Bottom bracket spindle length

Thomson0
Thomson0 Posts: 49
edited February 2012 in Workshop
I have stripped my steel bike to repaint it and while I am at it I am going to replace things like the jockey wheels and rear wheel hub bearings I have decided that as I haven't a clue how old the bottom bracket is I might as well replace the bottom bracket. Thing is that it's a double chain set and the inner ring is very close to the chainstay (2-3mm) and I was wondering about the length of the spindle it's a shimano UN52 bracket which appears to be discontinued. This brings up a couple of questions,

1. Can I replace the bracket with a UN55 Bracket?

2. The spindle length is 118mm so if I replaced it with a 122.5mm or 127mm spindle length mean that there would be a bit more clearance?

Comments

  • Wirral_paul
    Wirral_paul Posts: 2,476
    Have a look at the following - hopefully you will find your chainset on the list and this will tell you the correct size. I wouldnt worry about the clearance so much if it isnt catching, its the chainline that you need to ensure is right. This should automatically be correct if you use the standard BB for the chainset

    http://sheldonbrown.com/bbsize.html
  • Twostage
    Twostage Posts: 987
    Thomson0 wrote:
    1. Can I replace the bracket with a UN55 Bracket?
    Yes.
  • Thomson0
    Thomson0 Posts: 49
    Thanks for the info I have checked the chain set its not one of the big brands it just says custom on it so I think I will order a new UN55 bracket and try the 122.5 sprocket it's only 2mm larger on each side so I am assuming it will give a small amount of extra clearance.
  • keef66
    keef66 Posts: 13,123
    Just beware if you go for too long an axle, your front mech might not be able to shift the chain far enough to reach the big ring.

    Found out that was the problem when restoring an old Peugeot with my son. A previous owner had fitted a UN 52 BB with too long an axle. Not helped by the fact that it has a Veloce chainset which is designed for ISO square taper rather than the JIS of the Shimano BBs. DT friction shifters struggled to get the Double front mech to reach the big ring. Swapping for a shorter Shimano BB sorted it easily.
  • Thomson0
    Thomson0 Posts: 49
    I got a UN55 with 122.5mm axle from highonbikes delivered this morning i am finally going to get round to painting the frame and forks tomorrow so when i get everything put back together I will soon find out if I have made a mistake. I will let you all know how I get on. Thanks again for all the info.

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