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Old 20-04-2013, 12:27   #1
F51
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PSS Shedding Carbon

My PSS shaft seal is shedding carbon powder--slowly, I think. Is that normal? It certainly surprised me to find it. The seal is still working but I just wonder for how long? What would cause the carbon loss?
Thanks.
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Old 20-04-2013, 12:30   #2
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Re: PSS shedding carbon

This not not normal. First thing to check is if there is water reaching the mating pieces.
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Old 20-04-2013, 12:32   #3
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Re: PSS shedding carbon

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Originally Posted by F51 View Post
My PSS shaft seal is shedding carbon powder--slowly, I think. Is that normal? It certainly surprised me to find it. The seal is still working but I just wonder for how long? What would cause the carbon loss?
Thanks.
I'd check how tightly the stainless doughnut is cinched up against the carbon. Sounds like it might be a bit tight. You want some pressure, but not much as the system relies on a film of water for lubrication of the steel against the carbon. Mine hasn't show any signs like that in six years.
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Old 20-04-2013, 13:50   #4
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Re: PSS Shedding Carbon

I would be checking the water availability to the mating surfaces. Usually a hose is run from the PSS to well above the waterline, to allow air to escape and water to flow to the mating surfaces. With larger engines some exhaust raw cooling water is pumped through the hose into the PSS and out the stern tube. IIRC some (low power) installations don't have a hose barb on the PSS; in this case after launching the boat the mating surfaces must be pulled apart for a few seconds to allow the air trapped in the tube to escape. [Edit: it may be necessary to do this with the forced water flow as well.] Failure to eliminate the air would cause excessive wear. The PSS manual provides guidelines for the choices above.

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Old 20-04-2013, 13:56   #5
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Re: PSS Shedding Carbon

mine shed packing when overstuffed. try that bit first. looks like carbon.
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Old 20-04-2013, 13:58   #6
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Re: PSS Shedding Carbon

If you do not have the new "venting" version of the PSS shaft seal then you will need to "burp" the seal occasionally and especially if the boat has been taken out of the water, then put back in.
Also sometimes after long periods when you have not used the boat - "burping" the seal to release any air and re-wet the seal surface is a good idea.
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Old 20-04-2013, 17:09   #7
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One boat I sailed on needed the unvented PSS burped every time we started the engine after sailing fast. Maybe it was air bubbles trapped under the hull that somehow got into the PSS. It should have had a vent. She also got air into the engine raw water filter so we had to remember to bleed that as well or the raw water pump wouldn't prime.
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Old 20-04-2013, 21:09   #8
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Re: PSS Shedding Carbon

If you have a non-venting PSS seal, then it is old enough to need replacement.

Too much compression or a dry (air bubble) rub will ruin the seal.

Call PYI and they can set you up with a replacement part.
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Old 21-04-2013, 00:27   #9
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Re: PSS Shedding Carbon

And one more possibility! I've noticed if a PSS has set for a long time w/o use, a little bit of corrosion starts between the surface of the SS and the carbon. If so the rough surface could be tearing away at the carbon.

I had one that sat for 9 months and found pitting in the SS seal. So I machined about .005" from the face and it was like new again.

But yeah, I would check for air in the PSS. All the new ones come with the vent/water fitting now.
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Old 13-05-2013, 13:55   #10
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Re: PSS Shedding Carbon

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If you have a non-venting PSS seal, then it is old enough to need replacement.
mine is almost 10 years old. Its been out the last two winters and everything looks very good. No cracking on the rubber, carbon and stainles mating surface is very smooth, no leaks. In fact rubber looks brand new, like i just purchased it. Should i be watching gout for specific signs of wear?
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