Change a Dripless Shaft Seal while in the Water?

[Statistical]

Originally Posted by rgleason

Thank you Statistical for your answer. Do you have any idea how long the thinner and more fragile bellows fails and what causes the failure generally?


How likely is it that the bellows would last 10 years? The information PSS has states 6 years maximum which would be a PITA to change that frequently.

Could it last 10 years? Sure. I wouldn't be going beyond six (personally I don't go beyond four). It is easiest done on a haul out and I assume you will haul out at least once every four years.

If installed properly and you have reasonably good shaft alignment and you replace them as dictated they are pretty much maintenance free.

As for what fails the most I am too much of a coward to find out but I inspected the rotor & stator when replacing the bellows a couple years ago and it looked essentially brand new. So if I had to guess most failures involve the bellows cracking/splitting or starting to leak at either the it is the bellows that fail the most. They get old and eventually crack or start leaking past the clamps.

[skipperpete]

Originally Posted by rgleason

Thank you Statistical for your answer. Do you have any idea how long the thinner and more fragile bellows fails and what causes the failure generally?


How likely is it that the bellows would last 10 years? The information PSS has states 6 years maximum which would be a PITA to change that frequently.

Most of the PSS problems I encounter seem to be human related, not product fragility. It can be as simple as an overly compressed bellows or far more likely, inexpert attempts to move the propshaft back to check engine alignment or replace/service parts of the drive line attached to the engine. I’ve seen cases of the shaft being forced back with levers to open the coupling without releasing the stainless steel annulus, also seen where guys have hammered that stainless steel ring or destroyed its orings by sliding the ring along a scarred and damaged propshaft. And then there’s the alignment issue, a PSS will tolerate a degree of engine mis alignment that a conventional stuffing box would not , so the bellows takes a set to accommodate the poor lineup. Last but by no means least there’s a high damage level caused by the tendency of the sealing faces to adhere to each other, often after a long dry out on the hardstand but occasionally from a hardened salty crust if the shaft hasn’t been turned for a few months…. An older bellows can tear if this isn't addressed before popping er into gear and backing out of the berth or slings. Not everyone knows about burping dripless or lipseals, many do not have a vent line.
When PSS seals are well installed they provide fairly reliable operation for many years but, rgleason you’re right about some dripless seals being less robust than others and not as reliable as the ancient stuffing box….just much drier.

[rgleason]

skipperpete

Thanks very much that helps. This one I was unaware of:

"Last but by no means least there’s a high damage level caused by the tendency of the sealing faces to adhere to each other, often after a long dry out on the hardstand but occasionally from a hardened salty crust if the shaft hasn’t been turned for a few months…. An older bellows can tear..."

I am running a air vent up to the deck.

The prop service company has checked the prop balance, the shaft wear and straightness, checked and adjusted the fit of the prop and the flange, machined the flange a little.

They said that they have PSS shafts 10 years quite often. To carefully inspect and check the bellows every year before launch. So I purchased one!

[s/v Jedi]

So here is the outlier: my PSS bellows are in perfect condition at a minimum of 22 years old, possibly 30 years old.

I believe this is because:

- a perfect alignment that never changes because the shaft terminates at a thrust bearing (AquaDrive) so also no shaft movement other than rotation.

- a permanent vent line up into the cockpit footwell

- a thorough check before every launch, especially if the shaft turns freely. This really is automatic when one greases a MaxProp, but I add a visual inspection of the shaft seal while turning it by hand. I did have sticking surfaces once and can see how this could damage the bellows

- I hardly use the engine, we are a sailboat. With the MaxProp feathered, there is no rotation during sailing either.

I must admit that I had expected degradation of the rubber that the bellows is made from but it really is like new. No hardening at all.

I have a complete spare PSS seal aboard but it is at least 22 years old as well so I will buy a fresh spare bellows to compare against, but I have a feeling the old ones may have better quality rubber?

[GILow]

Originally Posted by s/v Jedi

… but I have a feeling the old ones may have better quality rubber?

Somewhere back in time there was a bad batch of PSS seals where the rubber lost its resilliemce and basically collapsed away from the ring. I feel like this was around ten years ago. A search of this forum may track down the dates perhaps. But I reckon the manufacturer may have learned from that episode.

[carstenb]

So, we are now in Shelter Bay and my (2) new spare shaft seals have just arrived. So if it happens again, I have a spare. I hope not. As Jedi said, we are a sailboat. But we had to motor a lot coming down the west coast of Central America.

It was just like the Med, either way too much wind or no wind at all.

Thanks for the comments - hope none you have to try this yourselves