Stern Gland Packing

[davidk65]

In having a general chat with others about stern glands and the packing there of. A number of interesting points came up.

Some(lucky)individuals said that their stern glands had never leaked and they never had the needed to adjust, just simply "turn the greaser". Others said that they needed to tighten the stern gland adjusting bolts, a couple of turns, every couple of months or so. The boaters that needed to tighten the gland, had all replaced the packing in the last two to three years and leaking was part of boating.

Question: Why do some leak and others apparently, don't leak?

Could it be down to different grades of packing material i.e. PTFE or Graphite packing?

Some said that when a stern gland is repacked it should be adjusted to the point were the prop shaft can no longer be turned by hand.

This raised another question; if this degree of tension on the gland is achieved, should this condition be maintained in all operational conditions i.e. the shaft cannot be turned by hand?

 

What say you?

 

David.

[nb Innisfree]

In having a general chat with others about stern glands and the packing there of. A number of interesting points came up.

Some(lucky)individuals said that their stern glands had never leaked and they never had the needed to adjust, just simply "turn the greaser". Others said that they needed to tighten the stern gland adjusting bolts, a couple of turns, every couple of months or so. The boaters that needed to tighten the gland, had all replaced the packing in the last two to three years and leaking was part of boating.

Question: Why do some leak and others apparently, don't leak?

Could it be down to different grades of packing material i.e. PTFE or Graphite packing?

Some said that when a stern gland is repacked it should be adjusted to the point were the prop shaft can no longer be turned by hand.

This raised another question; if this degree of tension on the gland is achieved, should this condition be maintained in all operational conditions i.e. the shaft cannot be turned by hand?

 

What say you?

 

David.

 

To my mind if a PythonDrive or Aquadrive or just a thrust bearing is fitted it will stop any sideways flexing of the shaft and minimise any gland adjustment.

 

When I fitted our packing I initially tightened the nuts up very tight so as to thoroughly bed the packing in then loosened the nuts until the shaft could be turned by hand, just detecting a slight drag. After that I adjusted it for a while until things had settled down and since then there has been no need for adjustment and no drips, been 5 years now.

 

Must add we have a PythonDrive which has a lot to do with it I think + I am very generous with the grease, if grease is needed to stop water leaking in then it's not going where it should and that is the outside via the bearing, packing should stop water not the grease.

 

Grease just manages to squeeze slightly into the inside but as it will take the least line of resistance it ensures grease goes ouside.

[Ex- Member]

It's just a matter of tweaking with it. We managed to get ours with minimal ingress of water occasional drip daily if cruising if you like. We only ever turned the greaser about half a turn before cruising, it never seemed to get too hot so assumed it was adjusted about as good as possible. I was told that some water should come through as this ensures the gland fibres a wet all the way through which helps cooling.

 

We've been on dry land for some time now, I'm wondering if the gland will need re-doing from scratch?

[nb Innisfree]

I was told that some water should come through as this ensures the gland fibres a wet all the way through which helps cooling.

 

I think there is a lot of mythology around this subject, our gland is watertight and runs nice and cool.

 

We are very generous with grease but when we were in dry dock recently it took a full greaser load before clean grease emerged outside pushing out quite a bit of water in the process.

 

So my way of thinking is make greasing the shaft a priority and keep water out, a small amount of grease inevitably escaping past the gland will ensure it lasts a long time.

[MoominPapa]

The first sign that adjustment is needed tends to be excess grease inside the boat rather than excess water. I don't know why.

 

MP.

[RobinJ]

In having a general chat with others about stern glands and the packing there of. A number of interesting points came up.

Some(lucky)individuals said that their stern glands had never leaked and they never had the needed to adjust, just simply "turn the greaser". Others said that they needed to tighten the stern gland adjusting bolts, a couple of turns, every couple of months or so. The boaters that needed to tighten the gland, had all replaced the packing in the last two to three years and leaking was part of boating.

Question: Why do some leak and others apparently, don't leak?

Could it be down to different grades of packing material i.e. PTFE or Graphite packing?

Some said that when a stern gland is repacked it should be adjusted to the point were the prop shaft can no longer be turned by hand.

This raised another question; if this degree of tension on the gland is achieved, should this condition be maintained in all operational conditions i.e. the shaft cannot be turned by hand?

There are a lot of variables!

Size and type of engine, associated vibration at different speeds, coupling method, engine mountings, gearbox and stern gland type, prop size, mileage, age, wear and tear, alignment and of course temperature!

A good gland well packed with good alignment and little vibration will last years with very little water penetration. If the packing dries out (either because of over tightening or standing on the hard) then it is likely to be worse, especially if when worn a new piece is simply inserted on top. Overheating or lots of debris on the prop may change the alignment of the porp of create wear which makes leaks more likely.

Basically its a question of luck!

[PaulD]

When I checked and corrected the prop shaft alignment earlier this year I noticed a significant reduction in the amount of water dripping from the gland.

 

Obviously a factor.

 

Paul

[BEngo]

The first sign that adjustment is needed tends to be excess grease inside the boat rather than excess water. I don't know why.

 

MP.

 

 

That's because the small gap down past the bearing has now become harder for the grease to get down than the gap by the stuffing box and the grease takes the line of least resistance.

 

N

[davidk65]

That's because the small gap down past the bearing has now become harder for the grease to get down than the gap by the stuffing box and the grease takes the line of least resistance.

 

N

That's a very interesting point. Can this "passage way" be cleaned out and how does one go about it?

Is it: a) A job that can be done at any time or only when the gland is to be repacked? Or b)Is it a job that can only be tackled when the boat is out of the water/?

David.

[nicknorman]

..., it never seemed to get too hot so assumed it was adjusted about as good as possible...

How hot is too hot? I recently adjusted ours, it turns quite freely but does get fairly hot, you can touch it but not hold it for long, so maybe 60 deg. Is that too hot?

[bizzard]

How hot is too hot? I recently adjusted ours, it turns quite freely but does get fairly hot, you can touch it but not hold it for long, so maybe 60 deg. Is that too hot?

I'd say yes.The grease would be almost running like oil at that temp.

[nb Innisfree]

That's a very interesting point. Can this "passage way" be cleaned out and how does one go about it?

Is it: a) A job that can be done at any time or only when the gland is to be repacked? Or b)Is it a job that can only be tackled when the boat is out of the water/?

David.

 

What he's saying is the grease when pumped into the space around the shaft will either go backwards between the shaft and bearing to the outside (which you refer to as a "passage way") or forwards past the stuffing gland, the direction it takes depends on which route is easier, slack stuffing gland and it will go that way, tight stuffing gland will prevent grease exiting there so the only route out is between the shaft and bearing.

 

To clean this "passage way" tighten gland right up up and keep pumping until clean fresh grease appears at the exit of the propshaft, it may take a complete greaser full or more.

 

Don't forget to readjust packing gland.

[bizzard]

It might be best filling the greaser with light oil and forcing it through to clear the lubrication groove,which should always be positioned at the top on plain bearings like sterngear. bizzard

[Timleech]

It might be best filling the greaser with light oil and forcing it through to clear the lubrication groove,which should always be positioned at the top on plain bearings like sterngear. bizzard

 

Sterngear maybe, but not plain bearings generally.

 

Tim

[n.b.Goldie]

On my little ship the tube from the greaser enters the 'stuffing box' underneath rather than on top. Is this a 'bad thing' or does it not matter?

 

Thanks

Ditchdabbler

[bizzard]

Sterngear maybe, but not plain bearings generally.

 

Tim

On non continuous pressure lubricated plain bearings,the groove should always be positioned on the non load side usually the top to allow lubricant to quickly surround the shaft-,axle,the bearing will soon wear and fail if not.

The old railway companies found this out way back,by changing from top groove to bottom groove,none load side of locomotive axle boxes and so doubled their life and so prevented hot boxes and failure,the practice was still continued later with mechanical lubricators fitted.My old hobby of constructing and running 5''gauge model steam loc's also prooved this.So lub groove always on none load side. bizzard

Edited September 6, 2011 by bizzard

[Iain_S]

On non continuous pressure lubricated plain bearings,the groove should always be positioned on the non load side usually the top to allow lubricant to quickly surround the shaft-,axle,the bearing will soon wear and fail if not.

The old railway companies found this out way back,by changing from top groove to bottom groove,none load side of locomotive axle boxes and so doubled their life and so prevented hot boxes and failure,the practice was still continued later with mechanical lubricators fitted.My old hobby of constructing and running 5''gauge model steam loc's also prooved this.So lub groove always on none load side. bizzard

 

On a wheel axle, isn't the top of the bearing the load side?

 

Iain

[bizzard]

On my little ship the tube from the greaser enters the 'stuffing box' underneath rather than on top. Is this a 'bad thing' or does it not matter?

 

Thanks

Ditchdabbler

I don't think it matters. The gland unit probably screws onto your shaft bearing as most do,they probably couldn't get the extra half turn on the thread when fitting so stopped at the bottom.bizzard.

 

On a wheel axle, isn't the top of the bearing the load side?

 

Iain

Yes i got mixed up. I've edited my previous post to correct this. bizzard.

[Timleech]

On non continuous pressure lubricated plain bearings,the groove should always be positioned on the non load side usually the top to allow lubricant to quickly surround the shaft-,axle,the bearing will soon wear and fail if not.

The old railway companies found this out way back,by changing from top groove to bottom groove,none load side of locomotive axle boxes and so doubled their life and so prevented hot boxes and failure,the practice was still continued later with mechanical lubricators fitted.My old hobby of constructing and running 5''gauge model steam loc's also prooved this.So lub groove always on none load side. bizzard

 

But.......

One reason for a lubrication groove is to hold some lubricant ready for use after a bearing has been standing.

This, particularly with oil, *has* to be in the bottom because that's where gravity will keep the oil. No good having it in the top for that purpose.

 

Tim

 

On my little ship the tube from the greaser enters the 'stuffing box' underneath rather than on top. Is this a 'bad thing' or does it not matter?

 

Thanks

Ditchdabbler

 

Probably done because parts of the sterngear have been replaced at some time, or the tube has worked loose and leaked. That will be the position the gland assembly has ended up when fully tightened, it's more important to have it tight than to look pretty.

 

Tim

[bizzard]

But.......

One reason for a lubrication groove is to hold some lubricant ready for use after a bearing has been standing.

This, particularly with oil, *has* to be in the bottom because that's where gravity will keep the oil. No good having it in the top for that purpose.

 

Tim

As plain bearings are for relatively low speed use the load bearing surface will retain a film of oil enough for the first half turn at start up.A groove on both none and load side were tried but generally not used as it reduces the bearing surface a little more. Refer to 'Fowlers Mechanics' machinists pocket book.

 

 

Probably done because parts of the sterngear have been replaced at some time, or the tube has worked loose and leaked. That will be the position the gland assembly has ended up when fully tightened, it's more important to have it tight than to look pretty.

 

Tim

[nb Innisfree]

Some have the grease entering on the bottom to keep it out of the way of big clod hopping boots.

[Timleech]

Depends what you mean by low speed. Plain bearings are the norm for internal combustion engine crankshafts, for instance.

 

Tim

 

Edit to add - yes as a general rule bearings should be oiled from a 'low pressure' area as bizzard has said, but it's not always the only way. Gardner crankshaft main bearings are oiled from the bottom, for instance . As regards sterngear, the bearings are running at low pressure anyway (big surface relative to load) and with generous clearances, and the biggest load is quite likely to be from outside forces such as alignment of engine or other bearings etc., rather than the weight of the sterngear itself. The shaft is also very likely to describe a slight oscillating motion in service. Personally I wouldn't get hung up about where the oil groove is sitting in the stuffing box.

 

Tim

Edited September 7, 2011 by Timleech

[bizzard]

Depends what you mean by low speed. Plain bearings are the norm for internal combustion engine crankshafts, for instance.

 

Tim

 

Edit to add - yes as a general rule bearings should be oiled from a 'low pressure' area as bizzard has said, but it's not always the only way. Gardner crankshaft main bearings are oiled from the bottom, for instance . As regards sterngear, the bearings are running at low pressure anyway (big surface relative to load) and with generous clearances, and the biggest load is quite likely to be from outside forces such as alignment of engine or other bearings etc., rather than the weight of the sterngear itself. The shaft is also very likely to describe a slight oscillating motion in service. Personally I wouldn't get hung up about where the oil groove is sitting in the stuffing box.

 

Tim

I think we ought to leave internal combustion out of it as they're a different high precision animal and as you say forces coming in from all angles. No i'm talking about just low speed shafting,axles ect with generous clearances. Most plain motion bearings and axle bearings on steam loco's were all given generous clearances to cope with temperature fluctuations and huge unusual and in the main unbalanced angular stresses.When steam was shut of, they clanked even when new. Its interesting that towards the end of steam railway loco's BR started to use enormous canon boxed Timken tapered roller bearings on driving wheel axles of around 1ft diameter, and smaller ones for certain other motion parts.But only a few were built as such before steam power was withdrawn. bizzard

[David Mack]

On a wheel axle, isn't the top of the bearing the load side?

 

Iain

 

Depends if its a fixed axle on which the wheel rotates, or if the axle rotates with the wheels in fixed bearings.

 

David

[Timleech]

Depends if its a fixed axle on which the wheel rotates, or if the axle rotates with the wheels in fixed bearings.

 

David

 

From what I can remember, older railway wagons usually only had a top half bearing

 

Tim