Replacing BB, size confusion

Fishheads Posts: 3
edited October 2010 in Workshop
Looking for a bit of help with changing a old BB.
I have a road bike from the late 80s and I want to change the BB because it’s just generally old and heavy.

I'm not massively knowledgeable about bikes but I've learnt to do everything and change every on my bike as I've gone along but changing the BB really stumped me.

I thought it would be a straight forward job but I can't find any sizes on the BB at all, I'm not totally comfortable about measuring with a tape measure and getting exactly the right measurements etc.

It’s got square tapered ends with one being slightly bigger than the other, here is a picture with the measurements on it


I'm thinking maybe I should keep the spindle and get different cups just to save the hassle??

BTW I'm pretty sure the threads are English and the shell? is 68mm.


  • Butterd2
    Butterd2 Posts: 937
    Buy a 120mm shimano BB they're cheap and pretty bombproof. Should fit fine, but if not you haven't really lost much, sell it on and buy a slightly longer one. You'll probably want to buy the BB tool also otherwise it will be a pig to fit.
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  • Butterd2 wrote:
    Buy a 120mm shimano BB they're cheap and pretty bombprooft.

    I would consult a competent shop to buy your bottom bracket from.

    You need one that preserves the existing chainline - note that a lot of modern cartridge type bb's are symmetrical, unlike your old one - and you need one to match your chainset. I say 'match' beacause you get a Japanese taper (JIS) and European/ISO taper.

    I might be inclined just to replace the cups.
  • Steve2020
    Steve2020 Posts: 133
    I would recommend a cartridge BB - you'll never have to think about it again (probably).

    It should be straightforward to get one to fit. Taking the axle to a bike shop is the easiest way.

    You're unlikely to save much weight though, whichever option you go for.