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Thread: Old Stumpy BB

  1. #1
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    Old Stumpy BB

    So I'm trying to revive a '95 Stumpy M2 and need to replace the bottom bracket. I'm waiting on the tool to extract it (square taper) but want to order a replacement while I wait. Old bikepedia info says I have a Shimano UN-52 BB, 110mm spindle (for the '96 at least... no info on the '95). How exactly do I translate that to a modern BB? I can't find much with those numbers.

    Thanks much.

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    I'm assuming you are using the same crank, go to Amazon and search for shimano un55 and select 68x110, costs $20. I bought one to replace an IRD BB and so far it has lasted almost 2 years (3000+ miles). You want the un55 because it has metal cups, lesser models have plastic cups and often times aren't any cheaper. Make sure you torque them down properly or they will come loose on you.

    Different crank may likely require a different BB.

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    Thanks, man -- ordered.

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    On that note -- is there a way to adapt a 30mm BB (like a BB30) to a frame like this designed to take the old threaded BBs?

  5. #5
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    Quote Originally Posted by zayd View Post
    On that note -- is there a way to adapt a 30mm BB (like a BB30) to a frame like this designed to take the old threaded BBs?
    Yes and no. You need the special BB and also a modified spindle for the crankset. More info here:

    What is needed to make a BB30 fit on a 68mm BB?


    Also, I think HoldTheOnions gave you some wrong advice. Your existing BB shell is likely a 73mm, not a 68mm. Bikepedia shows the '96 is a 73mm so yours may be the same.

    You should measure the width of the BB shell (the frame) and determine if it's 68mm or 73mm. Your old bottom bracket would also list the shell width measurement. Using the wrong width will cause chainline problems and push your crankset too far away from your bike.

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    jtmartino -- thanks. I should be clear that I had the same conclusion for the same reason, so I ordered both a 68mm and a 73mm BB.

    It looks like that mod is too pricey for an old Stumpjumper, so I'll stick with my old LX cranks or find something a little better. I just want this bike to hold me over long enough to fund a FS Stumpjumper build.

  7. #7
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    Quote Originally Posted by zayd View Post
    jtmartino -- thanks. I should be clear that I had the same conclusion for the same reason, so I ordered both a 68mm and a 73mm BB.

    It looks like that mod is too pricey for an old Stumpjumper, so I'll stick with my old LX cranks or find something a little better. I just want this bike to hold me over long enough to fund a FS Stumpjumper build.
    Good call on ordering both! Using the wrong size causes a lot of headaches for people with chainline.

    I think the only reason to use BB30 would be for increased stiffness (and maybe some weight savings.) Unfortunately even if there was a non-pricey way to slap BB30 on your existing frame, the setup would not be as stiff as a BB30 specific frame. An outboard bearing crankset would really improve your current situation. There's some good stuff on sale at PricePoint and Jenson USA - I've had good luck with RaceFace and Shimano stuff, although the Shimano BBs tend to be a little better long-term.

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