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I'm re-building an old Italian Bottecchia mountain bike which has Italian BB shell (70mm) and the previous bottom bracket was a square taper with 130mm spindle (measurement confirmed via calipers.)

I taken from an old Specialized (68mm shell) a Shimano fc-m341 crankset that I want to install in my new bike. That crankset was mounted with a shimano es-25 121 mm long.

My question is: which octalink v2 bottom bracket should I buy to fit my crankset on my project? I know I need an Italian threaded BB, but should I buy a 130mm, 121mm or 118mm spindle?

Due to the wider shell, I don't know if I have to buy a 130 mm as the previous square taper was, or a different size.

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  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Gary.Ray ♦
    Commented Apr 29, 2019 at 23:15

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The spindle length depends on crank and chainline (distance from center of top tube to chainrings). In road bikes the chainline is almost always around 43 mm (exception being boost spacing), so the safest bet is to pick the same spindle length as on the bike where the cranks came from.

Different cranks may have different chainline on the same spindle.

If you can reassemble the original bikes, you should be able to measure the chainline on both of them so that you can see if you need to change the spindle length.

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  • OP's working with a mountain crank in which the chainlines are 47.5 or 50. And the spindle width is more directly tied to the specific crank, as you state. In this reference the correct spindle length is absent for the specific crank.
    – Jeff
    Commented Apr 29, 2019 at 22:39
  • Good point, I somehow just associated Italian thread with road bikes. The rest should be the same, just check that there is room if the chainrings with new crank are larger than old ones.
    – ojs
    Commented Apr 30, 2019 at 5:24

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