PSS shaft seal

[STOL71]

Mv sailboat has a PSS non-drip shaft seal. On high revs (3000RPM+) I have some water splurting in when the shaft is pushed in forward gear. There is no water coming in on revs below 3000 rpm or when not in gear. The amount of water coming in isn't enough to be alarming, plus rarely that tI run the engine at 3000+ rpm.

I suspect that the bellow doesn't have enough tension and planning on changing the bellow at the end of the season when I haul the boat out.

Meanwhile, I would like to increase tension on the bellow by moving the stainless steel rotor back by a few millimetres. Was planning on undoing the set screws after clamping the rotor in place, move the rotor and use new set screws to hold the rotor at its new position few millimetres back.

My question: I am planning on doing that whilst the boat is in the water. Is that too risky? Anyone has experience in doing the above with a PSS seal?

 

[superheat6k]

This is straightforward, but put a jubilee clip on first next to the rotor, so it can't slip back when the grub screws are released. Be aware there are two grub screws in each threaded hole, the first has to be fully withdrawn to access the inner, and PSS recommend they are not re-used.

When I fitted the PSS seal I used an extended 10mm nut with a piece of studding to jack the rotor collar forward agains the tension of the bellows and against the output coupling.

https://www.ebay.co.uk/itm/Hex-Stud...hash=item1c9df1c1fb:m:m0MIXGZnbPJrA95hXNhTMZA

 

[emmalina]

Every shaft has a frequency where it resonates. Sounds like yours does at 3k rpm .Increasing bellows pressure won't stop it just put more strain on the bellows. If you modified an old packing gland to a PSS this would explain it. Had a similar problem on a boat and after years of trying we retuned to a packing gland !

 

[Daverw]

Has said, just move it backwards and add I bit more tension, in forward gear as the revs go higher the shaft is forced towards the engine and takes tension off the bellows.

 

[zoidberg]

'Superheat6k' has it spot on.

After a near-sinking following a failure of the PSS seal setup ( and multiple others discovered ) I won't sail with one that doesn't have a 'failsafe' Jubilee clip or two preventing the rotor component from sliding forward and letting the ocean in. The grubscrew arrangement is inadequate.

It's a cheap and easy fix. It's what the PSS people insist on for all their commercial products. Why they haven't responded to the many 'failures in service' of their yottie product demands an explanation.

In case you're wondering, I have very good reason to be emphatic!

 

[Topcat47]

High revs equates to higher thrust from the screw. If you engine mountings are a bit soft, you'll get this effect, too. Yanmar Mountings tend to be soft anyway so a little more pre-load o the bellows is never a bad idea. +1 on the jubilee clips. I have two back to back on my shaft and I don't take them off after setting up the collar, just slide them up to it after squeezing up the bellows.

 

[doug748]

......My question: I am planning on doing that whilst the boat is in the water. Is that too risky? Anyone has experience in doing the above with a PSS seal?

As others have said not risky at all, though a bit of water will spout.

On the smaller units the compression is 3/4in (I think) which is quite a bit. The installer may have reneged on this or it may have slipped a bit I would wiggle it back till there is little tension and then give it the full three quarter - you may find that solves the problem. It can help to push a jubilee clip up behind the rotor tighten it up and then use it to lever against with a screwdriver, to get the required compression. An added refinement is a 3/4in block of wood to use as a gauge before you nip up the allen screws. I have always kept the jubilee clip at 3/4 from the rotor so I can see if it slips, it never has. The allen screws seem soft and have never marked my propshaft, I guess they are designed that way. I must confess I have reused them but not before re-fettling the points with a suitable drill.

I had the spraying problem once when my engine went out of alignment due to a nut coming loose on an engine foot, might be worth a check.

I changed my bellows this winter, beware new ones are over a hundred quid! The old was exactly the same length as the new, after ten years.

 

[STOL71]

When I fitted the PSS seal I used an extended 10mm nut with a piece of studding to jack the rotor collar forward agains the tension of the bellows and against the output coupling.

https://www.ebay.co.uk/itm/Hex-Stud...hash=item1c9df1c1fb:m:m0MIXGZnbPJrA95hXNhTMZA

I don't understand this bit.
Thanks for everyones input.
Very helpful.

 

[STOL71]

Is it a normal hexagon allen key for the set screws? I've got spare set screws on the boat but cannot remember if they came with a special key.

 

[Daverw]

I don't understand this bit.
Thanks for everyones input.
Very helpful.

I think he means to use the stud as a adjustable spacer to keep the compression on the bellows as it’s pushed to compress

 

[STOL71]

Yes, understand. My propshaft is rather long , won't be able to use anything against th coupling.

 

[superheat6k]

I don't understand this bit.
Thanks for everyones input.
Very helpful.

Cut a piece of studding so it just fits between the rotor and coupling, apply two normal nuts at one end and lock these together. Run the long nut fully onto the other end, then hold the stud bar between the two surfaces of the rotor and coupling and using two spanners unwind the stud from the long nut, thus forcing the rotor into tension against the bellows. This will give you ~15mm of movement of the rotor toward the bellows, but if you then need more use a spacer block for extra distance, although I would expect 15mm would likely be sufficient.

This method worked for me, and made tensioning the seal very simple. The jubilee clip provides a reference point to check how far the rotor has moved.

 

[superheat6k]

Yes, understand. My propshaft is rather long , won't be able to use anything against th coupling.

A stiff angle bracket held onto the shaft with another jubilee clip will give you a firm surface to push against. I would weld a nut or tap a suitable thread onto said bracket that the stud can wind out of instead of the long nut

 

[mbroom]

'Superheat6k' has it spot on.

After a near-sinking following a failure of the PSS seal setup ( and multiple others discovered ) I won't sail with one that doesn't have a 'failsafe' Jubilee clip or two preventing the rotor component from sliding forward and letting the ocean in. The grubscrew arrangement is inadequate.

It's a cheap and easy fix. It's what the PSS people insist on for all their commercial products. Why they haven't responded to the many 'failures in service' of their yottie product demands an explanation.

In case you're wondering, I have very good reason to be emphatic!

My boat nearly sank a month ago because the rotor had slipped up the prop shaft without me realising. Luckily I was in harbour and had a friend to pump the bilges whilst I repaired it. If this had happened at sea and at night, I would have lost the boat. I now have 2 jubilee clips in place to prevent rotor slippage; the grub screws alone are not adequate.

 

[MoodySabre]

I read on another forum of someone having cut a length of plastic pipe the required length between the coupling and the compressed bellows. He cut the pipe lengthways and put it over the propshaft to hold it in the correct position whilst he put the grub screws in. He has left the pipe in place.

After 4 years with my PSS you have planted the seeds of paranoia and now I'll have to put a jubilee clip on it! Thanks.

 

[rogerthebodger]

I cut a piece of stainless steel pipe lengthwise to fit between the rotor and my coupling and fixed the pipe in place with one or two worm drive clips.

Or get one of these

 

[zoidberg]

Is it a normal hexagon allen key for the set screws? I've got spare set screws on the boat but cannot remember if they came with a special key.

I think you'll find the set screws require a NON-metric hex key.... an obscure 'Murricain standard.

Also, the makers' website indicates that the necessary torque setting is critical to performance - too little, and they'll slip. Too much, the points will squash, and they'll slip. That requires a suitable torque wrench with a suitable range of settings. Not every 'installer' uses a torque wrench, and it is suspected that the set screws are often done up manually until they seem about right.....

Once the rotor component slips, the ocean comes in.....

That happened to a friend and I in Falmouth Harbour. Had it not been for the local ILB exercising nearby with a salvage pump to hand, we likely would have sunk on the V-mooring.
The local yard which took on the repair work mentioned they had several near-identical PSS failures.

I'm quite willing to accept that, if perfectly installed, the devices perform perfectly. However, they are not fail-safe. And - according to the makers' website - they do require periodic inspection and maintenance.

 

[mbroom]

I think you'll find the set screws require a NON-metric hex key.... an obscure 'Murricain standard.

Also, the makers' website indicates that the necessary torque setting is critical to performance - too little, and they'll slip. Too much, the points will squash, and they'll slip. That requires a suitable torque wrench with a suitable range of settings. Not every 'installer' uses a torque wrench, and it is suspected that the set screws are often done up manually until they seem about right.....

Once the rotor component slips, the ocean comes in.....

That happened to a friend and I in Falmouth Harbour. Had it not been for the local ILB exercising nearby with a salvage pump to hand, we likely would have sunk on the V-mooring.
The local yard which took on the repair work mentioned they had several near-identical PSS failures.

I'm quite willing to accept that, if perfectly installed, the devices perform perfectly. However, they are not fail-safe. And - according to the makers' website - they do require periodic inspection and maintenance.

Mine was professionally installed 2 years ago. If a simple jubilee clip can prevent a catastrophic failure, then why is it not recommended? AFAIK there is nothing about checking the rotor positioning and grub screw torques on the maintenance schedule.

 

[vyv_cox]

I have repositioned my stainless steel rotor a couple of times and reversed it when the face became pitted. A small hex key is provided with the seal unit, which suggests that they do not expect users to use accurate torque figures. I certainly did not, just used the key, and all has been well for many years

 

[zoidberg]

I note the PYI-PSS company's website has been considerably enhanced since I first sought to explore what had led to our near-sinking - an incident with a degree of good luck, for we should have been halfway across the Western Channel, had we not gone to Falmouth first.

A 'web search' later discovered a number of other reported incidents - some discussed on here - and querying wizened and reputable yard foremen in half-a-dozen West Country yards elicited their knowledge of 'recurring problems' with some PSS seals. We had our 'near-sinking' problem, it nearly killed us, and the US manufacturer and the European agent had known of the potential for failure due to several ongoing complaints from several corners of the globe. Certainly, there are many who have had no problems with the kit. This is, however, reminiscent of the recent problems with the Boeing 737 Max crashes.... the company knew of the problem and did nothing.

Here's what their website says now:

....Use approximately 6 foot pounds of torque for shafts 3/4" to 1-3/8" and 8 foot pounds of torque for shafts 1-1/2" to 3-3/4"

....The PSS bellows must be inspected on a regular basis (i.e., no less than at least every 6 months under most circumstances) and checked for any signs of deterioration (cracks, splits, tears, brittleness, or other signs). Upon any sign of deterioration the bellow must be replaced.
As preventive maintenance the bellow should be replaced no less than every 6 years on the Type A Seal, and 8 to 10 years on the PSS PRO Seals, regardless of its apparent condition

....If the boat sits idle for a long period of time (generally 3 months or more), it is necessary to move the carbon face back to allow a small amount of water to enter the boat.

....Do not re-use the supplied cupped pointed set screws. If multiple tightening has flattened the cupped-point set screw, replace the affected screw with a new one.

It is unrealistic to expect anyone other than an experienced engineer/fitter to do up set screws MANUALLY and judge the applied torque accurately. Once they have been done up, they cannot be checked other than by removal. Refitting previously-used set screws is specifically embargoed.

In the absence of an available 'locking collar' the fitting of a stainless Jubilee hose clip - or perhaps two, opposed, for balance - seems a cheap and easy solution to a known problem..... which cost our insurers little shy of £20,000 and which could have lost the boat.