Updating Older Bottom Brackets
Phil Wood & Company makes retaining rings for all historic threaded bottom bracket sizes except for Ashtabula. Therefore, Phil Wood cartridges can be fitted to just about any type of bottom bracket shell. Any bottom bracket cartridge that allows removal of both cups can also be mounted with the Phil Wood rings and tools. In particular, the Shimano UN-71 and UN-72, Campagnolo Chorus/Record 2006 (all obsolete now), and the Tange/IRD square-taper bottom brackets can have both cups removed, although the Tange diameter is 2 mm larger than necessary, and so some filing of the mounting rings would be necessary. This solution is very popular for bikes with Swiss, Raleigh, or Chater-Lea bottom bracket shells.
In addition, most bottom bracket shells of the 33.6-33.9 mm size can be 'tapped out' to the larger Italian 34.6-34.9 size in situations where the threads are irreparably damaged. Before this is done, glues such as JB Weld or Phil Wood Red or Green Retaining Compound should be tried. If all else fails, there are several types of replacement bottom brackets that press-fit or self-tighten into the BB shell, for cases where threads are destroyed. These bottom brackets require further facing or machining of the bottom bracket shell, and it is worth comparing the cost of having a whole new bottom bracket shell brazed in (for a steel frame), especially if the frame is in need of a re-paint anyway.
Another alternative for damaged or uncommon bottom bracket updates is threadless bottom brackets that work by expanding against the existing bottom bracket threads regardless of what they are. This can offer a relatively cheap option. Inexpensive French bottom brackets are now back in production as well.
Read more about this topic: Bottom Bracket, Sizes
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