Stern Gland Packing

[rusty69]

I have my narrowboat out of the water for blacking for a week. Having finished the paintwork, I decided to look at the stern gland packing as it hasn't been changed in my ownership.

I was expecting to remove the lock nut, nuts and pusher and view some very old packing rope. I have removed the pusher and it appears there is a plastic/rubber seal instead. Is this normal? or is the packing rope behind the seal. I don't want to disturb it incase I cant get a replacement in time.

Due back in the water next Friday.

Have attached a photo.

Many thanks in advance

[Tony Brooks]

It looks a bit like modern PTFE packing to me but I can't see the bottom, I suspect there may be the join there.

[rusty69]

It looks a bit like modern PTFE packing to me but I can't see the bottom, I suspect there may be the join there.

Thanks Tony. It hasn't been changed in at least 15 years, were the modern ones about back then?

[rusty69]

It looks a bit like modern PTFE packing to me but I can't see the bottom, I suspect there may be the join there.

I have had a close look all round, and can't see a join.I suspect to replace it, may mean removing the shaft.

[alan_fincher]

I have had a close look all round, and can't see a join.I suspect to replace it, may mean removing the shaft.

 

I very much doubt it is a continuous ring around the shaft.

 

I'm pretty certain that there will be a join, even if you can't see it.

 

The normal thing is that each end of a length of packing is cut at something like 45 degree slant, the whole think being slightly over length so it presses firmly together.

 

The end result, particularly after years of compression, may well look like there is no join, but if you try taking the first length out, I bet you quickly find one.

[rusty69]

 

I very much doubt it is a continuous ring around the shaft.

 

I'm pretty certain that there will be a join, even if you can't see it.

 

The normal thing is that each end of a length of packing is cut at something like 45 degree slant, the whole think being slightly over length so it presses firmly together.

 

The end result, particularly after years of compression, may well look like there is no join, but if you try taking the first length out, I bet you quickly find one.

Thanks Alan. I must admit,I can see no join, but its been in there for years. If it is PTFE, does it need to be replaced like for like, or will something else be suitable. The gland itself doesn't leak too badly, but the adjustment is probably less than 15mm on the pusher.

 

The material in there at the moment seems quite hard. I may just measure it up for next time and do it then.

[alan_fincher]

Unless your stern gear has a very short overall range of adjustment, I'm struggling to see how you only have around 15mm of adjustment left.

 

I'm basing that on the act that from your pictures it really doesn't look like the face of the packing we are seeing is more than 10mm or so recessed.

 

I guess I may be misreading it.

 

I'd say 15mm is adjustment for many years to come, but if the packing really is that old, it may well be less effective than it could be, and is probably now quite hard and inflexible.

I'd bit the bullet, and pull at least one ring out to see what it is like. There will probably be 2 or 3 in total.

I would say that other than the size, you do not have to replace like with like.

The size is important though - probably 5/16" (8mm), but measure it to be sure. Ignore anybody who says other sizes can be squashed one way or the other to make them fit. This is a very bad idea, in my experience.

[rusty69]

The remaining adjustment is 9mm:-

 

 

The packing is just over 5mm in:-

 

 

 

 

I will check out the local chandlery and see if they have anything in stock before removing the packing

 

 

Edited to remove duplicate photo.

Edited June 12, 2016 by rusty69

[rusty69]

The pusher appears to be only 15mm in length!

The studs appear to be oversized for the pusher size, or am I missing something?

[alan_fincher]

For some reason your images are refusing to display full size for me. No idea why - others still will.

 

Two look like they are probably the same?

 

The "pusher" only being 15mm long seems unusual to me, though I have not taken that many apart, I'll admit.

[rusty69]

For some reason your images are refusing to display full size for me. No idea why - others still will.

 

Two look like they are probably the same?

The "pusher" only being 15mm long seems unusual to me, though I have not taken that many apart, I'll admit.

Sorry, not sure what happened with pics.

 

Two are the same, posted in error. I tried to correct by editing, but not sure how to remove pic.

 

Seems like an odd setup, but like you have not taken many apart. Perhaps some other forum members will be along shortly to advise on typical pusher lengths.

 

Thanks for all your help and advise so far.

[alan_fincher]

Actually, on thinking about it again, I'm not sure.

 

On the one hand they don't need a huge travel for adjustment once all fully correctly installed. The packing will not normally go down that much over time.

 

On the other hand, if your packing is a typical 8mm, and the pusher s only 15mm, then that is less than the thickness of two rings, and a ring is the smallest unit you could install.

 

So if you put in (say) two rings, and that resulted in the pusher just being able to reach them, but not compact them, that would be no good, (of course), but just adding a third ring would then move the pusher out by 8mm, at which point you have only 7mm of adjustment, even before you start doing it up.

 

(Of course it's possible your packing is not 8mm, which would alter the sums).

I would have thought a "pusher" length of more like 25mm is better. That way you should be able to get enough (say) 8mm rings installed, have them under compression, and still have well over the thickness of one ring left before you run out of adjustment.

Even so, I think if you take out however many rings are in there, and put the same number back, then it should be fine - just there will be less spare adjustment than on some installations.

 

I may not have said that too well - I hope my logic is not too garbled!

[rusty69]

Actually, on thinking about it again, I'm not sure.

 

On the one hand they don't need a huge travel for adjustment once all fully correctly installed. The packing will not normally go down that much over time.

 

On the other hand, if your packing is a typical 8mm, and the pusher s only 15mm, then that is less than the thickness of two rings, and a ring is the smallest unit you could install.

 

So if you put in (say) two rings, and that resulted in the pusher just being able to reach them, but not compact them, that would be no good, (of course), but just adding a third ring would then move the pusher out by 8mm, at which point you have only 7mm of adjustment, even before you start doing it up.

 

(Of course it's possible your packing is not 8mm, which would alter the sums).

 

I would have thought a "pusher" length of more like 25mm is better. That way you should be able to get enough (say) 8mm rings installed, have them under compression, and still have well over the thickness of one ring left before you run out of adjustment.

Even so, I think if you take out however many rings are in there, and put the same number back, then it should be fine - just there will be less spare adjustment than on some installations.

 

I may not have said that too well - I hope my logic is not too garbled!

That seems to make sense. I have measured the gap the packing fits in, to be 8mm. The pusher, as you say,seems to be on the short side, and to have any effect at all, the number of packing rings must be critical. Even so, leaving minimal scope for adjustment.

 

I guess the only way to find out is to pull the old rings. To be on the safe side, I will make sure I can get some new before I do. Perhaps if the prop shaft is ever removed, it would be prudent to have a longer pusher installed.

 

Still, it hasn't sunk so far, and is thirty years old, so obviously works ok.

 

Thanks again for your input.

[Richard10002]

When I had a stern gland, I seem to recall packing it until the packing was almost a little bit proud, and the first few turns of the packer forced it into the gap. That way, with a 15mm packer, you would have 15mm of adjustment, which should be more than enough.

[rusty69]

When I had a stern gland, I seem to recall packing it until the packing was almost a little bit proud, and the first few turns of the packer forced it into the gap. That way, with a 15mm packer, you would have 15mm of adjustment, which should be more than enough.

Did you compress the packing with the adjuster, and keep adding packing until it was almost proud?

[mross]

Was it leaking before? If it ain't broke don't fix it! Modern packings are very durable, especially at low revs and when the shaft is smooth and concentric, which yours appears to be. Personally, I would have some packing available of the correct size but leave it as is. You can always add a turn in service if necessary. Does the stern gland have a greaser? Not necessary if packing is PTFE. A slight drip from this kind of seal is beneficial as it provides cooling and lubrication. The 'pusher' as you call it is properly called a gland and the assembly a stuffing box. I've repacked stuffing boxes that have 60 to 100 bar pressure behind them (900 to 1500 psi) and well done they last a long time.

 

I'd suggest to cut a couple of turns, nicely chamfered at 45 degrees that fit snugly around the shaft, seal them in a ziplock bag and secure them nearby so they are handy if you need to repack the stuffing box in a hurry.

 

My boat has a little bilge pump that will cut in after the stern seal has dripped for a few weeks.

 

Yours appears to have a greaser as I see a copper pipe. If you decide to repack it you need to get all the packing out AND the lantern ring because there should be more packing behind that. Lantern ring is normally brass and split so that it can be changed without removing the shaft

 

 

To get all the packing out, a packing extractor, which is like a corkscrew, is very useful.

Edited June 11, 2016 by mross

[rusty69]

Was it leaking before? If it ain't broke don't fix it! Modern packings are very durable, especially at low revs and when the shaft is smooth and concentric, which yours appears to be. Personally, I would have some packing available of the correct size but leave it as is. You can always add a turn in service if necessary. Does the stern gland have a greaser? Not necessary if packing is PTFE. A slight drip from this kind of seal is beneficial as it provides cooling and lubrication. The 'pusher' as you call it is properly called a gland and the assembly a stuffing box. I've repacked stuffing boxes that have 60 to 100 bar pressure behind them (900 to 1500 psi) and well done they last a long time.

 

I'd suggest to cut a couple of turns, nicely chamfered at 45 degrees that fit snugly around the shaft, seal them in a ziplock bag and secure them nearby so they are handy if you need to repack the stuffing box in a hurry.

 

My boat has a little bilge pump that will cut in after the stern seal has dripped for a few weeks.

 

Yours appears to have a greaser as I see a copper pipe. If you decide to repack it you need to get all the packing out AND the lantern ring because there should be more packing behind that. Lantern ring is normally brass and split so that it can be changed without removing the shaft

 

To get all the packing out, a packing extractor, which is like a corkscrew, is very useful.

It only leaks slightly. It has a greaser. When the engine is stopped and grease applied, all leaks stop. The only reason I was considering replacing it at this stage, is that the boat is currently out of the water, and with limited adjustment on the pusher (gland), I would have to wait until next time the boat is out of the water to change the packing. I'm not sure for certain it is PTFE, only going on an earlier post.

 

I like the idea of having some packing on standby. Thanks for the suggestion.

 

 

How does the extractor remove the lantern ring in your example?

[alan_fincher]

The only reason I was considering replacing it at this stage, is that the boat is currently out of the water, and with limited adjustment on the pusher (gland), I would have to wait until next time the boat is out of the water to change the packing.

Not generally the case, actually.

 

It is usually perfectly possible to replace the entire packing with the boat in water.

 

This has been covered many times before on the forum.

[Richard10002]

Did you compress the packing with the adjuster, and keep adding packing until it was almost proud?

 

I cant remember the detail... I've only done it once, and it would have been about 9 years ago. I dont think I kept adding, just put enough in to fill the space, then compressed it with the packer...... until I got 4 drips a minute with the engine running, and the housing as hot as a warm cup of tea

[rusty69]

Many thanks for everyones help.

[bizzard]

The pusher needs to go a fair way in, after all its a supplement bearing to the main tube bearing and takes some of the stress and whopping around given to it by a rubber mounted engine without a twin UJ coupling in the drive line, as many boats are these days.

[rusty69]

The pusher needs to go a fair way in, after all its a supplement bearing to the main tube bearing and takes some of the stress and whopping around given to it by a rubber mounted engine without a twin UJ coupling in the drive line, as many boats are these days.

The pusher (gland) can go in a maximum of 15mm. If new gland packing is installed, leaving scope for adjustment, the pusher won't go in a fair way. The only way I can see of getting both is by having a longer pusher or little adjustment.

 

Hope that makes sense.

[bizzard]

The pusher (gland) can go in a maximum of 15mm. If new gland packing is installed, leaving scope for adjustment, the pusher won't go in a fair way. The only way I can see of getting both is by having a longer pusher or little adjustment.

 

Hope that makes sense.

Yes it makes sense. Is your engine rubber mounted without a twin UJ in the shaft (Aquadrive-Python drive or equivalent?

[Richard10002]

I didn't think the pusher actually touches the shaft in a bearing kind of way?

[rusty69]

Yes it makes sense. Is your engine rubber mounted without a twin UJ in the shaft (Aquadrive-Python drive or equivalent?

Yes, and yes.