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Choosing replacement bottom bracket
#1
Hello there everyone im a newbie to the forum hoping someone could give me some advice.

I have an old claud butler urban 200 which i plan on slowly bringing back to life, i have managed to remove the bottom bracket 1st one ever which is a chin haur CH52-68 122 BC 1.37 X 24T now i was thinking of replacing it with a shimano sealed bb.

My plan was to take it to work and measure the diameter across the threads and the length on the spindle with a vernier and buy one of the same dimensions.

What im not sure of is i will also be replacing the crank as well as the teeth are badly worn, as im replacing the crank as well will this mean i will have to be careful of the length of spindle on the bb i order?
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#2
Yes a different crankset could require a different bottom bracket length.
Ask at the place that your going to get the cranks from or, if you know the model number, possibly check out the manufacturers website.
From your current BB we can deduce =
68 (mm) is a standard length for the BB shell. That's the part of the frame that the BB screws into.
24T is probably the TPI (threads per inch of the BB) and again that's a standard.
122 (mm) will be the overall dimension of the spindle length and it's this dimension that is the important one that could vary.
There is, however, 2 general types of crank standards.(ISO or JIS) The difference is in the length of the taper on the spindle ends.
So try and keep to the same standard for the BB and crank arms.
See Sheldon Brown for a comprehensive information page.:-
http://www.sheldonbrown.com/bbsize.html
Ride hard or ride home alone!
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#3
Thanks for the reply, I think i understand better now.

Now i was thinking of buying a shimano un54 68 122 http://www.chainreactioncycles.com/Models.aspx?ModelID=17473

and maybe a Suntour CW8-XCC-T208 A BIG Square Taper Chainset http://www.chainreactioncycles.com/Models.aspx?ModelID=41902

The problem i have is that it doesnt indicate what spindle length this crankset is compatible with on the website selling it and they are no longer listed on suntours website possibly discontinued so i guess i would have to contact chain reactions?
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#4
(01-06-2011, 05:22 PM)contender1 Wrote:  The problem i have is that it doesnt indicate what spindle length this crankset is compatible with on the website selling it and they are no longer listed on suntours website possibly discontinued so i guess i would have to contact chain reactions?

The spindle length required is determined by the crankset AND your frame geometry. If you measured where your sprockets are currently with respect to the frame (seat post is a reasonable datum); then after you get your new crankset you can measure to determine the spindle length needed.

Practically speaking, a variation of a couple of millimeters either way will not make a difference as long as the chain does not hit the frame or wheel.
Nigel
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