PSS shaft seal adjustment

[Johnny D]

My PSS shaft seal was leaking while under way so I tried to adjust the collar. I removed the set screws and pushed the collar into the carbon surface and bellows. The collar move about a 1/2 inch and stopped. I thought the collar was stuck, but when I checked further I found it was the carbon and bellows that would not move any more. The spec for the compressed length for a 1 inch shaft is 6.21 inches. I am only able to compress the total seal 6.75 inches. Any ideas?

[markxengineerin]

Can you slide the collar the other way enough so that you could reach inside the bellows and see if there's some debris in there, or other reason why it won't compress? I have one on the bench that I'll measure and take pics of later today for reference.

Also try inspecting the sealing surface on both the collar and the carbon ring. If it looks messed up, that is probably the cause of a leak more-so than the exact compression length and pressure. This is my opinion based on other face seal applications; I have never experimented with different spring rates on this one.

[markxengineerin]

I can't get mine (for 1" shaft) to compress more than half an inch, on the bench, from its natural position. Its natural position may be shorter now vs. when it was new.



Thinking more about it, i doubt your issue is debris- whatever is in there would have to come through the tight clearances of the cutlass bearing.

[Johnny D]

My seal length is 7 inches uncompressed. I got it to compress to 6 3/4 inch. You say yours is very hard to compress on the bench, maybe I didn't try hard enough to compress it.

[Johnny D]

That 7 inches is the collar and carbon and bellows combined. The carbon and bellows is 6 inches.

[mikereed100]

How old is your PSS Shaftseal? They do lose compliance as they age. Manufacturer recommends replacement at 6 years.

[HeywoodJ]

Any chance the bellows is installed way down the stern tube so that the stern tube is inside the bellows and when you slide aft the carbon block is hitting the end of the stern tube? You might be able to tell that by feel or by loosening the hose clamps and seeing if you can compress the bellows by sliding that end forward (although that could be a bit scary in the water).

[GreenWave]

The surface mate between the carbon seal and the stainless flange needs to be clean. The way to do this is lightly sand the carbon flange. Also not recommended to reuse the set screws. A refurb kit can be purchased online.

[osprey877]

I had the same issue with my shaft seal. I phoned PYI and sent them photos of the black spray it was emitting. They responded right away and said I should first wet sand the face between the carbon rotor and the stainless one with 600 grit paper, then retention the bellows. I also found it very hard to properly tension the bellows with boat in the water but was able to do so by securing a hose clamp to the shaft just in front of the stainless rotor and then using a thin screwdriver as a lever to pry the stainless rotor back down the shaft. If you can’t get enough movement in one go, then temporarily tighten the set screws so you can reset the hose clamp closer for a second go. I just adjusted mine last week so haven’t had much of a chance to test, but seems to be an improvement. Pyi said the carbon and stainless rotors should basically last forever, but the bellows need replacing every 6 or 7 years.
I found trying to insert sandpaper between the rotors was next to impossible in the water, so I made a jig by glueing the sandpaper to an 1/8th inch plywood jig as per photo below. Force it between the rotors, then turn the shaft by hand. The sandpaper jig needs to rotate around the shaft in order to polish the carbon rotor. Hold it form to polish the stainless side.
I also attached a photo showing the pre repair spray. You will see I leave the hose clamp in place as a backup to the set screws and put a piece of tape just behind it so I can easily check if there is any slippage. Good luck😊

[Orion Jim]

If I recall correctly there are four set screws. They are doubled up, in effect set screws for the set screws. If all four were not removed you may not get the full travel during compression.
As mentioned earlier the bellows is due for replacement after six years. I’m replacing mine in a couple weeks.

[Johnny D]

The shaft seal is 2 years and 10 months old. Heywoodj I was thinking the same thing about the bellows being pushed to far on the shaft tube. Checking that while the boat is still in the water could be tricky.

[vanderd]

There are 2 set screws in each hole. The second prevents the one against the shaft from loosening up. Also the set screws have a special tip to dig into the shaft and they are NEVER to be reused. Their failures which could be catastrophic are generally because the set screws were reused.

[markxengineerin]

Tiny stainless set screws are the devil- damn things are always getting lost (magnet won't pick them up) and/or stripping out, especially when bad quality allen keys, salt water, loctite, and cramped boat access are involved. I have modified my stainless collar ring to accept the next size up thread (careful to not go full depth and enter o ring grooves). This provides more clamping force, less chance to strip. I might also go with a normal bolt instead of a set screw, as I don't see any disadvantage. It's not like the shaft is spinning fast enough for balance to matter- better to worry about the barnacles on the prop.

Has anyone re-used the set screws? I would bet they don't fall out.
Are marine prop shafts usually hardened?

[Jim Cate]

Has anyone re-used the set screws? I would bet they don't fall out.
Are marine prop shafts usually hardened?

The stipulated reason for not re-using the screws is that the pointed tip gets flattened and does not engage the shaft as well as a new one does.

And no, never I've never heard of a yacht sized shaft being hardened. Many are made of materials that do not harden readily, too, like 300 series s/s and bronze.

I wonder if one could reasonably use one of the square-headed set screws often seen on shaft couplers... complete with holes in the head for safety wire.

Jim

[osprey877]

Originally Posted by markxengineerin

Tiny stainless set screws are the devil- damn things are always getting lost (magnet won't pick them up) and/or stripping out, especially when bad quality allen keys, salt water, loctite, and cramped boat access are involved. I have modified my stainless collar ring to accept the next size up thread (careful to not go full depth and enter o ring grooves). This provides more clamping force, less chance to strip. I might also go with a normal bolt instead of a set screw, as I don't see any disadvantage. It's not like the shaft is spinning fast enough for balance to matter- better to worry about the barnacles on the prop.

Has anyone re-used the set screws? I would bet they don't fall out.
Are marine prop shafts usually hardened?

The set screws can’t be reused because once you cinch them down the sharp dimple at the end of the screw is compressed and won’t grab the shaft if you try to use them a second time. However, you can swap the order of the set screws in each hole if you haven’t used the back up one. Ie put the outer set screw in first, then backup with the used one.
It’s easy to see by looking at the end of the set screw whether or not they’ve been used. When removing/tightening them, they take a 1/8” SAE Allen key, NOT a metric key. You can back up the set screws with a couple of hose clamps around the prop shaft immediately upstream of the stainless collar. This will prevent it slipping up the shaft under pressure from the bellows. However, the stainless rotor has to rotate with the prop shaft against the stationary carbon rotor and the only way to ensure this happens is to use new set screws when you put it back together. PYI have a number of videos and their email/phone support was excellent on the few occasions I’ve had to contact them.