Stern tube getting really hot

[Bee]

If you take the nuts off the long studs off the front, should be 4 of them or just 2 nylock nuts the 'top hat' plate will ease along the shaft - where it will probably come up against the plummer block. You will need to undo the hold down bolts and also the one or two little grub screws that fix the 'collar' of the plummer block to the shaft,it will then slide up the shaft. It is not really a thrust bearing but they are often used as such., You can then put new packing in. If you try to pick the old stuff out the water will come in so I really don't advise doing that but it wouldn't hurt to shove a bit of grease in there. My guess is that the packing is hard and dry and tight.

[bizzard]

 

Good init.

If you take the nuts off the long studs off the front, should be 4 of them or just 2 nylock nuts the 'top hat' plate will ease along the shaft - where it will probably come up against the plummer block. You will need to undo the hold down bolts and also the one or two little grub screws that fix the 'collar' of the plummer block to the shaft,it will then slide up the shaft. It is not really a thrust bearing but they are often used as such., You can then put new packing in. If you try to pick the old stuff out the water will come in so I really don't advise doing that but it wouldn't hurt to shove a bit of grease in there. My guess is that the packing is hard and dry and tight.

A really really stout thrust block are the Dodge Fenner with twin mounting bolts either side and twin face to face Timken tapered roller bearings.

[Ray T]

Good init.

A really really stout thrust block are the Dodge Fenner with twin mounting bolts either side and twin face to face Timken tapered roller bearings.

 

 

Mmmmm beefy.......................

Edited February 28, 2015 by Ray T

[bottle]

You are not going to like this but the best plan would be out of water and remove shaft, clean it all up, check for wear, new packing and grease.

[Ray T]

?

.

Edited February 28, 2015 by Ray T

[bizzard]

 

That's the type Ray. Others make similar. GKN, BRT I can't remember at the mo.

[bizzard]

It might be best to go down the weed box and grab hold of the propeller and powerfully yank it up and down to try and judge the shaft and or tubes wear.

[Mitchellmoxo]

Hi buzzard definitely no movement as I was playing with the prop when it was out the water I don't think its an alignment issue from reading I think it's combination of the packing gone and lack of grease taking path of least resistance and maybe not getting into all the areas needed?

[Keeping Up]

 

This is a "Plummer" block. We have one on our boat. It is designed to transfer some of the thrust to the boat hull thereby relieving the pressure on the engine mountings. It looks well greased to me.

This is "ours"

 

 

In the original picture the copper tube feeding the gland looks fairly new? Is it blocked at all? Is the grease actually getting through

 

I stand ready to be corrected but I don't think a Plummer Block is actually meant to transmit any thrust, is it? Our Plummer block (which looks very similar to this) definitely doesn't transmit any thrust because the grub screws of the centre collar are left loose and the shaft can slide forwards and backwards in the centre of the bearing, thus allowing the engine some extra degree of movement on its flexible mounts if needed (which it does, sometimes, if something big gets caught on the prop). Here's a picture of ours, from when the engine was being changed last year; certainly the clearance between the stern tube and the plummer block is much much greater than that in the OP's picture, and I agree with Alan that any slight misalignment on the OP's could cause significant stress on bearings and possibly cause them to heat up.

 

Sam_1738a by Keeping Up, on Flickr

 

One other possibility might be wear on the shaft. On ours the shaft had worn significantly (to half its original thickness) in a nice taper, and the packing would sometimes be drawn into the taper and would partially seize.

 

Edited for spilling mistooks

Edited February 28, 2015 by Keeping Up

[Tom and Bex]

We had exactly the same when our boat was put back in the water after some time out on hard standing. Heated up so much the the shaft seized completely and looked just like yours in the photo.

 

Turns out the alignment of the new stern gear we had fitted while the boat was out of the water changed when it was put back in and needed extra thick packing put under the plumber block bearing to make it line up. Been fine ever since.

 

Tom

[Ray T]

I never knew this but apparently plummer blocks and pillow blocks are two different animals.

 

http://en.wikipedia.org/wiki/Pillow_block_bearing

 

"These differ from "plummer blocks" which are bearing housings supplied without any bearings and are usually meant for higher load ratings and corrosive industrial environments. However the terms pillow block and plummer block are used interchangeably in certain parts of the world."

Edited February 28, 2015 by Ray T

[RLWP]

Hi buzzard definitely no movement as I was playing with the prop when it was out the water I don't think its an alignment issue from reading I think it's combination of the packing gone and lack of grease taking path of least resistance and maybe not getting into all the areas needed?

Why was the boat out of the water?

 

Richard

[Mitchellmoxo]

Hi Richard sorry I didn't reply to the last message. Had the boat overplated.

 

The help you receive on this forum is great really appreciate it.

[RLWP]

And Was some of the welding done near the sterntube?

 

Richard

[RLWP]

My guess is that the Welding has distorted your hull and the packing underneath the Plummer block needs readjusting.

 

It isn't the packing in the stern gland, if it was it would be the very front of the sterntube getting hot. Yours is getting very hot indeed along the whole length of the bearing. As the Plummer block is close to the sterntube, any misalignment will put quite a load on the bearings

 

As a quick fix, take the two bolts out of the forward bearing and see what happens. If the bearing pops up, you need to put more packing underneath (strips of beer can). If you cannot pull out the packing easily the block is sitting too high. lever the block up and fiddle it out. Then see what you can slip back under the bearing.

 

Richard

Edited February 28, 2015 by RLWP

[Tom and Bex]

As Richard says above, this is exactly what happened to us. As a quick fix to get back we unbolted the plummer block and it jumped up about 10mm so we just ran the engine with it like that to get back. As in your photo, ours overheated the stern tube all the way to the back too.

 

Tom

[Tony Brooks]

I note quite a bit of fairly clean grease around the front of the gland. That and the OPs assertion that the gland does drip a bit makes me suspect a shaft alignment problem is more likely so I go with Richard and whoever mentioned engine mounts. If a mount or engine foot did fail the plumber block is likley to act as a pivot and if so the plumber block will be pushed hard onto the cross member.

[Mitchellmoxo]

My guess is that the Welding has distorted your hull and the packing underneath the Plummer block needs readjusting.

It isn't the packing in the stern gland, if it was it would be the very front of the sterntube getting hot. Yours is getting very hot indeed along the whole length of the bearing. As the Plummer block is close to the sterntube, any misalignment will put quite a load on the bearings

As a quick fix, take the two bolts out of the forward bearing and see what happens. If the bearing pops up, you need to put more packing underneath (strips of beer can). If you cannot pull out the packing easily the block is sitting too high. lever the block up and fiddle it out. Then see what you can slip back under the bearing.

Richard

Hi Richard,

 

Yes welding was done around that area as you can see here:

 

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This does make sense as yes it is the whole stern tube getting hot so I assume it's rubbing on the shaft? I will have to take the Plummer block bolts off and have a look. So i assume that there will already be some spacers under the bearing mount so it's a case of either taking them away or adding more in depending on alignment?

 

Many thanks I owe you and a few others a beer!... I will need the can back though incase it needs raising

Edited March 1, 2015 by Mitchellmoxo

[NB Lola]

Let us know how you get on

[Bee]

Many thanks to Ray T and Bizzard, It has long been a niggle of mine that many boats do not have a proper thrust bearing, Aquadrives and Python drives have a proper thrust bearing but hundreds of boats (including a couple that I built years ago) just use a plummer block with a couple of grub screws. I never had a problem but I was always aware that it was a bit iffy. If anyone here is building or fitting a new engine to a boat then that bearing in the picture is something to budget for.

[nicknorman]

Many thanks to Ray T and Bizzard, It has long been a niggle of mine that many boats do not have a proper thrust bearing, Aquadrives and Python drives have a proper thrust bearing but hundreds of boats (including a couple that I built years ago) just use a plummer block with a couple of grub screws. I never had a problem but I was always aware that it was a bit iffy. If anyone here is building or fitting a new engine to a boat then that bearing in the picture is something to budget for.

Why do narrowboats need a "proper thrust bearing"? Most gearboxes, such as the popular PRM150, state that they have built in thrust bearings that are quite capable of taking the full rated load which in any case, is very rarely if ever encountered on most narrowboats. So the inbuilt thrust bearing is operating way below its rated load for nearly all the time.

 

Of course, you need to ensure that the engine mounts are capable of transmitting that load to the hull.

 

Adding an external thrust bearing just seems to be adding a layer of complexity for no real benefit. Or am I missing something? I am by the way, only considering close coupled modern engines, not mid-engines with a long and possibly offset prop shaft.

[RLWP]

Hi Richard,

 

Yes welding was done around that area as you can see here:

 

 

Bingo! Nothing you had said before added up to an issue big enough to cause that problem. You hadn't repacked or tightened the gland, and it was OK before so why cause a problem now?

 

I was wondering if you had got something wedged up inside the tube from the propeller end

 

If you are fortunate, there will be packing under the block, and this needs readjusting - or maybe the block has moved sideways. It isn't easy to predict what the welding stresses have done to the hull

 

What is between the bearing block and the gearbox?

 

Richard

Edited March 1, 2015 by RLWP

[alan_fincher]

Many thanks to Ray T and Bizzard, It has long been a niggle of mine that many boats do not have a proper thrust bearing, Aquadrives and Python drives have a proper thrust bearing but hundreds of boats (including a couple that I built years ago) just use a plummer block with a couple of grub screws. I never had a problem but I was always aware that it was a bit iffy. If anyone here is building or fitting a new engine to a boat then that bearing in the picture is something to budget for.

 

These comments need to be treated with some caution, I feel.

 

Many marine gearboxes are actually designed on the assumption they will be taking the thrust of the propeller, and some older gearboxes actually must take the thrust of the propeller. If you look at the manuals for such gearboxes, if you wished to run with a thrust bearing in addition to the one in the gearbox, then the gearbox had to have it's bearings changed to a different type.

 

So, as in all things like this, it is not quite as obvious as it may initially seem, and each case may have different considerations.

[Mitchellmoxo]

 

Bingo! Nothing you had said before added up to an issue big enough to cause that problem. You hadn't repacked or tightened the gland, and it was OK before so why cause a problem now?

 

I was wondering if you had got something wedged up inside the tube from the propeller end

 

If you are fortunate, there will be packing under the block, and this needs readjusting - or maybe the block has moved sideways. It isn't easy to predict what the welding stresses have done to the hull

 

What is between the bearing block and the gearbox?

 

Richard

 

Hi Richard, yes makes complete sense regarding the welding - there is some kind of adapter block between the bearing and gearbox, shame Im not at the boat or I would of taken a photo.

 

Regards

[RLWP]

Something with a flexible element to it?

 

What I'm trying to work out is if you have to sort the alignment of just the bearing block, or are you going to have to do the engine as well

 

Richard