Propshaft seal/Stuffing box

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Nasher

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Down South near Pompey
www.simonnash.co.uk
Hello all.

I'm working on a project at the moment and have come up against a small hurdle.

The boat has a small inboard engine with a sterntube and propshaft.

I need a stuffing box or modern rotating seal type replacement, but am struggling with it being so small.

The propshaft Diameter is only 5/8in and the sterntube only 1,3/64in.
All the ranges I can find at my end of the cost scale start at 3/4in propshaft diameter.

Does anyone have anything hanging around or have any suggestions?

My next move as usual will be to fire up the lathe and make one from scratch, but I'll need some Bars of Brass/Bronze/Ali.

I'm also going to need a 5/8 to 5/8 flexible coupling to join the propshaft to the engine.

Thanks

Nasher.
 

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Don't think there is anything commercially available that small. as you have found you can get conventional stuffing boxes down to 3/4" but modern seals don't go smaller than 1"/25mm. You might try Lake Engineering in Poole to see if they have any ideas.
 
My Macwester had a narrow shaft, not quite as small as yours IIRC.

It was identified here as Stuart Turner gear, and it was possible to get a phenolic cutless and new packing OK. Lakes/ASAP

Still going strong for the new owner as far as I know.
 
NickRobinson said:
My Macwester had a narrow shaft, not quite as small as yours IIRC.

It was identified here as Stuart Turner gear, and it was possible to get a phenolic cutless and new packing OK. Lakes/ASAP

Still going strong for the new owner as far as I know.
Click to expand...

The smallest ST stern gear is (I think) 3/4" which was used with the 1.5hp engine - 7/8" with the 5hp and 1" with the 8/10hp. Other builders also used the stern gear. The outer bearing was rubber, but you can now get a housing converted to use a normal cutless bearing
 
Thanks for the input guys.

My thoughts at the moment are to go for something @1in, and turn up a sealable sleeve to go over the propshaft in the right place. The other end should be easier sealing a rubber hose down onto the tube with some form of rubber insert or spacer.

Nasher
 
Think outside the conventional. You have a lathe, so here is my idea. Volvo shaft seals and the similar but cheaper Eliche Radice seals from Sillette are available in 25mm bore x 39mm stern tube size. Too big - No problem, as I will explain. But first why do you need a flexible coupling? I do without one and so do many others. If your engine mounts are OK (not too wobbly) and the alignment is good then no flexible coupling should be needed.

So here is what I would do. Scroll down the page to look at the smallest RMTA shaft seal here http://www.sillette.co.uk/price_pdf_files/tides_marine_shaft_seals.pdf
Get a piece of 25mm polished stainless steel shafting and machine a coupling to fit both it and your gearbox flange. Bore the 25mm shaft to 5/8 inch and fit a key into it and the shaft. Opposite the key you need a deep dimple in the shaft to take a setscrew which should pass right through your new flange and the 25mm part. If the shaft is too short you may have to fit the new part with a blind bore and a key plus an axial Allen screw. You also need to machine up a sleeve to fit the existing sterntube and take the 39mm internal diameter of the seal. Just fit the sleeve in place with engineering adhesive. Make a properly dimensioned drawing of the parts first, to ensure that the seal bears on the new 25mm part clear of the setscrew hole.
 
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Just a thought ............. if you have the skills to machine the propshaft to suit the existing stern tube then it doesn't have to be the same diameter all the way along. Leave the coupling / stuffing box part at 3/4, machine the tail end down to 5/8. All the inboard stuff is then standard 3/4 stock. Flexi tube might be a complication but depends on the OD of the original stern tube. M
 
All good suggestions guys, as mentioned above I am probably going to have to machine something up, so it would make sense to incorporate the coupling.

The propshaft is already in place and in very good condition, so I'm inclined to sleeve it rather than start from scratch, especially as it's the original in a historic boat.

I'll do a thread very soon with some more details of the boat itself, which is very interesting.

Nasher.
 
Another thought. If you do as I suggest just make sure that the 25mm section will pass through the stern tube if you ever need to take the shaft out. Otherwise make sure that you can free the shaft from it if needed.
 
Good point.

If I go down the route of making the inboard part of the propshaft a larger diameter it will have to be with a removable sleeve because there isn’t room inside the boat to withdraw the shaft, so it has to be inserted from outside. The bearings in the tube are also very thin wall, so wouldn't give me much more to play with if I take them out first. I do want to keep the current original shaft if possible as well.

I can easily turn up a sleeve that’s a sliding fit on the propshaft and has recesses either end to pop some lip seals in to stop any water finding it’s way up the sides.

I believe I will need a flexible coupling of some sort as any slight misalignment is going to be very hard to establish and ‘shim’ out.
Bearing in mind the engine is small capacity 2-stroke of @4HP, a couple of three fingered flanges bolted either side of a thick reinforced rubber disc will sort it out. If designed heavily enough it will also handle the thrust being transmitted through it.
The detail of the original flexible coupling is hidden in all the images I have of the original installation, and had been stripped out like the stern gland before I got hold of it.

I won’t be anywhere near the boat until the weekend, but will get some images of engine compartment and engine/gearbox so everyone can see what I’m up against.

Thanks

Nasher.
 
I like Norman E's idea of a sleeve to bring the bearing surface up to 25mm to take a Radice seal. If the sleeve was long enough it could be both a bearing for the seals and allow the fitting of a Bullflex coupling with a standard 25mm bore. The advantage of a Bullflex apart from tolerating some misalignment is that you can use an adaptor flange to mate with your gearbox flange. The only drawback with this set up is overall length - ie the space between the stern tube and the gearbox of around 220mm to allow aome clear space between the seal and the coupling. The Radice seal is the shortest of the commercially available seals at 110mm and the Bullflex is 85mm plus 15mm for an adaptor. You can get details of the coupling in the Vetus catalogue.
 
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