Servicing stern gland

[ghostlymoron]

I've recently acquired a new (to me) 19' boat complete with MD1 engine a the usual old boat drive system. When I viewed her before purchase the stern gland was dripping even when the engine wasn't running so it obviously needs some attention. The arrangement is as shown on Cox Engineering website http://coxengineering.sharepoint.com/siteimages/packing1.JPG and appears in good condition. The gland nut is slightly unusual as it is tightened by a C spanner rather than a conventional hex spanner (but water pump pliers do the trick).
I've decided to renew the packing rather than just nip it up a bit. Am I right in thinking that I will find the old packing (and insert the new) inside the gland nut? I think the shaft dia is 1" so I shall measure the inside dia of the gland nut, deduct shaft dia, divide by two and order the appropriate size of packing from ASAP.
Good plan?

 

[Spyro]

Sounds about right. Yes the packing is in the nut. Good info here
http://www.tb-training.co.uk/10sgear.htm#bmn30

 

[vyv_cox]

The shortest that ASAP sell is 1 metre, which will do yours several times over. You need to know what size, probably 6 mm but best to measure.

As my site says, there are various designs. In some cases the packing may be inside the nut but in others there is an internal part that pushes the packing down inside the cylindrical part. I believe the second photo shown, on the right on the first line, is like yours. It looks like the type with the packing inside the cap.

 

[ghostlymoron]

'I believe the second photo shown, on the right on the first line, is like yours. It looks like the type with the packing inside the cap.' http://coxengineering.sharepoint.com/siteimages/DSCN1630.JPG
Yes mine looks very like that one except it doesn't have the rubber tube.

 

[ghostlymoron]

I've now unscrewed the gland nut and measured the shaft and nut I/D. Shaft is 1" and nut I/D is 34mm (excuse mixed units) so what size packing do I need?
I've poked around inside the gland nut with a little screw driver and I can't find any old packing! Perhaps previous owner relied on grease alone to keep the water out - no wonder it leaked. (Boat has been on the Broads previously).

 

[vyv_cox]

I've now unscrewed the gland nut and measured the shaft and nut I/D. Shaft is 1" and nut I/D is 34mm (excuse mixed units) so what size packing do I need?

Half the difference between the two, so 34 - 25 = 9 which gives 4.5 mm. ASAP do 5 mm which will be fine for the job, just hammer it a little to reduce the thickness before fitting.

 

[JSYmartini]

Is it safe to repack a stern gland in between tides? I know there is no right or wrong answer to this one but what do most people do? Or what did most people do before travel hoists were invented?

The previous owner of my boat said he would always get a lift out but he used to get lifted out every winter for anti foul etc. The difference is his salary is 7 or 8 times mine!

 

[NormanS]

Is it safe to repack a stern gland in between tides? I know there is no right or wrong answer to this one but what do most people do? Or what did most people do before travel hoists were invented?

The previous owner of my boat said he would always get a lift out but he used to get lifted out every winter for anti foul etc. The difference is his salary is 7 or 8 times mine!

You should have no problem repacking a gland between tides, assuming you mean being dried out.

 

[vyv_cox]

I recently did mine on the water, not for the first time. If you prepare at least one turn of the new packing beforehand, ready to push into the gland, it is surprising how little water comes in. In most cases water only comes in at any rate when the last turn of the old packing is withdrawn, easily taken care of with your bilge pump.

My recent repacking job was far from straightforward because some daft previous owner had put in short lengths of packing far too small for the aperture. It took me ages to pull all this out because access is very restricted. Despite that my automatic bilge pump did not operate throughout, giving some idea of the amount of water that gets in. Wrapping a rag around the stern gland pretty much stops all flow if you need a break for any reason.

 

[NormanS]

I recently did mine on the water, not for the first time. If you prepare at least one turn of the new packing beforehand, ready to push into the gland, it is surprising how little water comes in. In most cases water only comes in at any rate when the last turn of the old packing is withdrawn, easily taken care of with your bilge pump.

My recent repacking job was far from straightforward because some daft previous owner had put in short lengths of packing far too small for the aperture. It took me ages to pull all this out because access is very restricted. Despite that my automatic bilge pump did not operate throughout, giving some idea of the amount of water that gets in. Wrapping a rag around the stern gland pretty much stops all flow if you need a break for any reason.

It actually makes it easier to get the old packing out, when there is a little water pressure from the sea.

 

[JSYmartini]

I was talking about do it whilst dried out, doing it in the water sounds perfect for someone who thrives under pressure! Although it seems water ingress isn't what I thought it would be.

Hopefully getting a lift out next winter so I can swap them for PSS seals.

 

[ghostlymoron]

Replacing a good gland packed device with a PSS is completely unnecessary imo unless you've got a high revving engine. The advantages of the former are that they are cheap, easily maintainable and can't give a catastropic failure. Disadvantage is that you'll usually have the occasional drip.