Gland Packing/Alignment

[rusty69]

Whilst I wait for the rain to stop and painting prep to continue, my attention turns to next weeks job.

 

As the boat is out of the water, I thought I would see how easy it is to replace the gland packing, and buy some ready for the job.

 

Measured with two drill bits (see pic), to determine replacement size, I was a bit surprised to see they are quite different.

 

One measures 8.75mm, the other 7.35 mm.

 

Is this normal?

Is it indicative of a misaligned shaft?

What size replacement should I get, or are there bigger problems here?

PTFE or Graphite?

 

For perspective, all runs nice and smoothly, but it does drip at quite a rate when under way. A few turns on the greaser stop the drips dead though.

 

Many thanks

Edited June 20, 2023 by rusty69
spelling

[Tracy D'arth]

Yes, the shaft is half a millimetre out of alignment in the horizontal. But what about the vertical plane? More likely to be important due to sinking engine mountings.

8mm - 5/16" packing required. I prefer graphite, its old school and has never let me down.

[Bee]

I would imagine the shaft is a bit off centre but I expect the same is true of many boats. I would also guess that the shaft is not rotating in an ellipse or wobbling about and if it was my boat I would reassemble the whole thing and forget about it, there seems to be plenty of packing in there and unless it starts to let in water I would leave it alone, if it ain't broke etc.

[rusty69]

12 minutes ago, Tracy D'arth said:

Yes, the shaft is half a millimetre out of alignment in the horizontal. But what about the vertical plane? More likely to be important due to sinking engine mountings.

8mm - 5/16" packing required. I prefer graphite, its old school and has never let me down.

Thankyou.

 

The bottom gap measure 8.1mm. The top around 8.5mm.

 

Will 5/16 fit without alignng the shaft, or must this be done first? There is a huge SKF bearing that would presumably need adjusting.

14 minutes ago, Bee said:

I would imagine the shaft is a bit off centre but I expect the same is true of many boats. I would also guess that the shaft is not rotating in an ellipse or wobbling about and if it was my boat I would reassemble the whole thing and forget about it, there seems to be plenty of packing in there and unless it starts to let in water I would leave it alone, if it ain't broke etc.

Ok, thanks. Its not a major issue, but there is also not much more scope for adjustment on the pusher.

[Bee]

Ah, if you have an Aquadrive or Pythondrive with a big SKF bearing I think it is self aligning so it has probably aligned itself to the misalignment (!) So yes, if you want to get it straight you will indeed have to shift it around a bit to centre the shaft better and then re pack the gland 

[rusty69]

1 minute ago, Bee said:

Ah, if you have an Aquadrive or Pythondrive with a big SKF bearing I think it is self aligning so it has probably aligned itself to the misalignment (!) So yes, if you want to get it straight you will indeed have to shift it around a bit to centre the shaft better and then re pack the gland 

No Aquadrive or Pythondrive.

[David Mack]

18 minutes ago, rusty69 said:

Ok, thanks. Its not a major issue, but there is also not much more scope for adjustment on the pusher.

Since the packing is only just below the surface of the gland there should be plenty of adjustment left on the pusher. How long is the projecting cylindrical part on your pusher?

[rusty69]

12 minutes ago, David Mack said:

Since the packing is only just below the surface of the gland there should be plenty of adjustment left on the pusher. How long is the projecting cylindrical part on your pusher?

14mm total, with 8.1mm adjustment remaining.

Edited June 20, 2023 by rusty69

[Bee]

Hmm. realigning the engine is a sod of a job and presumably you have some sort of flexible coupling that is coping with a little bit of movement from flexible mounts if you have them. Shifting the SKF bearing is probably a case of filing the holes in the plate to which it is mounted till the shaft centres better. A tedious job but easy enough if you can get at it, might be worth it.  I think you probably have plenty of packing in there but one extra ring of something soft wouldn't hurt, just don't overtighten it.

[rusty69]

2 minutes ago, Bee said:

Hmm. realigning the engine is a sod of a job and presumably you have some sort of flexible coupling that is coping with a little bit of movement from flexible mounts if you have them. Shifting the SKF bearing is probably a case of filing the holes in the plate to which it is mounted till the shaft centres better. A tedious job but easy enough if you can get at it, might be worth it.  I think you probably have plenty of packing in there but one extra ring of something soft wouldn't hurt, just don't overtighten it.

Yes, there is an R&D type flexible coupling in there. Shifting the SKF bearing looks like a pig of a job, probably outside my pay grade. I think I will leave it, and perhaps add a bit more packing, as you suggest.

 

Thanks

[David Mack]

8 minutes ago, rusty69 said:

14mm total, with 8.1mm adjustment remaining.

So the packing is less than 6mm below the face of the gland. So you don't have room to fit another 8mm ring of packing.

[rusty69]

1 minute ago, David Mack said:

So the packing is less than 6mm below the face of the gland. So you don't have room to fit another 8mm ring of packing.

Good point.

[Tracy D'arth]

It doesn't need repacking!

[Rincewind]

3 hours ago, rusty69 said:

One measures 8.75mm, the other 7.35 mm.

 

As the packing thickness is 8mm, it follows then that there is a gap between shaft and packing on one side which is why your gland is leaking excessive water.  No amount of renewing, tightening/squashing the packing will alter that fact.  It may cover it up temporary, but - Ostriches and sand mentality would then apply here.

 

Ideally, as Tracy suggests, it would be better if the shaft was aligned so that it is concentric with the internal diameter of the gland, which means decoupling the prop shaft from the drive while this is carried out.  And then, and only then, align the engine/gearbox to the propeller shaft.  But from what I have gleaned so far from this thread, I suspect starting this task would open a whole can of worms and the resulting total cost in monetary terms may exceed the cost of a few turns of packing.

 

An Ideal time to sort it out though, while the boat is high and dry.

 

For reference, the gland packing is designed to not only (A) Create a Dam to hold back the bulk of the water that migrates through the propshaft bearing but also

(B) Act as a reservoir of water in order to dissipate heat created by the friction between the shaft and the surface of the packing when the shaft is rotating. 

It is not designed to act as a bearing, which, from this scenario, it appears it is!  (And putting undue load on the packing at one side compounding the issue!)

 

Be aware, this type of gland is designed to drip water during normal running.  Not only do the drips carry away excess heat, they are a visual indication that cooling is taking place and all is well.  The "Rate of Drip" is controlled by judicial adjustment of the Gland Follower - (often referred to as the "pusher") and should not be tightened excessively which will damage both packing material and shaft.   

 

Just as a check, does the gland follower enter the gland (by hand) without restriction or excessive force and then if you rotate the gland follower 180 degrees does it still enter the gland without restriction or excessive force?

[Tacet]

Apologies for my ignorance, but is not the alignment of the propeller shaft largely determined by the stern tube?  If so (and assuming the shaft and tube are not excessively overly worn and are straight), if the gland is not concentric with the shaft - it suggests these two are misaligned, most sensibly pointing the finger at the gland. 

 

[Rincewind]

Thats true in most circumstances but the OP said there was another bearing, an SKF type on the shaft at some point but not shown in the pictures and the stuffing box assembly is usually screwed onto the stern tube.

Edited June 20, 2023 by Rincewind

[Tony Brooks]

9 minutes ago, Tacet said:

Apologies for my ignorance, but is not the alignment of the propeller shaft largely determined by the stern tube?  If so (and assuming the shaft and tube are not excessively overly worn and are straight), if the gland is not concentric with the shaft - it suggests these two are misaligned, most sensibly pointing the finger at the gland. 

 

 

No, because the packing acts as a front bearing, as may the back of the gland casting, so on its own the shaft will always be in the centre of the tube.  If anything forces the shaft out of line, the front bearing on the shaft will wear. When engines drop on rubber mounts, and it is not rectified, you will find glands with oval holes worn by the shaft running out of alignment. In this case, the OP seems to have a plumber or thrust block on his shaft between the gland and a semi-flexible coupling, so it looks as if, for some reason, that block is out of alignment with the stern tube and thus the shaft, it seems to be forcing the shaft to one side and down.

[Rincewind]

7 minutes ago, Tony Brooks said:

No, because the packing acts as a front bearing, as may the back of the gland casting, so on its own the shaft will always be in the centre of the tube.  If anything forces the shaft out of line, the front bearing on the shaft will wear.

 

And thereby lies the problem, i.e. boat builders / installers and to a lesser extent, owners using the stuffing box / gland as a convenient bearing, which it is not and was never designed to be.  The stuffing box is screwed onto the stern tube to enable the two components to be concentric with one another.  In the OP's case, (we are led to believe), another bearing - an SKF - has been fitted to the shaft (on a bearer we hope & presume 😁) some distance away from the gland in order to align the front of the shaft with the stern tube bearing.  This arrangement is good engineering practice as, with the shaft now suspended between two bearings it leaves the stuffing box gland assembly to do what it was solely designed to do - namely - to create a Dam and a cooling jacket around the shaft.  (a small amount of water will penetrate the weave of the packing creating a mini reservoir and help it remain supple).

 

From the evidence we have it would seem (but not conclusive) that the engine/gearbox has become mis-aligned and forced the SKF bearing to one side together with the shaft thereby accounting for the discrepancy in the OP's measurements.

 

51 minutes ago, Tony Brooks said:

you will find glands FOLLOWERS with oval holes worn by the shaft running out of alignment

My Capitals & BOLD!

 

Which is why I asked the OP if the gland follower would fit into the stuffing box 180 degrees about.  As we cannot examine the gland follower for ovality ourselves and should it transpire that indeed it does not fit when turned 180 degrees, it would be another indication of misalignment.

[rusty69]

4 hours ago, Rincewind said:

But from what I have gleaned so far from this thread, I suspect starting this task would open a whole can of worms and the resulting total cost in monetary terms may exceed the cost of a few turns of packing.

 

An Ideal time to sort it out though, while the boat is high and dry.

 

Agreed, but its the Ostrich approach for me. I'm too engrossed in the painting to try and re align anything.

 

 

4 hours ago, Rincewind said:

   

 

Just as a check, does the gland follower enter the gland (by hand) without restriction or excessive force and then if you rotate the gland follower 180 degrees does it still enter the gland without restriction or excessive force?

I will take a look when I get a minute. Thanks for your input.I'm pretty sure its an easy fit, though haven't tried rotating it.

26 minutes ago, Rincewind said:

From the evidence we have it would seem (but not conclusive) that the engine/gearbox has become mis-aligned and forced the SKF bearing to one side together with the shaft thereby accounting for the discrepancy in the OP's measurements.

Here is a pic of the bearing I took earlier. Obviously it doesnlt show the complete installation, but forward of that is an R&D type flexible coupling.

[Bee]

Never seen one like that. Hefty lump though. Don't know if is a thrust bearing but whatever it is it just needs a shim or two under the bolts to lift it a fraction and if it has oval bolt holes a tap with a hammer to move it sideways a bit to centre the shaft (if you are lucky) or a bit of filing (if you are not) to let it slide sideways a fraction and the job is done. The Centaflex should cope with the slightly different alignment. It is possible that the packing will need replacing as it goes hard and might not take up the new alignment but It's probably been like that for years and will carry on for many more.

[rusty69]

19 minutes ago, Bee said:

Never seen one like that. Hefty lump though. Don't know if is a thrust bearing but whatever it is it just needs a shim or two under the bolts to lift it a fraction and if it has oval bolt holes a tap with a hammer to move it sideways a bit to centre the shaft (if you are lucky) or a bit of filing (if you are not) to let it slide sideways a fraction and the job is done. The Centaflex should cope with the slightly different alignment. It is possible that the packing will need replacing as it goes hard and might not take up the new alignment but It's probably been like that for years and will carry on for many more.

If I get the painting done, I might have a closer look. I poked the packing with a screwdriver earlier, it wasn't rock solid, but it also wasn't soft. I know for a fact it hasn't been changed in over 20 years, so may be due.

1 hour ago, Rincewind said:

Which is why I asked the OP if the gland follower would fit into the stuffing box 180 degrees about.

The answer, is no, it won't.

Edited June 20, 2023 by rusty69

[Rincewind]

Thanks for the reply.

That seems to confirm that the shaft is out of line and that the bore of the gland follower is now oval due to being worn away by the shaft.  Do not worry too much about the ovality of the gland follower, it is not a big deal and it can be reused again.  But you do need to re-align your prop shaft etc.

Where is the boat ashore at the moment?  I may be able to offer some help if you wish and your not too far away.

[rusty69]

32 minutes ago, Rincewind said:

Thanks for the reply.

That seems to confirm that the shaft is out of line and that the bore of the gland follower is now oval due to being worn away by the shaft.  Do not worry too much about the ovality of the gland follower, it is not a big deal and it can be reused again.  But you do need to re-align your prop shaft etc.

Where is the boat ashore at the moment?  I may be able to offer some help if you wish and your not too far away.

From what you say, it sounds like it is. 

 

That's an incredibly generous offer, thank you. The boat is out of the water in Northamptonshire, however, our primary goal is to DIY 2 pack epoxy, which we probably won't have completed until early next week. 

 

The stern gland repacking was supposed to be an extra whilst waiting for the paint to dry.

 

Alas, it appears to be a bigger problem than I first thought,and probably one beyond my skills. 

 

Thanks for the offer though, most kind. 

 

 

............. 

I'm pretty good at following simple instructions, so if any one here would like to talk me through the process, and thinks it's doable over the Internet (assume rincewind is in Shropshire), then I don't mind having a go at it next week. 

 

I have tools, I don't have packing, and I don't have any shims. I probably have a micrometer. I do have a vernier. 

 

I should say, that I have tried aligning a shaft on another boat with little success. 

 

If anyone thinks it's possible, please let me know if I should buy some new packing, and other bits. 

 

 

 

I also have, what I suspect is a dial test indicator and stand, but not a scoobies how to use it.

Edited June 20, 2023 by rusty69

[rusty69]

I ordered some graphite packing, which arrived today.

 

It's unlikely I have the technical ability to align the engine.

 

Is the packing likely to keep, or does it have a use by date?

[Tracy D'arth]

Just now, rusty69 said:

I ordered some graphite packing, which arrived today.

 

It's unlikely I have the technical ability to align the engine.

 

Is the packing likely to keep, or does it have a use by date?

There is no best before date.  Carbon is almost inert!