PSS seal.... problem?

[PaulJ]

Following a question I asked on this forum some time back, I have just invested in, though not yet fitted, a PSS shaft seal. On showing it to a friend who is a well qualified engineer, though he liked the priciple he expressed concern over a potential problem and suggested a possible solution. Before I panic and spend more of my hard earned readies on having this solution made, I would like to asked anybody who has used one of these seals for some time if it really is a problem in practice.....

My seal is for a 1 1/2" shaft and so the stainless steel rotor is a fairly chunky piece of metal. As such, it will have a fair amount of inertia. The concern is that there will inevitably be some torsional vibration from the engine which is transmitted through the propshaft and this in turn will have to be transmitted to the stainless steel rotor via the two small grub-screws which hold it in place on the shaft. My friend thinks that in time, the rotor will creep round on the shaft and in doing so will probably score the shaft. This scoring will not be a problem until you have to remove the rotor.... then when it is replaced, the all-important O-rings are likely to be damaged.

I know from my previous question that a number of the users of this forum use the PSS seal..... have any of you had this problem or is it one of those theoretical possibilities that just doesn't happen in practice?

Thanks in advence

Paul.

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by PaulJ on 02/10/2003 14:21 (server time).</FONT></P>

 

[tome]

Paul

I had a PSS seal fitted a year ago and haven't seen any problems. The SS collar is held in place by two grubscrews, each fitted with a second locking screw. My shaft is 1.25" dia.

I haven't removed the collar so cannot be sure it hasn't scored, but not aware of any problems. My only concern was if the carbon was broken for any reason it would let a lot of water in, and I considered (but haven't yet) puttiing a jubilee clip in position which I could tighten onto the shaft if this happened.

Regards
Tom

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[aod]

Well I have had one for five or six years and I managed to bugger up one of the grub screws, but it's never moved and to be honest the only problem I have ever had was replacing the bellows after 4 years of use. As a precaution I did put a jubilee clip behind it just in case but I don't really think that it necessary.

Hope this helps

Richard

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[Paul_H]

Im interested in this myself. Ive currently got a conventional greasy string shaft seal and would like to change it to something more elegant. On another boat Ive used a Deap Sea which uses a similar principle to the PSS. My concern is with age hardening of the rubber concertina reducing the pressure between the seal surfaces. With the Deap Sea it was necessary to change the rubber bit after 3 or 4 years. Another concern was remembering to let water into the stern tube after launching to avoid the smell of burning tufnell used for the seal surface.

A look at the shaftseal.com site shows the PSS grub screws digging into the prop shaft between the O-rings and as you say are likely to score the shaft. Elegant system but poor design. Id be interested what your chum suggests as a solution -bet its expensive.

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[roger]

Stopelo - an alternative

I fitted a Stopelo seal - bought in Dunkirk at about £90 for 25 mm. shaft. Its working fine but I was worried about spares so I simply bought another one. I just couldnt work out which bits were likely to wear out first and the price was cheap enough for such a safety critical item.
You're quite right about the need to flood it when launching. I have a big notice up in the cabin - but probably one year I'll forget - Sods Law and old age

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[Avocet]

Re: Stopelo - an alternative

I've had no experience of the seals you speak of. My boat had an old-fashioned sterntube and a stuffing box and remote greaser for each end. I did, however, make my own universal joint coupling for it so I needed something to take the thrust from the propeller. I found a suitable bearing and it is clamped to the propeller shaft by a few very small (5 or 6mm - can't remember) grub screws. Considering this takes all the forward and reverse thrust of my mighty 12hp diesel and hasn't slipped in 5 seasons I'm fairly sure the part you're all discussing will be OK! If anything, I'd be more concerned (but not MUCH more!) with the end of the grub screw starting a fatigue crack in the shaft. If it's clamped at a point where the shaft has any tendency to "whip" there might be small, alternating bending loads on it in use. I don't know enough about it to say whether it's a valid concern though!

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[PaulJ]

Firstly, many thanks to you all for taking the trouble to reply.... and to PaulH the suggested remedy is to make a second similar stainless rotor and nearly (but not quite) cut it in half across it's diameter. Then drill and tap across the cut to take a bolt which when tightened will then close the ring so that it can be clamped onto the shaft just ahead of the original PSS Rotor. Thus the new rotor will be clamped tightly onto the shaft with a nice big bearing /gripping area and three or four bolts would pass through it into the PSS rotor to hold it and transmit the drive. It does seem to me to be a better way to do it but it would cost a bit to have the new collar made and I am not totally convinced that it is necessary.....

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[okierse]

I fitted a PSS 1.25" seal last winter as a replacement to an old Deep Sea Seal. No problems so far....does exactly what it said on the tin. Did fit a jubilee clip as a backup though.

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