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How to adjust/repair RB250 horizontal movement bearing?

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How to adjust/repair RB250 horizontal movement bearing?

Postby mcduck » 03 Jan 2009 13:19

Hello,

I've got an RB250 arm which doesn't move smoothly on horizontal axis. The owner said he opened the 8 mm hex nut under the pivot and when putting back the started to move in "steps".

I think the horizontal axis bearing is either damaged or needs adjustment. I already read the thread about dismantling this arm, but there wasn't much info about actually repairing/replacing the bearing. So before i ruin it completely, i would like to have some info about repairing it. And please tell me where to get a completely new bearing, if it needs one.
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Postby zharca » 06 Jan 2009 11:28

Hi, the nut at the base of the spindle is carefully adjusted at the factory to set up the bearings and it's locked in place with glue. This is fairly soft when the arm is new, but sets rock-hard with time.

I have several suggestions:
1 - TAKE APART.
This risks ruining it, but in this case could be worth a try.
- Prise the plastic covers off the screws that hold the antiskate cover in place (these look like part of the moulding) and unscrew them.
- Loosen (but don't undo) the locking nut a couple of turns. If you are unlucky, the nut will stay in place and the arm yoke will unscrew instead, which is a major problem. You may now be able to press out the shaft, bearing on the nut, not the shaft. The brass shaft is very easily bent and the thread damaged. If someone has already had a go at it, it might already be ruined. The shaft may be very tight. The antiskate magnet should be removable but is sometimes stuck solid, in which case you must be very careful not to break the plastic cover.
- You can now drift the bearings out of the base, clean everything up and replace them. RS (http://www.rswww.co.uk) have the right ones. I have them if you have trouble getting some.
- Setting up the bearings needs care and practice. They should be very lightly lubricated, but not really "oiled". It's best to take the shields out, oil blow them out and drain them on kitchen towel for a couple of hours. Lock the bearing nut with "locktite"

2- Send it to John at Audio Origami.
Best option really, he's done dozens of these and is is one of the very few people who can put one of these back together again properly.

3 - I have a "service kit"
These are Genuine 2009 spec Rega RB251 bases complete with antiskate and arm yoke, ready to drop the arm tube straight on. It includes new armtube bearings, bearing stubs and caps. This is NOT a Rega-supported option!

4- Easiest option:
I do an exchange of broken arms for a new RB251! You could do this if the take-apart goes wrong.

Good luck!
Jeff
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Postby audioorigami » 12 Jan 2009 14:21

excellent advce there jeff

it could be the brass shaft is already bent with the1st owner ...as it is very soft metal
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Postby zharca » 12 Jan 2009 15:31

Yeah - absolutely right there Johnnie.
I've heard acetone (nail varnish remover) helps to soften the glue?

Jeff


........... who once gave up and took a hacksaw to one. :D
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Postby mcduck » 12 Jan 2009 22:36

zharca wrote:Yeah - absolutely right there Johnnie.
I've heard acetone (nail varnish remover) helps to soften the glue?

Jeff


........... who once gave up and took a hacksaw to one. :D


Sounds like a plan! I'll try it next...or not :D.

Zharca, did you get my pm?
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Postby zharca » 13 Jan 2009 12:14

Hi, sorry the header has been saying "you have no new messages" so something wrong there.

Sorted now and two points from the PM to add to here:

The RS part number is 540-306
the spec is 6x13x5 flanged, shielded.

Yes, the shaft can be very stiff. If you are inlucky enough to get one that doesn't want to move you really need a puller that can lock onto the thread or nut on the outside and press squarely on the shaft nut. Don't lever the arm yoke, that will almost certainly bend the shaft.
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