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How do I determine the correct BB size needed?(7 posts)

How do I determine the correct BB size needed?Lone Gunman
Feb 17, 2002 6:10 PM
I am switching out my BB on the project bike to a cartridge style bb. The old one was a solid steel bar that is 145mm threaded end to threaded end and is the square taper type that took connecting bolts. This is for a double chainring 68mmX ???
Local pro shop would know.guido
Feb 17, 2002 6:58 PM
What brand of bike is it? The Italians used 70 mm BB shells, 24 tpi, standard threads on both sides. The English used 68 mm shells, same 24 tpi threads, and reverse threading on the fixed cup. That wouldn't be hard to figure out.

The flats on crank spindles weren't always the same pitch, however, and that's where the LBS might come in handy. They have parts catalogs that give dimensions of spindle lengths and spindle flats pitch, and they have probably replaced enough old BBs with sealed cartridges, to know exactly what you'll need.

Good luck with your re-build. I take it the old BB is shot. I'd check out the availability of an old style BB, though. I used to repair old ones from the 60s and 70s. They had loose balls instead of retainers. That would be one more ball on each side, and they lasted forever. They also spun silky smooth, because they were unsealed. The best ones were slightly overbuilt, compared to the sealed cartridges today. (Flame away, guys!)
Actually...Lone Gunman
Feb 17, 2002 7:49 PM
the old one is not shot at all, it just weighs 3.5 lbs and I prefer the cartridge style, nothing to overhaul. The bike probably has less than 2000 miles on it, a 1978 I bought it when I started college in '78 and when I got there, no one else had a bike and they/we walked everywhere. Wanting to be part of the group, I didn't ride it much except in the summer to train for soccer. And even then I didn't really know how to train to ride, 10 miles was a big deal cause I could cover it quickly. The saddle was torture, no bike shorts etc. The bike sat around indoors for all these years, was used as a trainer bike for a while, parts were pulled off and stuck in a drawer. Last summer I gave it away and found out recently about the possible faulty fork that was recalled. I managed to track it down and recover it with all it's parts stil there. I am still amazed I got it back.
Use the original!guido
Feb 17, 2002 8:59 PM
If the races are still shiney, no pits, heck, stay with the tried and true. The weight is in the perfect place, low on the bike, for handling. You won't even notice it. You want to go stock, right? There'll be plenty of aftermarket cartridge BBs around by the time you wear this one out, if you ever do. The ball bearings are bigger than sealed bearings. I'd bet they have less rolling resistance and can handle bigger loads than sealed cartridges. Greased up every couple of years, what is it, a Simano 600?, it'll go another 10,000 miles. I've only had to change-out one (Campy SR) because the idiot in the bikeshop set it up too tight when I bought the bike new. The replacement has lasted since 1987, around 15,000 miles. Will a sealed BB do that?
Local pro shop would know.Rusty Coggs
Feb 18, 2002 5:31 AM
For spindle length,measure end of taper to end of taper.Look on the cups for threading.English is 1.37x24 with a 68 or 73mm shell width. Italian is 36x24 with a 70 mm shell width. Campy cranks use ISO taper on the spindle,and oriental origin stuff uses JIS taper(shimano).
Thanks Rusty...Lone Gunman
Feb 18, 2002 6:32 AM
Already knew it was a 68mm didn't know correct length to keep drive line correct. After measuring, the taper to taper is 125mm. In taking a quick peek at a catalog, I see 122.5 and 127.5 in a 68mm cartridge style BB . If I go with a 122.5 will this make a big deal in a friction shifting setup I will be using?
122.5 will probably work fine.Spoke Wrench
Feb 18, 2002 6:40 AM
I'd use the wider one if you brush your heels on the chainstays with the current set-up. The difference is only a millimeter or so on each side. Your derailleur will never tell the difference.