Bicycle Mechanics - Need help identifying bottom bracket!
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09-20-10, 11:48 AM
So I built a fixie from a pretty old frame and kept the original crank on there. After about 2 months I've decided I'm tired of screwing with the cotters, so I want to upgrade to a new crank. I'm fairly certain that my bottom bracket wouldn't be compatible with any cotterless crank, so I'm looking to replace the bottom bracket along with the crank. I've attached a photo of my current bottom bracket, I'm pretty sure I've got a "loose bearing" style, and I want to know what my options are in terms of replacing it.
Also, would I keep the threaded piece on the left of the photo with the new bb? The right threaded piece is stuck into the frame pretty well so if I can keep those that'd be good.
The crankset I was looking to get recommends a 107-110 mm JIS bb. Any help is well appreciated.
09-20-10, 12:00 PM
You should be able to get a square taper BB in whatever length you need. The thing you need to know is what thread the BB shell has. Could be English, French, or Italian. Most likely English, but not guaranteed. The left cup (drive side) will be left-hand thread (if English), so you would need to turn it clockwise to remove it. A new BB will have its own cups, so I would not use the old ones.
09-20-10, 12:26 PM
Are there any numbers on the outside of the cups? Those numbers would indicate the threading. If the threads are english or italian that would be good. If french then it may be harder to find a current bottom bracket.
French ones can be found on Velo Orange
look at Sheldon Brown's page on bottom brackets and threading, this will help determine the threading of the bottom bracket.
09-20-10, 01:34 PM
I managed to get the other cup off, it was threaded left-handed. There isn't any writing on either cup but my rough measurements suggest it fits the British/ISO diameter of 1.375" and 24 tpi off of Sheldon Brown's guide.
So would this work with the JIS crankset I mentioned? It doesn't look like it but all these conversions can be pretty confusing so I still want to check.
09-20-10, 01:40 PM
If you have a Local Bike Shop nearby, take the left (drive) side cup in and have them compare the threading to an English thread one. Then you will know for sure if it is English.
What make is the frame? That may identify the BB threading too.
Having left threaded drive side cups ensures that it's not French or Italian threaded, that leaves Swiss (rare), Raleigh proprietry or British/ISO which is by far the most likely.
The best approach would be to go with one of the Shimano sealed units, either a UN26 or UN54, they're cheap and easily available in a variety of spindle lengths and they are JIS taper.
Seeing as you're using it with a fixie, you need to pay attention to your chainline. Take a good look at the chainline spec for the crankset and choose a spindle length from that.
09-20-10, 09:36 PM
What make is this frame? The picture shows what looks to be an old Phillips bottom bracket cup, which may be the now obscure 1-3/8" x 26tpi threading. If so, your choices are limited: either reuse the old cups with a new spindle to mount a more modern square-taper cotterless crank, or use a threadless cartridge bottom bracket to mount the crank of your choice.
09-26-10, 02:01 PM
Finally got around to going to my LBS (weekdays suck for me). It's a 1.375in * 24tpi British threading, but it has a 80mm shell... so we had to knock out some of the shell that was just pressed in and get an adapter for relatively little cash so I can slap a JIS crankset on there. Thanks everyone for the help!
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