Repacking Stuffing Box

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Dream Quest

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Joined
Apr 25, 2012
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5
Location
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I have a 1999 Mainship 390 which has I believe a 1 3/4" propeller shaft. I am running out of adjustment on the stuffing box which has an adjustment nut on each side of the box, the boat is in the water and I have several questions:
1. Is 1/2" packing the size called for?
2. Would GFO packing be a good choice?
3. Can I get by temporarily, that is until I haul her out in a year or two, with adding a new ring of packing without removing the old?
 
I saw a video stating you can do it by putting plumber putty on the outside but you have to get in the water. Or you can put a rag over the shaft and try to do it quickly.
 
I don’t know about what size you need but my shafts are 2” and take 3/8” packing. You could pull the plate off and see what size drill bit will fit in between the shaft and the log. I suspect it will be a bit less than 3/8”.
 
A stuffing box should not just be blindly tightened and if your running out of room, that makes me a bit uneasy. Pulling out stuffing and replacing is usually an easy job, safely accomplished in the water. If you run into issues, just stuff a little anything in there while you go to the chandler or hardware store. A rag, some paper towels. If the shaft is not turning, just about anything is going to work.

Best to get new packing in there. Come prepared with a couple corkscrew tools. If the packing is baked and hardened from being overtightened, it can be a bit crispy to pull out and it is possible to break a tool. Packing that is old and not hardened will usually come out quite easily. Another hint, if you guess wrong at the perfect packing size, just massage it with a mallet/hammer gently to make it a little thicker, or thinner. You can make any close size work and it will simply cause the overall depth to change just a bit.

I’m not at all a fan of adding a new ring to old packing.

Personally, I prefer gfo.

If you have troubles getting new packing to seal without over-tightening, then inspect the shaft for scoring. That’s a real possibility resulting from prior over tightening. If the shaft is in good shape, and you put in the new rings at the right shape and size, you should tighten gently at first and creep up on the right adjustment slowly while running a little at a time. If you are starting to get tight and not seeing obvious reduction in dripping, instead of continuing to get tighter and tighter, check whether the shaft is wobbling and the running gear needs alignment. You won’t be able to get a stuffing box to perform right unless the running gear is in alignment and otherwise good shape. This ultimately is what often leads to over tightening and baked packing.
 
Just add more packing rings.
Prepare the packing material by wrapping it around the shaft, cutting it to the proper length.
Perhaps 3 rings.
Back the packing gland, moving it down the shaft, away from the prop. Add one new ring at a time, tighten the packing gland pushing the new ring in. Start the engine, rotate the shaft slowly. Do the same with the 2nd ring and maybe the third ring.... Each ring is pushed on the with the packing gland.
Dont worry about a vast amount of water, it wont happen.
After adding all the necessary packing, take the boat for a ride, making the final adjustment while underway. It is supposed to leak a drop or 3 to keep the packing material cool.
If you are unsure of yourself, seek help from another boater. It is simpler and less scary than one may fear.
IF I recall correctly, the packing gland should be in about 1/3 of the total distance.
 
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Packing box

ghost said:
A stuffing box should not just be blindly tightened and if your running out of room, that makes me a bit uneasy. Pulling out stuffing and replacing is usually an easy job, safely accomplished in the water. If you run into issues, just stuff a little anything in there while you go to the chandler or hardware store. A rag, some paper towels. If the shaft is not turning, just about anything is going to work.

Best to get new packing in there. Come prepared with a couple corkscrew tools. If the packing is baked and hardened from being overtightened, it can be a bit crispy to pull out and it is possible to break a tool. Packing that is old and not hardened will usually come out quite easily. Another hint, if you guess wrong at the perfect packing size, just massage it with a mallet/hammer gently to make it a little thicker, or thinner. You can make any close size work and it will simply cause the overall depth to change just a bit.

I’m not at all a fan of adding a new ring to old packing.

Personally, I prefer gfo.

If you have troubles getting new packing to seal without over-tightening, then inspect the shaft for scoring. That’s a real possibility resulting from prior over tightening. If the shaft is in good shape, and you put in the new rings at the right shape and size, you should tighten gently at first and creep up on the right adjustment slowly while running a little at a time. If you are starting to get tight and not seeing obvious reduction in dripping, instead of continuing to get tighter and tighter, check whether the shaft is wobbling and the running gear needs alignment. You won’t be able to get a stuffing box to perform right unless the running gear is in alignment and otherwise good shape. This ultimately is what often leads to over tightening and baked packing.
Click to expand...

I think what Ghost stated is correct. If after repack ing and it still leaks much, the the shalf might not be too straight due to gear alignment. Gears go through pressure and heats that overtime can be out of alignment which leads to shalf not spinning straight which leads to leads to more water entering.
 
Also, the shaft could be scored if you have been tightening it willy nilly.
 
DO NOT use carbon shaft seal. It is for pumps etc and will destroy your shaft log or the shaft.
 
Mainshiptom said:
My Own Mainship 350 is leaking now when prop not turning which size packing should i get?
Click to expand...

My 1999 350 has a dripless. Interesting that they released both a 350 and a 390 in 1999. Mine must have been released EARLY in 1999, prior to the model name change.
 
Mainshiptom said:
My Own Mainship 350 is leaking now when prop not turning which size packing should i get?
Click to expand...


Have you tried tightening the gland nut a turn or so. Thats its function!!! Every so often as wear takes out packing you just tighten the net a bit till it just stops....but dont tighten it down too tight, its not a bolt, or you could score the shaft!!!!
 
which size should i get?

jimisbell said:
Have you tried tightening the gland nut a turn or so. Thats its function!!! Every so often as wear takes out packing you just tighten the net a bit till it just stops....but dont tighten it down too tight, its not a bolt, or you could score the shaft!!!!
Click to expand...

Thanks for the advice , I did tightened the screws and leak has stopped but i would like to have new packing on board and would be interested if anyone can advise on size? i have a single caterpillar 3116
 
350/390

Shrew said:
My 1999 350 has a dripless. Interesting that they released both a 350 and a 390 in 1999. Mine must have been released EARLY in 1999, prior to the model name change.
Click to expand...

Maybe mine is a 390? or a 350 how do I find out? in the HIN number?

There is no where to say what boat it is?
 
I would not change boats just for the stuffing box, its cheaply changed. BUT, and this will cause some discussion, I prefer a stuffing box to a dripless any day as my neighbor almost lost his boat with a dripless that got some sea weed in it.
 
Dream Quest said:
I have a 1999 Mainship 390 which has I believe a 1 3/4" propeller shaft. I am running out of adjustment on the stuffing box which has an adjustment nut on each side of the box, the boat is in the water and I have several questions:
1. Is 1/2" packing the size called for?
2. Would GFO packing be a good choice?
3. Can I get by temporarily, that is until I haul her out in a year or two, with adding a new ring of packing without removing the old?
Click to expand...

Just done mine so its a single shaft and I used 1/4" packing
 
I have never removed old packing. Just keep adding more for years. Usually 2 or three rings. I dont know where the old goes and I dont care......probably where the elephants go to die and where all the short stubby pencils and short pieces of solder go.
 
The size of packing material is determined by measuring the outside diameter of the shaft and the inside diameter of the stuffing box and dividing the difference by two. Your local yard should be able to verify this for you. Don't guess the size or just measure the shaft because you may not have the same brand name stuffing box as another boat with the same shaft size.
 
Eagle Pursuit said:
The size of packing material is determined by measuring the outside diameter of the shaft and the inside diameter of the stuffing box and dividing the difference by two. Your local yard should be able to verify this for you. Don't guess the size or just measure the shaft because you may not have the same brand name stuffing box as another boat with the same shaft size.
Click to expand...

I agree 100%
 
Probably a dumb question

When someone says to adjust underway....you don’t mean with the shaft spinning do you? I would assume you tighten...put in gear for a bit, take out of gear, then re-tighten if needed. Is that correct?
 
DO NOT...I repeat DO NOT try to adjust it while the shaft is spinning. That is a good way to kill yourself or lose a body part. Who said you should adjust it underway? They are NUTS, I said replace the stuffing IN THE WATER, NOT UNDERWAY. You cannot work on a spinning shaft that has 150 HP driving it unless you have a death wish.
 
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I've often ended up adjusting it, taking it out for a sea trial, shutting down the engine, fine tuning it, restarting and re-evaluating, and repeating as necessary.

The packing seems to need to run to break in. And, I have a tendency to set it too loose at the slip. So, by running it, I get to break it in and see how much it drips at cruise.

I wouldnt want to loosen the lock nut underway for fear that it'll loosen up and, when I go to adjust it, I'll keep losing my reference.

Regardless, I think the person giving that advice was likely talking about an fine tuning adjustment after a test run, or with engine off between segments of a test run.

Cheers!
-Greg
 
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That’s what I thought

Hahaha, thanks for the replies. I am a fireman and immediately thought making the adjustment while under way was a sure fire way to end up in the ER.
 
Whilst in the US Navy, we were told to tighten when we had docked for a period of time (undefined) and loosen it prior to getting underway.
Was it done? Daymned if I know. I was in the engine room.
 
I'll go inform every millwright and industrial mechanic I've ever worked with that they are doing it wrong.

But you have a point. If you are not comfortable with doing this, then don't.
jimisbell said:
DO NOT...I repeat DO NOT try to adjust it while the shaft is spinning. That is a good way to kill yourself or lose a body part. Who said you should adjust it underway? They are NUTS, I said replace the stuffing IN THE WATER, NOT UNDERWAY. You cannot work on a spinning shaft that has 150 HP driving it unless you have a death wish.
Click to expand...
 
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Wanna-b said:
When someone says to adjust underway....you don’t mean with the shaft spinning do you? I would assume you tighten...put in gear for a bit, take out of gear, then re-tighten if needed. Is that correct?
Click to expand...

Not reallly....one must realize working around moving parts has it's dangers, but on mant boats no big deal..

You just have to make that call, but adjusting a few fittings while the shaft is turning can be daunting or no big deal.
 
IF you insist on adjusting the shaft packing glad while the shaft is turning, remove all loose fitting clothing and I recommend, you do not undertake this without someone watching you.
 
Personally, I tend to adjust mine with the shaft just freewheeling slowly (engine being adjusted in neutral, other engine idling in gear to maintain steerage). Although I have done it idling in gear as well. Never above idle and in my case, the stuffing boxes aren't in my engine room, they're behind the bulkhead. So they're both accessed from floor hatches directly above them making it pretty easy to safely reach in there and adjust without getting caught up in moving parts (no spinning coupler bolts nearby to snag on, for example).
 
Of all the dangerous things we do in boating, never thought tightening stuffing boxes as up there...be careful but not paranoid.
 
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