back the shaft,,secure it with whatever means you can and reposition the wear plate and re tighten the set screws in place..with minimal water intrusion...HOWEVER

This is one of thoes few Job where I would want to watch a mechanic do it the first time so its all on his nickel if you know what I mean...

I will be doing my tranny before it goes back in the water this spring...OK call me chicken...

Edit:

For thoes unfamiliar with the PSS upon haul out you stern tub will drain,,so when relaunching air will be trapped it the tube and it is necessary to bleed this out so water can lubricate your seal...all thats needed to accomplish this is grab the bellows with both hands and pull hard parting the two mating services till water pours in...let go ...make sure its mated and not leaking and your done..
If there is a little seepage ..it will go away as soon as you fire up your engine and spin your shaft a few times...

Last edited by Stillraining; 02-25-2008 at 02:42 PM.
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Old 02-25-2008
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PSS Bellows 6 year interval

I'd be careful on this one! The PSS shaft seal is a mechanical seal, and mechanical seals, wonderful as they are, can be touchy - if you damage the very brittle "stationary" face at the FWD end of the bellows, you will be changing it out - no choice! This obviously cannot be done without either withdrawing the prop shaft or removing the drive coupling and sliding the whole works off the FWD end of the shaft - not something I'd do in the water!

Also, PSS recommends replacing the rubber bellows every 6 years (it's true - check out their literature), so yours is about due anyway. Two reasons for this: first, the axial pressure on the seal faces is dependent on the "spring" in the rubber bellows - this decreases over time; and second, all rubber products continue to "cure" over time, so brittleness and resultant cracks will ultimately develop. Will it fail in 7 years? Maybe not, but I wouldn't chance it.
Good luck!
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Old 02-26-2008
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I have replaced my shaft seal in the water on my KP44. It does have two Cutless bearings so water intrusion is not too bad. I turned to rudder hard over, decoupled the shaft, and worked it back to allow the PSS to be slipped on. This might not work on your boat. I have had no problems with the PSS in 9 years but I intend to change out the bellows this month.
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Old 02-26-2008
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Oh yes, very important. YOU MUST USE NEW SET SCREWS each time you move the shaft collar.
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Old 03-01-2008
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Thanks for responses and advice folks. Looks like I'll be hauling out to deal with the shaft seal, etc. Well, I'm off to start casing some banks...
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Old 03-02-2008
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You can certainly get the transmission off if you move the shaft back a little. Beware that the big thin spacers do not fall into the bilge though. They did with me, on the olde MD17c. Any old chart paper will serve you well for the gasket. Just tap round it with a wee toffee hammer.

I know nothing of that shaft seal.
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Old 04-06-2008
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I'm at the decision point

now the rudder is dropped, the shaft and cutless bearing are out also.
but I'm still undecided on getting the PSS. $200 for the pss is not all that much for a onetime deal, but on the other hand a stuffing box is way less then a $100. for a 1" shaft. Anyone want to comment on the PSS? The old seal was a "strongseal" that was worn badly. I didn't like it, trashed it.
thanks all
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