Stern gland - bearing?

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rajjes

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Hi,

I have a traditional stuffing box with the screw down greaser connected to the shaft tube with a short peice of hose.

I am replacing the packing however I'm not sure if there is some sort of replacable bearing/sleeve inside the stuffing box body?

Is it usual to have an inboard bearing or is the 'bearing' actually the packing?
 
There is unlikely to be a bearing inside the stern gland. The cutlass bearing provides support for the prop shaft. This is either on a 'P' bracket or mounted in the dead wood. The other end of the shaft is usually supported on a flexible coupling. There is a good description of re-packing in 'Simple boat maintenance' by Pat Manly although the photos are not up to much.
 
Just a couple of comments from personal experience:

A long thin wood screw is a good substitute for a dedicted packing extractor

Don't always expect to get the same number of new rings back as you took out. When I replaced my packing last time, I took out 5 rings but there was no way on earth I could get 5 rings back in & then tighten up the lock nut and I really did spend a lot of time struggling to do so. My set up same as the "old stuffing box" diag in MoodySabres link:). In the end I left it at four and it has proved OK in the 2 seasons since.
 
Karouise said:
Just in process of replacing cutlass bearing on my shaft.
The 'rings' for the stern gland - what are they made of? Presumably swindelries have them?
Click to expand...

Before you go dashing to the swindelries make sure you measure the size of your old stuffing material as they come in differant sizes!

For example as below on a 1" dia shaft the stuffing in my box is 1/4" sq.
Also when you have done the job do not throw away any material that might make another complete ring in the future, as others have said you will not be able to put back on all the rings you take out, some people add the last one if they get a drip in the future.

I get as many stuffing rings in as I can,then re-assemble the whole thing and tighten up, then take it apart again, and bingo you get another ring in!

One last thing, the stern tube rubber is not ordinary hose type rubber, it is specialy for the job thicker, on mine you will see it has a 3/8" wall thickness, got mine from http://www.tnorrismarine.co.uk/index.php

Mike

DSCN1629.jpg
 
Thanks for your feedback. I'm still a bit confused though as after some googling I found article on stern tube bearings and even half cutlass bearings!

I'm sure I do not have a bearing in the stern tube at the inboard end but still not sure if there is one in the stuffing box? Would the packing be really sufficient as a bearing?
 
The number of bearings you have or are needed are a factor of shaft diameter, hp and speed. Do you have a problem with rapid bearing wear noise and vibration? if not you probably have enough and they are probably in alignment.

Half bearings are sometimes used (in the stern tube) in addition to P bracket bearings and intermediate support bracket bearings. Normally a shaft bearing that is water lubricated is 4 x the shaft diameter in length.

If you have a water lubricated shaft bearing in the stern tube and you also have a greaser, excessive grease can cause these to wear prematurely as the grease can block the water channels which causes them to over heat. Grease is a poor conductor of heat.
For stern glands (with traditional packing) water is a good lubricant and coolant so the drip when running ensures a long life for shaft and packing.
 
I've been using bronze oilite bearings for stern bearings for the past couple of decades. They are super cheap and take a bit more heat. I fill my stern tube with grease from a permanently mounted grease gun, so I think about heat, altho friends with rubber bearings have had no problem with grease filled stern tubes in the last couple of decades.
I drilled and tapped my stern tube with a 1/8th pipe thread the standard thread on a grease gun hose, eliminating the need for a nipple.
If you cut a couple of grooves in your stern tube , either side of the shaft, about 1/4 inch wide by about 3/4 inch long, that will let you use a centre punch to tap out your old bearing , eliminating the need to remove the shaft .
 
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Modern bearings bedded on epoxy only require some heat and they slide out by hand as they are a clearance fit, no need to punch or tap, or remove shaft.
 
MoodySabre said:
No internal bearing - the purpose of the stern gland is to keep the water out, not to support the shaft. Good description on diagrams here.
Click to expand...

Wrong, some sterntubes do have internal bearings, mine are white metal, with external cutlass and cutlass in the A brackets. My shafts are bronze. Others have cutlass type, some have nowt, some have bronze.
 
Neil_Y said:
The number of bearings you have or are needed are a factor of shaft diameter, hp and speed. Do you have a problem with rapid bearing wear noise and vibration? if not you probably have enough and they are probably in alignment.

Half bearings are sometimes used (in the stern tube) in addition to P bracket bearings and intermediate support bracket bearings. Normally a shaft bearing that is water lubricated is 4 x the shaft diameter in length.

If you have a water lubricated shaft bearing in the stern tube and you also have a greaser, excessive grease can cause these to wear prematurely as the grease can block the water channels which causes them to over heat. Grease is a poor conductor of heat.
For stern glands (with traditional packing) water is a good lubricant and coolant so the drip when running ensures a long life for shaft and packing.
Click to expand...

Neil is spot on....i got carried away with too much grease and had to replace the lot!
 
rajjes said:
Hi,

I have a traditional stuffing box with the screw down greaser connected to the shaft tube with a short peice of hose.

I am replacing the packing however I'm not sure if there is some sort of replacable bearing/sleeve inside the stuffing box body?

Is it usual to have an inboard bearing or is the 'bearing' actually the packing?
Click to expand...

Hi,I had a share in a Hunter 27 OOD some years ago.The stern gland/stuffing box was as you describe.When the greaser was screwed down it just pushed the expensive grease into the sea.I found that some stuffing boxes have a smaller diameter section just behind the grease outlet so as to give a resovoir and to let you know when to stop turning the greaser-you can feel some back pressure.My solution was to fit two conventional oil seals after having the housing licked out a couple of thou. on a lathe.once this was done Honda 125 motorcycle wheel bearing seals fitted the housing and the shaft nicely.Also got £25.00 from PBO as a technical tip.Result.
 
bearing noise and leaking stern gland

Neil_Y said:
The number of bearings you have or are needed are a factor of shaft diameter, hp and speed. Do you have a problem wif not you probably have enough and they are probably in alignment.

Half bearings are sometimes used (in the stern tube) in addition to P bracket bearings and intermediate support bracket bearings. Normally a shaft bearing that is water lubricated is 4 x the shaft diameter in length.

If you have a water lubricated shaft bearing in the stern tube and you also have a greaser, excessive grease can cause these to wear prematurely as the grease can block the water channels which causes them to over heat. Grease is a poor conductor of heat.
For stern glands (with traditional packing) water is a good lubricant and coolant so the drip when running ensures a long life for shaft and packing.
Click to expand...

Bunyipbob
I recently purchased my first yacht and find that the stern gland has a rol rol noise on motoring and quite a leak from the stern gland when moored. It takes a lot of grease to stop it each time i use the motor.Do i just need to repack the stuffing box? and do i need to replace a bearing and where is it located.The yacht is 20 years old. Grease squeeses out from the gland readily. (Question)
 
bunyipbob said:
Bunyipbob
I recently purchased my first yacht and find that the stern gland has a rol rol noise on motoring and quite a leak from the stern gland when moored. It takes a lot of grease to stop it each time i use the motor.Do i just need to repack the stuffing box? and do i need to replace a bearing and where is it located.The yacht is 20 years old. Grease squeeses out from the gland readily. (Question)
Click to expand...

If it is a "conventional" stuffing box then sounds like it needs repacking. The grease is not here to keep the water out, the packing does that. The noise could also be the outer bearing of the stern tube. Normally this is a cutless bearing in a housing. It is water lubricated and does eventually wear.
 
Tranona said:
If it is a "conventional" stuffing box then sounds like it needs repacking. The grease is not here to keep the water out, the packing does that. The noise could also be the outer bearing of the stern tube. Normally this is a cutless bearing in a housing. It is water lubricated and does eventually wear.
Click to expand...

I'd agree, it probably needs re-packing but the first step would be to tighten the gland as it stands. It needs checking and adjusting at least annually. Check during the season for drips and if it starts getting excessive, re-tighten.
 
As Tranoma and ala said.

First adjust gland (squezes packing should drip when turning and not drip when stationary, gland should not get hot)

Second repack with new stuffing, adjust run and adjust again.

But if you are out of the water inspect the stern tube to see
1.Do you have a bearing in stern tube
2.Is the tube free of debris and grease to allow water to flow freely to gland and through any bearing that's there.
3.If there is a bearing is it worn, this will not help a gland as the shaft will be flexing more.

Conventional glands can work very well with just water as it works as a coolant and lubricant for bearings (if there are any) and stuffing
 
WHAT's THE GREASE FOR?

Tranona said:
If it is a "conventional" stuffing box then sounds like it needs repacking. The grease is not here to keep the water out, the packing does that. The noise could also be the outer bearing of the stern tube. Normally this is a cutless bearing in a housing. It is water lubricated and does eventually wear.
Click to expand...
I've never been quite clear what the greaser is for. I've assumed that it is to completely stop dripping when the engine is not running but, when I think about it, the grease is introduced aft of the packing and will therefore fill the stern tube and the cutlass (cutless?) bearing eventually. However, on my boat, it could be observed extruding from the gland. So, what prevents it from going into the stern tube where it is going to impede/block the flow of water to lubricate/cool the gland?
 
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