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  1. #1
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    Bottom bracket size issue

    Hi lads,

    First of all I'd like to say hi to everyone on this great forum. I am a new member here. I am not a professional cyclist nor experienced in bikes repair. I have a cheap Cross Hybrid bicycle (Cross Hybrid 700C) that I use for commuting to a place of work.

    Lately, I noticed loose in the bottom bracket axle, so I decided to replace the whole bottom bracket for a sealed Shimano cartridge. The measurment of the spindle width I have is 112mm long. As I am not experienced, I thought Shimano BB 113mm (BB-UN55) will fit it. So I ordered it. The package arrived today. After I opened the box, I realized the size of the spindle is shorter then 113mm. By using calliper I measured recieved spindle. It is 111mm long. I am wondering now, If I can still put it to the shell (68mm)? I had a feeling that the spindle is too short and arms may rubber the frame.

    I also think about purchase another (longer) cartridge that would be close to 112mm. Which spindle width, from the Shimano BB sizes (113, 115, 117, 122) matches my 112mm?

  2. #2
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    What you've got there is a square taper BB. The nature of the press fit that square tapers rely on means that no two installations will never be exactly the same. Don't think of it as exact measurements, think of it as size definitions.
    If the previous installation was otherwise OK (no rubbing, enough clearance etc) and that you have the correct part by spec( shell width, axle size etc), I'd just go ahead and mount it up. Adjust front derailer. Ride.

    OTOH it's entirely possible that the 115 mm version would work just as well.

  3. #3
    Andrew R Stewart Andrew R Stewart's Avatar
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    Before you take apart the old make note of a few dimensions for reference in deciding which replacement fits best. Chain line, inner chain ring clearance WRT the RH chain stay. Whether the old BB spindle is a symmetrical or an off set type (are both ends the same length or does the Rh side extend out further then the LH side). And of course the BB shell threading/width.

    Then you can Begin to make some assumptions about a replacement. But remember that even pros find themselves going to a second and different sized replacement at times. This is where your relationship with the place you purchase the BB from can change your experience. A good relationship with the LS you deal with will make the possible return and purchase of the second BB go smoother. A poor or lack of relationship (say as an on line purchase) might make the return of the not quite right first BB not so pleasant. Andy.

  4. #4
    Senior Member Bill Kapaun's Avatar
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    Your spindle is likely NOT symmetrical.
    It's VERY common that the DS end is a few mm longer than the NDS end.
    Look for a size code on the spindle such as 3-P, 3-S etc.
    There are charts to look up the symmetrical "equivalent" cartridge.

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