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How to tell the size of gland packing


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Planning to renew the gland packing on prop and realise I need to be well prepared.but how do I know what size packing so buy before dismantling and measuring it?

Have looked at previous threads and feel confident as to how to do it but seems there are 3 different sizes.

 

Never done this before so this may come over as a dumb question - but then not my first.closedeyes.gif

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Planning to renew the gland packing on prop and realise I need to be well prepared.but how do I know what size packing so buy before dismantling and measuring it?

Have looked at previous threads and feel confident as to how to do it but seems there are 3 different sizes.

 

Never done this before so this may come over as a dumb question - but then not my first.closedeyes.gif

 

Measure the outside diameter of the packing follower, then the diameter of the shaft and deduct that from the OD of the follower. Halve the difference, and that's the packing size.

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Measure the outside diameter of the packing follower, then the diameter of the shaft and deduct that from the OD of the follower. Halve the difference, and that's the packing size.

 

That's how I did it. I used a vernier caliper for accuracy. Trying to measure up by lining a rule up by eye was always going to be fraught with inaccuracy

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The packing follower is the tube the shaft goes into- the thing with a flange and two nuts at the front end. It pushes the rings of packing into place and lightly compresses them onto the shaft and into the stern tube itself.

 

The OD of the follower is the same as the inside diameter of the stern tube which the packing fits into so that the OD of the follower gives you the OD of one ring of packing. As Tony D says, the ID of the ring of packing is the diameter of the shaft since the packing rubs gently against the shaft.

 

N

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Is the packing follower the tube that the shaft goes through and if so why do you measure the outside diameter?

The packing follower or pusher is part of the shaft top bearing. It's all part of the flange casting that the threaded studs poke through with the adjusting nuts on the outside. . The inner inch or two of this unit slides accurately into the tube to push on the packing. So the difference between the outside diameter of this pusher unit and the outside diameter of the prop shaft is the thickness of the packing required. 5/16''sq packing is a popular size for an 1.1/2'' shaft..

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The packing follower or pusher is part of the shaft top bearing. It's all part of the flange casting that the threaded studs poke through with the adjusting nuts on the outside. . The inner inch or two of this unit slides accurately into the tube to push on the packing. So the difference between the outside diameter of this pusher unit and the outside diameter of the prop shaft is the thickness of the packing required. 5/16''sq packing is a popular size for an 1.1/2'' shaft..

 

It's half of the difference for the packing size, Bizz. I know what you mean, but if he goes by the difference in diameters he'll be buying 5/8'' packing.

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In this image I pinched off the net, the "packing follower" in Tony's post is shown as "packing gland", and the "packing rings" are what you are intending to replace. Just ignore the fact that this diagram shows the shaft diameter as larger inside the stern tube than outside it.

 

 

 

 

14075_127_1.jpg

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Provided you can get the joint apart far enough to put a twist drill shank it, David's method is a doddle, and involves no measuring.

 

But if there isn't lots of free shaft to allow you to get the joint apart enough to get the drills in, you'll need to use the measure two diameters and halve the difference approach.

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In this image I pinched off the net, the "packing follower" in Tony's post is shown as "packing gland", and the "packing rings" are what you are intending to replace. Just ignore the fact that this diagram shows the shaft diameter as larger inside the stern tube than outside it.

 

 

 

 

14075_127_1.jpg

Good diagram.

Where does the stern tube grease get injected? To the left or right or the centre of the packing, as you look at the diagram? Is that the "water service"?

I get a lot of grease exuding through the packing gland as if it gets injected to the right side.

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And halfway between the two. I bought 5/16 packing last autumn

The most common for 1.1/2'' shafts.

 

Whatever the size is, oversize packing must not be forced in, it will be too tight and will overheat and jambe the shaft.

Edited by bizzard
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The most common for 1.1/2'' shafts.

 

Whatever the size is, oversize packing must not be forced in, it will be too tight and will overheat and jambe the shaft.

 

OTOH it's perfectly normal for the 'correct' size of packing to be too tight to slip into the space, it can be hammered to make it a little thinner after which it will slip in easily.

 

Tim

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OTOH it's perfectly normal for the 'correct' size of packing to be too tight to slip into the space, it can be hammered to make it a little thinner after which it will slip in easily.

 

Tim

Quite Tim, the correct size. I meant forcing say 3/8'' in in place of 5/16''.We had someone here who did this a couple of years ago, he wrecked the drive plate and burnt the gearbox out. It took me about 3hours to free the shaft. He wanted a new gearbox which I fitted, a PRM 150. RLWP had the old one.

Edited by bizzard
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There are only a few sizes of packing commonly available. e.g. 6mm or ¼", 10mm or 3/8" will compress/expand to fill the gap.

 

Alan

 

We had completely the opposite experienced some time back when an engineer used 6mm (1/4") packing which he had hammered down in a gland designed forv8mm (5/16").

 

It leaked incessantly despite constant adjustment. I think you have far greater chances of success by using the correct size in the first place.

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One other point from way back in my apprentice days it was recommended to use 3 rings of packing, the ends to be cut at 45 degrees making a scarf type finish to the ring ends & the ends of each ring be placed at 20past, 20to, & 12oclock or 1/3 of the circumference apart. from past experiences if the ends are spaced apart & the packing rings cut 2mm or so long a clean square cut end works fine.

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Planning to renew the gland packing on prop and realise I need to be well prepared.but how do I know what size packing so buy before dismantling and measuring it?

Have looked at previous threads and feel confident as to how to do it but seems there are 3 different sizes.

 

Never done this before so this may come over as a dumb question - but then not my first.closedeyes.gif

Its only about a fiver for a half metre length, so if you can't measure accurately before dismantling, buy a selection - not as if it will break the bank!

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One other point from way back in my apprentice days it was recommended to use 3 rings of packing, the ends to be cut at 45 degrees making a scarf type finish to the ring ends & the ends of each ring be placed at 20past, 20to, & 12oclock or 1/3 of the circumference apart. from past experiences if the ends are spaced apart & the packing rings cut 2mm or so long a clean square cut end works fine.

BUT don't assume that you'll only need 3 rings. I needed 7!!! (The diagram shows 5). Buy enough just in case because if you find that you haven't got sufficient you'll be inconvenienced waiting for another delivery.

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BUT don't assume that you'll only need 3 rings. I needed 7!!! (The diagram shows 5). Buy enough just in case because if you find that you haven't got sufficient you'll be inconvenienced waiting for another delivery.

 

Most modern nb sterngear does only take 3 or 4 rings. Older working boat type sterngear often took a lot more (of much thicker packing).

 

Tim

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