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  1. #1
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    Bottom Bracket thread

    Whats the thread difference between English threads and normal threads?

  2. #2
    Former Bike Wrench
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    English threads are the norm these days except on some Italian road bikes.

    English-1.37" x 24tpi...left hand threads on driveside...common BB width is 68mm or 73mm (wider for some DH frames)

    Italian- 36mm x 24tpi...right hand thread bith sides...70mm BB width

    Others such as French and Swiss are pretty much non-existent anymore.

  3. #3
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    so if it's 68mm or 73mm then it should be english even though not stated?

  4. #4
    Former Bike Wrench
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    unless your working on a 30 year old French bike (French was 68mm)...it'll be English.

  5. #5
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    Quote Originally Posted by mtnbiker72
    unless your working on a 30 year old French bike (French was 68mm)...it'll be English.
    thanx... you just cleared up a lot for me... thanx!!!

  6. #6
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    I just bought a deore shimano crank set for my trek 4300. The stock bottom bracket doesn't work because it is too long. And the front derailler isn't able to shift to the 3rd gear. How do I know which bb to buy? I bought three different ones, but then the length seem to only differ on the non-gear side, not the side with the gears. I hope this makes sense.

  7. #7
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    Square taper or Octalink?

    Quote Originally Posted by ltran
    I just bought a deore shimano crank set for my trek 4300. The stock bottom bracket doesn't work because it is too long. And the front derailler isn't able to shift to the 3rd gear. How do I know which bb to buy? I bought three different ones, but then the length seem to only differ on the non-gear side, not the side with the gears. I hope this makes sense.
    IIRC, most Shimano MTB square taper will work fine with a 110 or 113mm spindle (to produce a chainline somewhere between 47.5 and 50.0mm). Depending on the model year, an Octalink Deore crankset might require a 118 or something like a 125mm spindle (I think somewhere around 2004 Deore and LX went to funky BB spindle sizes). If the crank is a 06' or 07' model, you can go to pretty much any shop and ask them to look up the size in their QBP catalog. Or just call Shimano tech support and provide them with the model number (they've been reasonably helpful IME).

    BB spindle sizes are progressing somewhat towards more consistent sizes (only applies to older, non-outboard-bearing cranksets), but unlikely to ever reach any kind of "standard" since new crankset designs seem to be coming out almost yearly. Keep in mind that every bottom bracket has two measurements (besides thread pitch, virtually all MTB BBs are ISO/English 1.37x24TPI): the frame shell width (68 or 73mm, usually) and the spindle length. The shell width has to do with frame compatibility, the spindle length with the crankset. HTH.

    -R

  8. #8
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    In reply to Unemployed_mechanic response. Thanks, I will go back to the LBS and bring both the new and old crank and the old BB to compare. I just hate getting all excited on the way home and then finding out I can't use the part. It's the most annoying and depressing feeling. Haha.

  9. #9
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    Yeah it's a sad fact of a lot of bicycle parts

    Quote Originally Posted by ltran
    In reply to Unemployed_mechanic response. Thanks, I will go back to the LBS and bring both the new and old crank and the old BB to compare. I just hate getting all excited on the way home and then finding out I can't use the part. It's the most annoying and depressing feeling. Haha.
    Lack of standardization. If ever there's an upportunity for compatibility problems, assume there will be and research appropriately. It will save many a headache down the road. But it's getting bet, really... Back in the 60's there were somthing like 5 different "26 inch" tire sizes (all had different bead seat diameters; 26 x 1 3/4" did not equal 26 x 1.75). Now there is only one in mainstream use.

    -R

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