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Thread: R20 bb

  1. #1
    Senior Member Elad63's Avatar
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    R20 bb

    I am planning on changing my bb. I searched and know about the UN72 . I called my LBS and they said that a UN54 will work, and that they can get one UN54 for $20. During my searches I ran across someone suggesting to us the UN54. Has one one tried this one and how is it holding up. I would like to put a double on the front.

    Also, is it possible to keep the orginal cottered spindle and just add a cottered double chainring. I now have a 9 speed squeezed ( took two of us ) on the rear. The first cog just barely scraps the chainstay, so I will have to take it back off and put a spacer on.

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    A Raleigh Twenty bottom bracket is Raleigh's 26 TPI size. You can go with a Shimano UN73 bottom bracket. And have the threads stripped to BSC 24 TPI. A Phil Wood 26 TPI bottom bracket is the most expensive solution.

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    Senior Member wahoonc's Avatar
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    Remember that the R20 uses a wider than normal BB. Many people have them faced down to reduce the width to better accommodate a modern BB.

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    my method for altering a frames width is to measure the width.
    say its 110mm
    and it needs to be 135mm. a difference of 25mm.

    then put the bottom bracket shell in a vice.
    then get a scaffold pole. put it on the inside of the right drop out, and the other end on the right side of the seat tube. then lever away from the centre line. till the measurements 110 + 12.5= 122.5mm
    then put the pole into the left side and open it to 135mm.

    If you dont have the frame set to the width of the hub, it will stress the axle and bearings. Also it'll mean that the wheel will be a pain to remove. And you know it'll flat on a cold dark wet night.

    Might be a good idea to move the axle through the cones a bit. as the Raleighs drop outs arent the thickest metal. move the axle to the drives side a couple of mm. be easier to fit the spacer you mentioned.

    Ive got a Hercules shopper bike. Its got a loop tail rear frame. had an idea to fit a 9 speed disc hub to the rear. Ive widenened the rear end. Its a Raleigh brand frame, but has a normal BB thread. might have to mod the drive side frame more to get the chain on. An 11 to 32 cassette and 52 chain ring, would give 32" to 95" gears. might get by with a short cage mech too. So would have reasonable ground clearance.

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    Alec is right about cold-setting the frame- I did mine from the 116 to 135 to accommodate an IGH I found cheap. It wasn't difficult and won't damage the frame if done carefully.

    Also, the UN54 won't work without some modifications to the BB shell- it needs to be faced 3 mm from 76 mm width to 73 mm width- and either needs to be re-tapped to 24 TPI from 26 TPI, or the bottom bracket modified. I chose to modify the bottom bracket- three rows of 24 TPI threads will screw into a 26 TPI shell- so I ground off all but the outer 3 rows of threads on the bottom bracket and installed it normally. It has been working perfectly for the last year or so, no loosening or creaking.

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    Alec knows his poop Cold set is the hot way to go

    The UN72 works really slick but you have to be concerned with the fact that they are hard to come buy and if the one you were lucky to find ever does go bad, you'll have to find another one... I think I have two extras for that reason...

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    you can get bottom bracket cartridges that have no external threads.
    they have a smooth cup that screws onto the cartridge.
    works a bit like an allen key road bike brake spindle.
    so you dont have to retap or fit expensive cups to it.
    heres a YST one on USA ebay.
    http://cgi.ebay.co.uk/New-YST-Thread...item53da48eb5a

    theres other lengths of spindle from YST

    other brands do a 73mm bottom bracket width.

    think they are all square taper. So you cant use them with the latest Isis cranks.
    Last edited by griftereck; 10-28-09 at 05:59 AM. Reason: missed a word

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    I know one option I had looked at here in the states was a special BB cartridge that was used for bikes that had cross threaded BBs... I never got around to ordering it but it was pretty cheap. Its probably about the same thing that Alec(Griftereck) is talking about.

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  9. #9
    my nice bike is at home kraftwerk's Avatar
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    I think I used Phil Woods cups with the Shimano UN72 ( UN 73?) spindle and bearings but my memory for these things is not primo...
    I was tempted to grind the shell down a bit but never did, as it all worked out.

  10. #10
    Senior Member stevegor's Avatar
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    Quote Originally Posted by kraftwerk View Post
    I think I used Phil Woods cups with the Shimano UN72 ( UN 73?) spindle and bearings but my memory for these things is not primo...
    I was tempted to grind the shell down a bit but never did, as it all worked out.
    According to the legendary Sheldon Brown, the 73mm UN72 is the BB that is used for the R20.
    Best length for the spindle is approx 113mm. Remembering that the R20's BB shell is 76mm wide which means when you wind in the Phil cups they will be recessed by 1.5mm each side.
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