New Rudder bearing is too tight. Now what?

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NPMR

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In the winter refit, I had a new lower rudder bearing made up, which I fitted not long before relaunch. The rudder was stiff when moved without the tiller and I asked the yard if they felt it was OK (they made the bearing).

Net result launched anyway, and I now find that the rudder is flaming stiff. Haven't tried the autohelm yet but it feels as though it might struggle to move the tiller

As the bearing is a tufnol-type material (oil impregnated something-or-other) shall I just live with it as it has to free up in the end (simple wear and tear will do that, which is why I had to have a new one in the first place), or is it something I really need to sort (lift out/remove bearing/rebore/refit etc).

Undecided.
 
Surprisingly, if many plastics are allowed to rub heavily on stainless steel, it is the steel that wears. It shouldn't happen with a plastic intended for the job but many are glass filled to provide the base polymer with mechanical strength. Even with the best ones the steel wear debris becomes embedded in the plastic and becomes abrasive.

I would ream the bearing out for a good fit. Seems to me the yard should pay if they made it and presumably measured everything?
 
NPMR said:
In the winter refit, I had a new lower rudder bearing made up, which I fitted not long before relaunch. The rudder was stiff when moved without the tiller and I asked the yard if they felt it was OK (they made the bearing).

Net result launched anyway, and I now find that the rudder is flaming stiff. Haven't tried the autohelm yet but it feels as though it might struggle to move the tiller

As the bearing is a tufnol-type material (oil impregnated something-or-other) shall I just live with it as it has to free up in the end (simple wear and tear will do that, which is why I had to have a new one in the first place), or is it something I really need to sort (lift out/remove bearing/rebore/refit etc).

Undecided.
Click to expand...


oil impregnated
Oilite perhaps
http://www.oilite.com/bearings.asp?type=plus
 
OK, so now the lift-out is booked, I have the problem of how to 'open-out' the bearing, on the quayside.

I had a discussion with the man who made the bearing and his advice was that I needed a 'knife' or cutting tool, not an abrasion one.

But, I've just tried a Dremel with a small emery/sand wheel, on the old bearing and it abrades very easily. Lots of dust etc so I'm sure it will do some kind of a job. The trick will be to keep it even so that there are no high spots.

Any suggestions? I'll have mains electricity and a workmate bench and a vice but basically working on a concrete jetty with limited means of ensuring the work is 'true'. Hand tools only apart from the Dremel.

What else should I think about?
 
I would use sandpaper wrapped around a dowel, the Dremel will be difficult to control and keeping the shape will be hard. Is there any possibility the bearing(s) isn't (aren't) aligned properly?
 
savageseadog said:
Is there any possibility the bearing(s) isn't (aren't) aligned properly?
Click to expand...

I am worried this might be the case, as the man who made the bearing said it was 'free' when he tried it on the shaft but it is now very much too stiff (I can hardly move the tiller!)

So something has changed since it was made but before it was launched. So, out of alignment is a possibility.

As the shoe on the end of the skeg is almost impossible to fit incorrectly, I could only hazard a guess that, if this is the case, the bearing is sitting in the shoe in some way that is wrong.

Still leaves me with the problem of aligning it all properly, mostly just by eye?
 
Your man is correct. Using abrasive methods is likely to leave particles in the plastic, which will cause damage later on. A big round file would be OK as it works by cutting. Quite difficult to ensure accuracy though. Ideally you need an adjutable reamer of the appropriate size, try Googling it. You might even be able to hire one.
 
NPMR said:
... the man who made the bearing said it was 'free' when he tried it on the shaft but it is now very much too stiff (I can hardly move the tiller!)

So something has changed since it was made but before it was launched. So, out of alignment is a possibility.
Click to expand...

So also is the possibility that it was made from a type of plastic that absorbs water and swells. There are several different grades of Tufnol, and some of them absorb water. Nylon does as well, and will swell by a considerable amount, certainly enough to cause binding. If your engineer has used acetal or Vesconite then it will be an alignment problem, not water absorption.

The correct tool to open the bush out is an adjustable reamer, but buying one especially for this is really not practical. You could possibly make a scraper tool by cutting 2 flutes along a piece of bar with an angle grinder. Failing that take the bush out and rebore it (or throw it away and make another from the correct material).
 
You could make a DIY tool from two or three electric planer blades set into a rod or dowel.

Regarding alignment, it might be that the lifting and shoring operations have moved the hull a little.
 
Just measured the hole in the old, worn bearing and it's 29mm dia. (1" and 1/8") So quite big.

Local hire shops are a no/no on that size and Axminster's biggest is too small even if I were to buy one.

Looks like the "dowel and abrasive" (despite the drawbacks) is looking like the best option, other than having a workshop on standby to cut a new bearing on a lathe, all against the clock as the tide ebbs back out! (or a file)
 
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Nigel

If your Sabre is anything like mine...just leave it. I did mine myself this winter (new bearing was turned professionally though). The new bearing was a perfect fit on the shaft, however there seems to be an alignment problem between the rudder top tube and the heel fitting, as evidenced by the wear pattern on the old bearing.

When I put mine back together, I put the shoe on the rudder, and then had to shove the whole rudder forwards by about 10mm to get the shoe back on the skeg. This fore and aft misalignment is what caused the friction on my boat.

I used acetal, which is apparently the best stuff to use...you might want to make 100% sure that the yard used the right grade of tufnol and there's no swelling. Also make sure that the collar under your tiller is done up tightly so the rudder is hanging from it, rather than the blade sitting on the bearing at all.

Mine did seem tight but has loosened up a bit already, could just be the lubrication of the water (although some Portsmouth harbour mud grinding paste and a good sail seems to have helped!) and it feels perfect now. No "sticktion" but I can leave the helm if needs for short periods.

I have some acetal if you need a bit but I would have a word with the machinists and they guys who fitted it before you make any decisions and see if what I've written above rings any bells. I was surprised just how little difference there was on the micrometer between "totally knackered" and "brand new". Adjusting with sandpaper and dowels will be very tricky, and if your shaft is out like mine, you need to make a slightly oval hole, which will be flipping impossible.

EDIT...However my one big concern is that on the S27OA website over the winter you said that your bill for yiur bearing said "nylon"...and this might swell which might be your problem. If so, it's up to the yard to sort it!

Good luck.
 
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All plastics absorb water and swell, just some less than others; I'm guessing that the fitter who made the bearing tested it on the rudder post before it was fitted to the hull. When it was pushed into the hole, the hole in the middle gets smaller as the bearing is squeezed by the hole and the plastic, being squidgy, deforms. That's probably why your rudder was stiff even sat on dry land; once the plastic absorbed a bit of water the stiffness gets worse. My old man had his rudder bearing out to be reamed larger 3 times before he got it right, and that was turned from an oil-loaded nylon. Get the yard to do it properly and take the bearing out.
 
All bearing materials should be finished to manufacturers spec's, the new clearance should include (if press fit) clearances for bore closure, moisture absorption and unscheduled thermal expansion as well as the standard minimum running clearance. It's not as simple as if it works on the bench it'll be fine in use.

To have a bearing working well and getting a long life this clearance needs to be done accurately, a bearing that is too big will wear much more rapidly and a tight one will either seize up as it is worked (gets warm) or start to fall apart.

As an example we publish the clearance figures for Maritex.
http://www.h4marine.com/Downloads/Maritex AQUARIUS General Calculator REV 20100519.xls
Under the table the clearance figure is broken down into its parts, finish is to within 0.1mm on smaller bearings.

As Iain said if it was Nylon this has a much higher moisture absorption than Delrin/Polyacetal and even more than the latest composites. But the interesting factor to look at is the thermal expansion rates, this is often far greater than any moisture related changes.
 
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Lakesailor said:
Surely a machine shop could mount your bearing and cut the inside surface to the correct diameter?
Click to expand...

They probably did not use the correct calculation for swelling especially if the bearing compresses when fitted to the heel. It is normal practice to machine tufnol oversize dry so that the clearance is correct once in use. The consequences will be dire as any ships engineer of uncertain age will know when the cutlass bearing is incorrectly machined. :D:D:D:D
 
If you are still looking to ream out the bearing why not use an engine cylinder reamer? They are usually 3 or 4 stones spinning inside the bore on a drill press using the centrifugal force of the stones as the only cuting force.
 
I think you should get the contractors who you paid to make a replacement bearing down to your vessel and ask them to sort it out. If the bearing was made for your stock and the bearing is stiff, then the bearing has not been made to the correct size. Simply hand grinding out the inner surface of a bearing is not the correct way forward. The bearing needs to be removed and re-machined.
 
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