Overgreased stuffing box? Remedy?

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Arctic Fox

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Hi,

I am looking for some advice and guidance around the age old 'hot stuffing box issue. I think I know the reason but the more input the better, I think!

The problem is......I have recently re engined with a small Diesel. The engine was installed and lined up by a qualified engineer. I however, packed the stuffing box and tightened the packing nut etc. I did this as per the accepted methodology. I ran trials on Saturday but ended up with the 'Hot box'. By hot I mean I can hold it more or less indefinately but it wouldn't take that much to make it uncomfortable to hold. A summary of the pertinent facts are...

The shaft turns freely and windmills when knocked out of gear
There appears to be no excess vibration
The stainless shaft does not feel hot where it exits the tube
I get no water drips - even when the packing nut is slackened right off
There is not much heat @1000 rpm when just in gear - I happily motored round the harbour at this speed for 20+ minutes with no heat noticable
Heat appears at higher revs (2700/3000 rpm)

Now an admission (which might provide an easy answer)....In my naivity I thought 'grease is good' so when everything was in place I gave the stern tube / stuffing box a right good greasing via the lubricator. I now realise that this is not the smartest thing I might have done so.....

Do you think this is the reason for the heat or is something more sinister going on?
Will it damage the shaft/box if I run like this?
How can I solve the problem if it is the grease?

Thanks in advance and all advice will be greatfully received

Cheers

AF
 
My opinion as a boatowner who does his own maintenance, not a mechanic.
The new packing is just bedding in.
Plenty of grease will not harm it.
If you can touch the metal it is not doing any damage.
My procedure after repacking was to screw up quite tightly, grease well and run for a while then adjust again, I liked to have it so that I got about one drop of water every 10 - 30 secs. or so when running hard but none when stopped. If I got it to run cool and never drip at all it was a fluke. I kept putting grease through every few hours running and always liked it to have plenty in there, this reduced the drip frequency further. I have always felt safer with an occasional drip than with a hot box.
I think your problem (if you have one) will soon be ok.
 
Hi Quandary,

Thanks for the reply....I can certainly hold the metal although it is hot. I must admit to be puzzled over this though. Anyway, I will give her a few more runs and see what happens!

Thanks again

AF
 
Surprised that you have not had more replies, you usually get dozens for this type of query, but give it a bit more time
 
Give it bit longer it can take a good few hours to get it just right. If it gets too hot the grease will melt and run out before the packing starts burning.
 
I'm happy that if it spins when you're sailing, it can't be too tight.
Mine kicks in somewhere near 4 knots under sail, and doesn't get hot when motoring, but then I don't tend to do more than 1500 engine revs ( 500 shaft) under power.
 
The heat is because of the grease, but you probably don't need to worry as it seems many people love the idea of lots of grease in the gland and they get by.

What it does (to a greater extent) on larger vessels where the shaft surface speed may be higher is cause shaft scoring which then degrades the sealing surface. The aim is to keep the shaft cool and lubricaed and water is still the best thing for the job, even the most advanced packing such as Duramax Ultra X relies on a small ammount of water (not grease) to help lubricate and cool. Grease is a poor conductor of heat and a shaft that heats up and then cools down will never have a great seal as it will change its diameter in what is a fixed diameter packing.

I think I'm outnumbered here but I believe a well packed and adjusted water only system is the best way to keep a good sealing surface on the shaft, and a stable shaft temperature and hence less dripping.
 
Thanks for the replies,
I wish I hadn't been so ignorant but I genuinely believed grease was good.....I will continue to run things and hopefully things will settle down or at season end I will clean it all out again. Appreciate the reassurances that I am not destroying the lovely stainless shaft!:)
 
We turn our greaser one half turn before sail/motoring and once before leaving the boat for any length of time. Very little dripping of water when static, not a lot when finished motoring either. We once used a different grease in error and it became liquidised, and no good as sealant, the change appeared to be because of pressure applied on the greaser rather than a heating reason, but we changed to the proper grease(Keenol?). Not sure if they are still in business so will need to find another alternative sometime soon.

ianat182
 
Avocet's stern tube is, as far as I can tell, original. If so, it's over 30 years old. There is a remote greaser on BOTH ends of it. It's absolutely chock-full of grease (some of it must be very old, I guess) over it's whole length. I've never had the stuffing box apart or changed a bearing (at either end), but I did add a flexible coupling of my own design some years ago. I've never had any water drip from the stern gland and it never gets more than hand-hot. The engine is only 12bhp and the longest continuous use of engine that we've done has been 8 hours. The prop does "windmill" if left out of gear.

I wonder whether your new engine mounts have "settled" now, and they're no longer quite as well-aligned?
 
I don't think you have much of a prob going on
Recently fiited a new stuffing box , shaft and gland packing.

On first trials she got' hot' like yours
So I ran the packing nut up hand tight, then just a tad more by spanner.

Ran her on bollards for an hour or two at 1500rpm.
Then it was about another 4 hours running until the box felt cooler .

Then at cruising revs (3000) for a similar time before I was confident to adjust further.

Yep, some grease oozed out, water dripped in
The final adjustments (had to tweek once or twice) sorted that out
Now she runs cool and I dose the box with 'Ramanol' , same as' Keenol' afaik but I reckon any marine grease will do
 
Think of all the drive shafts that have been used on applications ashore, driving machinery, etc. None of these bearings have water cooling, just lots of grease or oil.
 
Thanks all for the ongoing replies....lots to think about and mull over. I really appreciate the input. I don't think the mounts have settled....They shouldn't do that but I will check. Kawasaki....interesting as I have only run my boat for a very short time. I will tie up and run for longer at the weekend and see what happens!
 
Arctic Fox said:
Hi,

I am looking for some advice and guidance around the age old 'hot stuffing box issue. I think I know the reason but the more input the better, I think!

The problem is......I have recently re engined with a small Diesel. The engine was installed and lined up by a qualified engineer. I however, packed the stuffing box and tightened the packing nut etc. I did this as per the accepted methodology. I ran trials on Saturday but ended up with the 'Hot box'. By hot I mean I can hold it more or less indefinately but it wouldn't take that much to make it uncomfortable to hold. A summary of the pertinent facts are...

The shaft turns freely and windmills when knocked out of gear
There appears to be no excess vibration
The stainless shaft does not feel hot where it exits the tube
I get no water drips - even when the packing nut is slackened right off
There is not much heat @1000 rpm when just in gear - I happily motored round the harbour at this speed for 20+ minutes with no heat noticable
Heat appears at higher revs (2700/3000 rpm)

Now an admission (which might provide an easy answer)....In my naivity I thought 'grease is good' so when everything was in place I gave the stern tube / stuffing box a right good greasing via the lubricator. I now realise that this is not the smartest thing I might have done so.....

Do you think this is the reason for the heat or is something more sinister going on?
Will it damage the shaft/box if I run like this?
How can I solve the problem if it is the grease?

Thanks in advance and all advice will be greatfully received

Cheers

AF
Click to expand...
Sounds just right to me!
Stu
PS
I used to work on old fashioned pumps which had stuffing boxes on and so am quite happy with my thoughts!
 
Neil_Y said:
The heat is because of the grease, but you probably don't need to worry as it seems many people love the idea of lots of grease in the gland and they get by.

What it does (to a greater extent) on larger vessels where the shaft surface speed may be higher is cause shaft scoring which then degrades the sealing surface. The aim is to keep the shaft cool and lubricaed and water is still the best thing for the job, even the most advanced packing such as Duramax Ultra X relies on a small ammount of water (not grease) to help lubricate and cool. Grease is a poor conductor of heat and a shaft that heats up and then cools down will never have a great seal as it will change its diameter in what is a fixed diameter packing.

I think I'm outnumbered here but I believe a well packed and adjusted water only system is the best way to keep a good sealing surface on the shaft, and a stable shaft temperature and hence less dripping.
Click to expand...
Sorry Neil but I disagree with your thoughts!
Stu
 
The heat needs to get out some how, or reach a stable situation of thermal gradient, for ship stuffing boxes thermal conductivity has been one of the goals.
Have a look at the comparisons between flax, ptfe and Duramax here.
http://www.europeanmarine.co.uk/Duramax Ultra-X Compression Packing.pdf

We have seen failed bearings from blocked water channels which resulted in too much heat, but it was on faster, bigger shafts.

Maybe the sort of heat generated in a small low power system is easily coped with?

Where are the stuffing box designers when you need them? they would have a definitive answer.
 
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