Measuring Bottom Bracket Size

rb25

Hi.

I have an old frame from a BSA Crusader bike. I have stripped everything off the frame - peddles, inner bottom bracket, wheels, handlebars, etc.

I'm hoping to replace the peddles with different type that are easier to remove and fit back.

What's the correct way to measure the correct size bottom bracket so I can replace it with an adapter?

macnab

Have a look at this:

http://www.sheldonbrown.com/bbsize.html

rb25

macnab wrote: »

Have a look at this:

http://www.sheldonbrown.com/bbsize.html

Woah! Confusion rains.

Lumen

There is no such thing as an "inner bottom bracket". I think your question would also benefit from use of the word "chainset" or "cranks".

What exactly are you trying to do with the pedals?

rb25

Lumen wrote: »

There is no such thing as an "inner bottom bracket". I think your question would also benefit from use of the word "chainset" or "cranks".

What exactly are you trying to do with the pedals?

Forgive my ineptitude on precise terminology. There's the bottom bracket that is part of the frame and the inner bracket that is the chrome piece that fits inside the bottom bracket of the frame. This chrome piece is not part of the crank so not sure what it is called. I thought I may need to replace this piece too seeing as I want to replace the whole of the peddle and chainring mechanism.

The crank and peddle arms were cut to remove them from the frame because of rust so will need to replace everything that goes inside the frame.

I'm trying to make a fixed gear bike from this old frame.

piston

You will have a cup and cone bottom bracket, almost certainly with cottered steel cranks with a swaged chainring(s).

Assuming it isn't ridiculously worn, all this will go back together again and work perfectly for many years if done properly. This is probably what I would do. The tip with cotter pins to is to file them to reduce the angle of the taper and then press or hammer (support the opposite side of the crank with a block of wood or something to avoid hitting directly on the bearings) them into place. The mistake people make is just sticking the pin in and then tightening the nut. The nut's only purpose is to hold the pin in place after it's been forced into place tightly. The thread isn't strong enough to pull the pin correctly into place and if you just do this, you will have loose clicky cotterpins and possibly damaged cranks.

If you do want to change to square taper, measure the width of the bottom bracket shell without the cups installed as a first step and hope it is 68mm (if it's 71mm you probably have Raleigh non-standard 26TPI threads - Raleigh owned BSA by 1970 - much badge engineering went on).

If it's 68mm, then you can use basically anything you like, the tricky part will be working out the correct width for the correct chainline. You could buy a separate square taper BB axle and re-use the original cups but you may as well fit a sealed unit for ease of maintenance.

If it's Raleigh threads, re-using what you have is probably the best option unless you want to get creative. You probably should be able to find a suitable separate BB axle of the right width and re-use the Raleigh cups (and they were of a quality standard you just won't buy today) and I also think they might be conversion kits available now for Raleigh BBs.

kumate_champ07

if all else fails you can use a threadless bottom bracket

http://www.velodromeshop.net/index.php?p=product&id=2365