Stern Gland Packing

[Old Son]

I'm blacking my boat next year and thought it a good idea to replace the stern gland packing. How do I measure the size of packing I need whilst the boat is in the water? The only way I can see is remove the two nuts, withdraw the slider and measure with a Vernier gauge. Is there any other way please?

[Alan de Enfield]

5 minutes ago, Old Son said:

Is there any other way please?

1) I believe there are only two-sizes, by a length of each.

2) Find someone with the same gland / shaft size and ask them

3) Wait till you get it out of the water - It'll be out for at least 7 days so you can measure it, nip to the chandlers (or buy on line with next day delivery) and pop it back in.

[Mike Adams]

Measure the OD of the shaft and the OD of the slider, subtract one from the other and divide by 2 - probably 6mm or 1/4"

[Joe Bourke]

Slide the clamp back, use drill bits to test the fit along the prop shaft into the gland.  You could use pencils, pens, or crayons to give you an idea and measure them.

[bizzard]

Most common on narrowboats is 5/16''  8mm,   but get 1/4'' too just in case.

[Old Son]

Thanks all. 

[Ray T]

Get a set of metric and imperial drill bits and see which one fits in the gap.

[Tony Brooks]

Well as far as gland packing is concerned 6mm or 1/4" and 8mm or 5/16" and10mm or 3/8" are interchangeable.

[Slim]

4 minutes ago, Ray T said:

Get a set of metric and imperial drill bits and see which one fits in the gap.

Beat me to it. Think go / no go guage

[bizzard]

Personally I'd fit the correct size packing, as I said earlier Narrowboats with 1/1/2'' shafts are usually 5/16'' 8mm packing. I wouldn't use any other size in it.

[Old Son]

11 hours ago, Ray T said:

Get a set of metric and imperial drill bits and see which one fits in the gap.

But I would then need to remove the slider? If I have to I will but I was asking if there was another way without removing the slider.

[Tony Brooks]

12 minutes ago, Old Son said:

But I would then need to remove the slider? If I have to I will but I was asking if there was another way without removing the slider.

 

Yes, as describe by Mike in post 3 as long as you have a pair of calipers. That is unless the packing is so far gone the flange on the slider is hard against the stern gland housing. Without a photo there is always the possibility the OPs gland may not have a visible slider or the packing is in a great big nut affair.

[Slim]

If you decide to remove the slider it's very easy, guick and safe to do.

 

Wind down on the greaser to make sure there's grease in the gland & stern tube

Remove the 4 nuts on studs 

Slide the slider out to give access and clearance. You may ffind that some form wooden levers help.

Measure using chosen method, 

Replace slider and nuts

Adjust as appropriate

 

[Old Son]

Thanks all, I feel quite comfortable taking the slider out to measure the size of packing I require.

[Mike Adams]

Try to get some ptfe based packing if you can. I have found it works much better if you have worn bearings

[The Welsh Cruiser]

If you do remove the slider I hope you don't find it a bit tight, then even tighter when you try to put it back on, due to a slightly misaligned engine  

[Old Son]

On 09/11/2019 at 12:34, The Welsh Cruiser said:

If you do remove the slider I hope you don't find it a bit tight, then even tighter when you try to put it back on, due to a slightly misaligned engine  

Let's hope this wont be the case!!

[Wanderer Vagabond]

On 09/11/2019 at 11:34, Mike Adams said:

Try to get some ptfe based packing if you can. I have found it works much better if you have worn bearings

I'll be changing my packing next year when it's blacked as well and when I asked about the sizes I was advised of using PTFE based. Originally accepted the advice but when I thought about it further it occurred to me what happens should the PTFE wear off? I mean it is essentially the coating on non-stick saucepans, and a lot of the coating on some of our pans has worn off. The alternative is graphite based and whereas PTFE is a coating, graphite is a lubricant so I'm now a bit torn between the two, tending to come down on the side of graphite.

 

The other point would be that if you have worn bearings, it may be a good idea to address that problem.

[cuthound]

12 minutes ago, Wanderer Vagabond said:

I'll be changing my packing next year when it's blacked as well and when I asked about the sizes I was advised of using PTFE based. Originally accepted the advice but when I thought about it further it occurred to me what happens should the PTFE wear off? I mean it is essentially the coating on non-stick saucepans, and a lot of the coating on some of our pans has worn off. The alternative is graphite based and whereas PTFE is a coating, graphite is a lubricant so I'm now a bit torn between the two, tending to come down on the side of graphite.

 

The other point would be that if you have worn bearings, it may be a good idea to address that problem.

 

PTFE is a plastic, and thus can be moulded into many shapes, not just sprayed onnpans to give a non-stick finish.

 

It has a coefficient of friction similar to wet ice and thus is often used for bearings and gland packing.

 

https://www.fluorotec.com/materials/ptfe/what-is-ptfe/

[ditchcrawler]

2 hours ago, Wanderer Vagabond said:

I'll be changing my packing next year when it's blacked as well and when I asked about the sizes I was advised of using PTFE based. Originally accepted the advice but when I thought about it further it occurred to me what happens should the PTFE wear off? I mean it is essentially the coating on non-stick saucepans, and a lot of the coating on some of our pans has worn off. The alternative is graphite based and whereas PTFE is a coating, graphite is a lubricant so I'm now a bit torn between the two, tending to come down on the side of graphite.

 

The other point would be that if you have worn bearings, it may be a good idea to address that problem.

My ptfe packing has done 19 years so far  https://www.asap-supplies.com/propeller-drivetrain/gland-packing-and-removal-tools/prop-shaft-gland-packing/drive-force-ptfe-flax-sturntite-gland-packing-807521

Edited November 10, 2019 by ditchcrawler

[Slim]

It's like a dream to me that some years ago I read that graphite impregnated gland packing was not a good idea. Only a dream, no facts

[Old Son]

10 hours ago, ditchcrawler said:

My ptfe packing has done 19 years so far  https://www.asap-supplies.com/propeller-drivetrain/gland-packing-and-removal-tools/prop-shaft-gland-packing/drive-force-ptfe-flax-sturntite-gland-packing-807521

I'll measure mine at the weekend. 5mm sounds a little small if the sizes suggested in this topic are correct. Presumably the packing needs to fit reasonably tight?

[MoominPapa]

18 hours ago, Slim said:

It's like a dream to me that some years ago I read that graphite impregnated gland packing was not a good idea. Only a dream, no facts

It means that any grease which escapes from the gland  makes indelible black stains on anything it touches. Don't ask me how I know this.

 

MP.

 

[Tony Brooks]

1 hour ago, MoominPapa said:

It means that any grease which escapes from the gland  makes indelible black stains on anything it touches. Don't ask me how I know this.

 

MP.

 

Where is graphite on the galvanic scale compared with mild steel, stainless steel, brass and aluminium? I suspect that may explain why graphite packing might not be ideal but can't see it mattering so much in fresh water.

[Boater Sam]

1 hour ago, Tony Brooks said:

Where is graphite on the galvanic scale compared with mild steel, stainless steel, brass and aluminium? I suspect that may explain why graphite packing might not be ideal but can't see it mattering so much in fresh water.

Way up there, hence never use graphite grease on a boat, anywhere.