How hot is too hot for stuffing box

[Spyro]

Boat back in today. I replaced stuffing box packing over the winter. I had no trouble with the old packing but had the shaft out to replace cutless bearing and stuffing box gaitor so thought I had better replace packing as well. I had never felt the temp of the box before so have no idea what is too hot or what is normal. I took the boat for a motor today and after about 15 mins the box was quite warm, not so warm that I couldn't keep my had on it but noticibly warm. I slackened off the packing nut a little until there was a drip- about 1 every minute when the engine was not running. I pushed in some more grease and the drip stopped. The shaft turns freely by hand and does not appear to be binding.
I ran engine again in gear but it still got quite warm. Is this normal?

 

[vyv_cox]

Mine has never been the slightest bit warm. The packing is at least 11 years old, I grease every two hours when motoring and it doesn't drip any water. I suspect that your new packing will take a little time to bed in and settle down, so the warmth will gradually reduce. Is there a drip when it is running? This is probably more important than having it drip when stationary.

 

[eyehavit]

Agree with vyv_cox post. The thing is the shaft has been removed and re-inserted along with a new bearing so there may be a number of possibilities (alignment, bearing high spots, pinching) as to why the stuffing box housing feels hot to touch. It is probably just the new packing bedding in but imo it is advisable to allow the seal to drip sufficiently to keep the housing cool while the shaft is turning.

 

[cliffordpope]

In most things to do with bearings the difference between acceptably warm and too hot is whether you can comfortably bear your hand on it. Also whether it stabilises at just comfortably warm even after hours of running, or whether that is just a prelude to getting hotter.
I wouldn't rely on drips keeping it cool if it really is overheating for some reason.
I would guess the temperature as reported is fine. Lots of things, bearings, motors etc run quite surprisingly "warm" if you are not in the habit of feeling them.

 

[Danny]

Sounds too hot to me. As I understand it, in a traditional stuffing box, the grease is there to waterproof the packing and not to act as a lubricant. While the shaft is turning there should be the occasional drip of water - about 2 a minute, say. This water lubricates the bearing surfaces between the packing and the shaft. If this is doing its job there should be little friction to generate heat (and wear the shaft). What little heat is generated should be conducted away by the shaft.

A twist of the greaser at the end of the day should waterproof the bearing so that little if any water drips through while the shaft is stationary.

 

[Richard10002]

[ QUOTE ]
I took the boat for a motor today and after about 15 mins the box was quite warm, not so warm that I couldn't keep my had on it but noticibly warm. I slackened off the packing nut a little until there was a drip- about 1 every minute when the engine was not running.

[/ QUOTE ]

When I was looking at my stern gland in December, (or was it October?), the general consensus here was that it does get warm, but not too warm to hold your hand on it, (bit like a cup of tea?) .... which suggests that yours is OK.

The other concensus seemed to be a drip every 30 seconds or so when running.

Mine gets warm after running in gear at about 1500 revs tied to the pontoon. I seem to be able to get it to drip every 10 seconds or so, or every few minutes... cant adjust it to anything in between.

I'll be having another look at it in April.

Cheers

Richard

 

[Krusty]

If your re-fit of the bearing, shaft and gaiter was out of alignment, I would expect you to have evidence other than just the warmth of the stuffring box; (vibration, different noise, etc.)
The heat generated by friction should be conducted away down the shaft easily enough to leave the box no more than pleasantly warm. If it is too warm, there is too much friction (obvious, I know!).
But the excess friction may be caused by roughening of the shaft, rather than over-tight packing.
Which is why it is most important to remove old packing with great care, preferably with a tool of softer material than the shaft, copper or brass for instance, to avoid scratching it.
I was taught that a shaft, at least the parts of it in bearings, should be treated with even more care than the bore of a rifle!

 

[Conachair]

asap sell a special tool for packing removal. http://www.asap-supplies.com/
They also do ptfe packing, got some but haven´t fitted it yet - anyone got any experience of the benifits of ptfe over graphite?

 

[Spyro]

Thanks for all answers. I'll take it for a longer run at the weekend and keep an eye on it (or hand) lets hope it just needs time to bed in. Adjustment is a bit of a bugger as acces is very restricted and needs removal of the battery every time I want to adjust it.

 

[Danny]

[ QUOTE ]
anyone got any experience of the benifits of ptfe over graphite?

[/ QUOTE ]Some years ago I used some PTFE packing I got from West Marine. This worked fine and seemed to be able to give a watertight seal without getting hot! The stuff looked a bit like green candle wax and you had to massage it into shape to fit it into the gland. There was some special lubricant that you used with it as well when you put the seal back together.

 

[TheBoatman]

Don't worry about it hand hot is OK. It's new packing and will bed in after a few hours use. The way you described it you can turn the shaft freely so it can't be binding.

As an engineer it never ceases to amaze me how some people expect their power trains to conform to such exacting standards when just about every boat has it's engine mounted on rubber, the in-board bearing is normally "floating" and the shaft is probably rotating at about 1000 - 1500 rpm when at cruising speed.
Of course it's going to get warm -why - because you have got to have friction generated when you turn a shaft at 1200 rpm that has packing as a bearing surface?

The only way you could ever guarantee that everything is "in-line" would be to fit the engine on to solid mounts - fit a c/v joint between the g/box and shaft, fit pukka bearings so that nothing can move out of line and then balance the shaft/prop & the coupling castings.

BUT that's expensive and very difficult to do in a small boat so the boat manufacturers have elected to go for the "lets float everything" line.

S h 1 t happens - so does friction!

Peter

 

[Gunfleet]

An aside, you say it's impossible to rigid mount everything in a small boat - do they do it in ships?

 

[Spyro]

Sounds good to me.

 

[pampas]

Yes