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Ch-2n bottom bracket
#1
I have a kona smoke and want to upgrade the bottom bracket to a shimano un54.

I removed the original bottom bracket which has no sizes written on it just ch-2n (i think its chin haur).

I measured the shell of the frame which is 68mm and the length of the spindle is 119.7mm.

My problem is that the spindle length doesn't appear to be a standard size the un54 does 118 or 122.5, will any of these work.

I have had a look on the drive side and there is a fair size gap between the crankset and the frame so maybe could go for the 118mm?

the spindle also is asymmetrical and is slightly longer on the drive side will this affect what size i need to order.

sorry for so many questions but this has stumped me as i am a newbie just wish it had been a standard size.
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#2
(04-19-2011, 03:12 PM)contender1 Wrote:  I have a kona smoke and want to upgrade the bottom bracket to a shimano un54.

I removed the original bottom bracket which has no sizes written on it just ch-2n (i think its chin haur).

I measured the shell of the frame which is 68mm and the length of the spindle is 119.7mm.

My problem is that the spindle length doesn't appear to be a standard size the un54 does 118 or 122.5, will any of these work.

I have had a look on the drive side and there is a fair size gap between the crankset and the frame so maybe could go for the 118mm?

the spindle also is asymmetrical and is slightly longer on the drive side will this affect what size i need to order.

sorry for so many questions but this has stumped me as i am a newbie just wish it had been a standard size.

I've opted for the un54 68mm x 122mm as i thought there would be less chance of the inner chainring fouling on the frame, hope it works.
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#3
Chain line might be an issue. BB length always is dependent upon how the crankset is matched with it. You may be good with 122mm but could be off as well. Those who know much more than me can perhaps chime in.
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#4
The chances are that the UN54 will be symmetrical so will put the chainrings nearer the chainstay if you get the 118mm size.
Obviously this will also move the other crank away from frame.
I like to go with the smallest BB I can and have used a spacer behind the BB to offset it to the right giving the chainrings a bit of clearance.
Ride hard or ride home alone!
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#5
Fitted the 122mm cartridge and it works fine. all gears still working perfectly
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