Stuffing box packing - When to replace?

[Mirage35]

I seem to be obsessed by the stuffing box, maybe because it's the one thing on the boat I thought I understood.


So, how do you know when it's time to replace the packing? Is it just engine hours, or age, or a combination, or something else?


I'm asking because I've had problems adjusting it this season. I try to tweak for a very slow drip while motoring, but then I'm getting more flow while at dock. But if I tighten it to not drip while docked I see no drips while using it.


It was no doubt installed when the diesel was changed: now has only 170 hours operation but is something like 8 or 10 years old. And in case it's relevant, the boat is hauled and stored over (Canadian) winter each year.


Thoughts?

[mjscottinnc]

If your prop shaft is leaking when the engine is not running by anything more then a few drops and you have no adjustment left with the packing nut, it's time to repack.


If you can not find the right tension using the packing nut between running and not running, you might want to consider smaller diameter packing.

[Mirage35]

Originally Posted by mjscottinnc

If your prop shaft is leaking when the engine is not running by anything more then a few drops and you have no adjustment left with the packing nut, it's time to repack.

Ahh, yes, but if I have adjustment left - just keep cranking it down or is there something else I should be looking for? Thanks for the input.

[mjscottinnc]

If you have adjustment use it, if not make sure you do. Just that simple.


I'm sure you know this, but I'll say it anyway. After your boat is relaunched after its winter hibernation, the packing will have dried out and leak like a sieve when its splashed. Give it a few hours or even a day or so for the packing to re-swell and seal. If you tighten it down when its dry, it will be way too tight once it swells.

[billknny]

Originally Posted by mjscottinnc

If you have adjustment use it, if not make sure you do. Just that simple.

This is wrong. It is more complex than just cranking down until there is no room to crank any further. If you just keep tightening it more and more to get it to stop leaking you can score the shaft, and it will not seal--ever again.

The traditional packing material is a woven flax impregnated with wax. If you tighten it too much the wax melts out of the flax, and damage occurs to your very expensive prop shaft..

When running, the stuffing box should never be too hot to touch. You should be able to hold your hand on it, even after running it hard and fast.

If the packing is old, it can harden (i.e., lose the wax lubricant). Tightening it too much will score the shaft. If you are having problems, replace it. If it is a real pain in the butt to replace or adjust (and too many boats are like that!) you might consider PTFE Drip-less Packing. I have used it, and it is great stuff.

[Nicholson58]

I had issues with mine. It turned out the shaft was grooved and pitted at the gland. Once repaired, it was easy to manage.

[Wotname]

Originally Posted by Nicholson58

I had issues with mine. It turned out the shaft was grooved and pitted at the gland. Once repaired, it was easy to manage.

How did you (or others) repair the shaft damage?

[rbk]

If it’s not too bad you can have it skimmed down but any pitting could be a deep crack. You could have it dyed and inspected or for 300-400 bucks for most modest sized boats you can get a new shaft. For another 250 you can add a pss or similar and never have to adjust you gland or drip water again. If you keep the gland avoid graphite seals as they can destroy your shaft.

[Jim Cate]

Originally Posted by Wotname

How did you (or others) repair the shaft damage?

One way is to weld up and re-machine. Obviously a better deal on mre expensive, large shafts. But I wonder if a Speedy Seal type repair would work with a stuffing box? They sure work well with lip seals on shafts.

Anyone ever hear of doing this?

And for the OP: I had very good results with the teflon impregnated packing and some special grease that West Marine sold me. This was back around 1985 or so... you could tighten the packing to the no-drip state and it ran cool and without damage. Had that setup until when I sold the boat in 2005... several thousand hours, original packing and grease. Good stuff!

Jim

[DumnMad]

Originally Posted by AnglaisInHull

Ahh, yes, but if I have adjustment left - just keep cranking it down or is there something else I should be looking for? Thanks for the input.

Has it got a grease nipple ?

[NYSail]

I had a traditional stuffing box on last boat and it barely dripped. When first bought boat I replaced with a new unit and packed with a Teflon packing..... I could run hard for hours with barely a drip and grab the nut.... always cool to touch. I would repack every 3 years.... why not? It is a simple process and cost little, after 8 years I removed shaft and no scoring or any problems. Also when I bought boat there was a slight score in the shaft.... the prop shop inspected shaft and all otherwise was good so they just extended the rubber hose 1/2 inch or so to set packing on a new section of shaft.

So my answer is at haul out, remove shaft, Clean stuffing box, replace rubber hose and repack with a modern packing material.

Good luck
Greg

[mjscottinnc]

Originally Posted by billknny

This is wrong. It is more complex than just cranking down until there is no room to crank any further. If you just keep tightening it more and more to get it to stop leaking you can score the shaft, and it will not seal--ever again.

The traditional packing material is a woven flax impregnated with wax. If you tighten it too much the wax melts out of the flax, and damage occurs to your very expensive prop shaft..

When running, the stuffing box should never be too hot to touch. You should be able to hold your hand on it, even after running it hard and fast.

If the packing is old, it can harden (i.e., lose the wax lubricant). Tightening it too much will score the shaft. If you are having problems, replace it. If it is a real pain in the butt to replace or adjust (and too many boats are like that!) you might consider PTFE Drip-less Packing. I have used it, and it is great stuff.

The question was when to repack the stuffing box, which implies a basic understanding of how it is supposed to work. A simple question with a simple answer.

[Nicholson58]

Originally Posted by Wotname

How did you (or others) repair the shaft damage?

There was no replacing my shaft. Nine feet long, 50 mm and hollow bored for the variable prop pitch controls. It would have been more than $20,000 to replace. I was chief engineer at a large custom machine builder at the time. I put it in our large engine lathe and turned down the packing area and also the heavily worn part at the Cutlass bearing. It was then plasma powder spray welded over sized in both places. Back in the lathe, turned and polished. My only out of pocket cost was the plasma weld, $380.

BTW, clean the marine growth out of the grooves of the Cutlass bearing with a SS bicycle spoke.

[Mirage35]

Thanks for the feedback, all.

There’s no indication of any damage and it doesn’t run hot, just getting to be a nuisance to adjust. Since I’m hauling the boat for the winter next week, I think I’ll put re-packing on the to-do list for spring.

[GrowleyMonster]

I figure on removing old packing and repacking at every haulout for whatever reason. That way if I go a few years, at least it starts out with fresh packing. I usually cut an extra ring, too, seal in plastic and zip tie somewhere near the stuffing box. It is pretty simple to add the ring when needed, even with the boat in the water.

If you don't overtighten, and the shaft is not scored, the packing should be good for about 5 years and "sorta" good for a lot longer. But it is cheap and easy to replace, so doesn't make sense to put it off any longer, or to not take the opportunity to replace it all when on the hard. Ideally, that spare ring of packing will never be needed.


And don't forget, you probably have another stuffing box in your lazarette, if you have wheel and quadrant steering. That's a whole different critter and you can't count on water for lubrication and cooling, so don't overrtighten.