New Stuffing Box Nuts?

Hello! We need to replace the stuffing box nuts on Calypso, a 1977 Marine Trader; See attached photos. Does anyone know if there is a particular thread and type of nut? Thank you!

Greetings,
Mr. C. My best guess would be a metric nut of no special alloy although SS would be best. You can probably take a nut to Fastenal, for example and get a match up. I would suggest double nuts on reassembly, locking one against the other.

thanks! ...I tried the standard and it was not right. I'll try metric and let you know...

Can you put a C-clamp on it and remove the nut and maybe the bolt. One side may hold it together at the dock while you get to a store right size also.

Measure diameter with ruler, preferably a 6" stainless one.
Measure thread with a thread gauge. (Metric & SAE)
Both available at Amazon or any auto parts store.

It could be the angle the camera was that but that bolt looks stressed, or bent. Better to replace both. If it is a stud and not a bolt, it should screw right out, if it is a bolt , a tap with a hammer should knock it loose.

I really would not worry about water intrusion, even if you remove both bolts at the same time, providing you don't forget to replace them and run the engine.

pete

Is a new shaft on the list also?
Silicon bronze on the nuts.

Might be British Standard thread.

Mine was ordered from a guy in NY who imports MG car parts and only charged a few dollars shipping. Not at home so no contact info.

On mine an SAE would fit for about 3 turns then jamb.

All the long bolts and threaded rod on my Albin is this stuff as it was common over in Taiwan kn the 80s I have heard. Though I believe my rods are stainless.

If I had to redo ..I would just retap for SAE rod and nuts.

Pete Meisinger said:

It could be the angle the camera was that but that bolt looks stressed, or bent. Better to replace both. If it is a stud and not a bolt, it should screw right out, if it is a bolt , a tap with a hammer should knock it loose. pete

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Looking at pic 1 the plate seems to have "a thread`s width" bend to it. Maybe it`s intended, maybe not.

Personally I'd change the whole stuffing box for a PSS seal. Once fitted just a periodic check, no marking on the shaft/greasing/tightening. I've had one now for about 8 years with the boat in constant use and no problems. I fitted mine while the boat was in the water but you need to be a calm and competent DIY'er.
Just my 2 pence worth.

1/2”-13 just a guess. Let me know if I’m close.
What’s wrong with the existing nuts?

Should really be double nutted. As for thread, are there any original stuffing boxes left? The Fastenal suggestion is the best I've heard.

On my boat the stuffing box (1983) is original. Why double nut? Those nuts have lots of back pressure and won't back off. Even if both loosened there would not be a catastrophic leak.

WayneDana2 said:

Should really be double nutted. As for thread, are there any original stuffing boxes left? The Fastenal suggestion is the best I've heard.

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I recently replaced mine. They were BSW 1/2-12.

catalinajack said:

On my boat the stuffing box (1983) is original. Why double nut? Those nuts have lots of back pressure and won't back off. Even if both loosened there would not be a catastrophic leak.

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My stuffing box looks like that and it has double nuts on it.

525cj said:

I recently replaced mine. They were BSW 1/2-12.
View attachment 98882

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That's where I got mine...as someone before me was nice enough to provide the info when I had trouble identifying the correct nut size.


We will see how this plays out...hope the OP posts what his solution was.


As far as double nutting...a good idea but probably overrated in this situation. The packing probably acts somewhat like a locknut by providing back pressure for awhile...and even then as posted....any loosening is not a catastrophic issue.

Thank-you everyone -it is a 1/2-12 inch standard. I also need to add 2-3 layers of flax. Does anyone know the correct size? It's a 77 Marine Trader 40DC

Diver Dave: You say it should be silicon bronze nuts and not Stainless?
THANK YOU!

I won’t say imperative. But the entire assy is a bronze alloy. Putting steel in the mix is not necessary for strength or availability. SiBr does not suffer from crevice corrosion or galvanic corrosion when near copper and seawater.

Damn, my guess of 1/2 -13 was pretty close!

Caribe said:

Thank-you everyone -it is a 1/2-12 inch standard. I also need to add 2-3 layers of flax. Does anyone know the correct size? It's a 77 Marine Trader 40DC

Diver Dave: You say it should be silicon bronze nuts and not Stainless?
THANK YOU!

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Sounds like the British Standard thread, copied by others.

For the packing I would recommend you go to an industrial plumbers merchant and ask for 1/4'' PTFE steam packing. Its a small roll of square woven material impregnated with PTFE.
After extracting all the old packing (use a bit of gas welding rod with a sharpened end turned to make a hook to pick it out) then cut the new packing into short lengths which form a circle around your shaft with an offset join.
Cut the packing at an angle so that the 2 faces form a continuous circle around the shaft, lightly oil the shaft and slide a circle of packing down into the stuffing box, tap lightly into place until its just firm.
Slide the next circle down with the joins offset by 180 degrees, the next by 90 degrees etc so that no 2 joins are together until you have sufficient packing in place. Grease liberally.
Tighten the bolts until just lightly firm, then run the boat in gear and check the stuffing box, gently tighten each nut equally, one drip from the stuffing box roughly every 20/30 seconds when running is fine.
Check regularly.
Some people have been known to tighten them so tight and don't bother greasing them that they run hot and will wear a groove on the shaft. (my boats PO). = $$$$$$$$

I think this is likely right. The OPs setup looks like mine and it requires BSW-1/2

525cj said:

I recently replaced mine. They were BSW 1/2-12.
View attachment 98882

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The 1/2-12 used to be a common size on domestic machinery. I ran into it only a very few times on old machinery. Old even when I was much younger.

I don't remember when but the standards were changed to the 13 TPI. The change was done a long time ago.

The Whitworth thread was another complication as the pitches often matched domestic but the thread included angle was slightly different at 55° instead of 60°.



I agree about the old bronze nuts. They were very likely made of the same bronze as the stuffing box itself meaning another 40 yrs. unless they have been damaged.
Good marine bronze will out last most other materials. The catch is do you have good marine bronze? I'd say you do since the parts are already 30+ yrs.


Just a last note. Hack up an old, small fender and once you are satisfied with the stuffing box adjustment use that fender to fashion a cover over the entry of the shaft into the box. Rig it so the split is down and the very fine mist will be caught and will then drop into the bilge. Otherwise that mist will travel far causing rust on any nearby steel parts.
Secure the fender cover with a worm gear clamp lightly or a Tyrap. Then it can be easily removed for adjustments. Does not have to be pretty.

09.2022

Recently had to replace the Studs on my 73' Marine Trader stuffing box and 1/2"-13 was the stud size. Electrolysis, was bad so when anyone replaces there Studs take a tread cleaner and clean the threads on both the studs and the stuffing box threads. Tried 1/2" and it would work until i cleaned those threads up really good.