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Crank Selection to Match Bottom Bracket.
#1
Hi.

I'm replacing the BB on an old steel frame I have. The dimensions are: 118mm axle / spindle length and 68mm BB shell.

I want to buy the replacement online, but also want to buy a set of cranks as well - what measurements are important when I choose cranks? - If the spindle interface is "square taper" obviously the crank arm must be able to fit this.......is the spindle length to be considered also?

Can anyone suggest a good BB / crank / chainring combo? - I'm hoping to build up a single speed commuter. Not wanting to spend too much, but must be durable!

Thanks in advance for any help or suggestions offered.
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#2
To some degree there is a matching needed between crank and spindle length. But if you're converting to single speed you have an added consideration which is chain line. If possible, I would recommend buying the crank you want, loosely mounting it to the existing BB and checking to see where the crank lines up. Then you can adjust spindle length to suit whether you need to move the crank in or out.
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#3
Thanks lot for the reply DaveM.

All I have right now is frame and fork. Have removed BB, which is stuffed and looking to replace etc. I currently have no other parts (apart from a headset) for the bike.

Can I assume that a square tapered spindle is a common spindle end that will fit a wide variety of cranks?

To correct the chainline - is it possible to get spacers for the rear hub? or do I need to get rear hub spindle length correctly aligned with the front cog?

Sorry for a question loaded reply, but I appreciate your help.

Cheers.
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#4
All square taper stuff is compatible except for some obscure Japanese NJS track stuff. But you won't normally see that unless you go looking for it.

You can definitely re-space the real axle, so you don't have to get the BB perfect.

Probably safe to get a new BB with roughly the same spindle length and then do any tweaks later. But there are a lot of variables with cranks, frames, wheels, etc. So hard to promise everything will work on the first try. Note that if you have a crank, you can just loose fit the old BB into the frame so you can get a rough idea where the crank will end up. But I understand it would be frustrating to have to do several separate parts orders.

Here's a primer on doing the conversion which might have some useful tips for you: http://www.cicle.org/cicle_content/pivot/entry.php?id=1572
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#5
Thank you Sir!!

You've been a big help.
  Reply
#6
Sorry to dig up an old forum, but I am also restoring an old steel bike - it is from the early 80's.

Is it possible to put in a new off the shelf BB or do I have to find a vintage unit from around that era?

I am putting old campy gear on the bike, and the vintage BB's seem to sell for over $100 where as I can buy a Campy Veloce for around $30 and expect I would have a lot less problems as it has sealed bearings.
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#7
Do you know the make of the frame?
Some BBs differ depending whose make the frame is.
ie Raleigh had their own threads. Italians and French also differed.
There is usually no problem with changing to a more modern sealed version.

See Sheldon Brown:-
http://www.sheldonbrown.com/gloss_bo-z.html

scroll down to BB section!.
Ride hard or ride home alone!
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