Just smang it.
French BB Questions.
I'm helping a friend a bit with his first fixed gear conversion and the frame he decided to use is an old Peugeot. I feel a bit like the blind leading the blind here because his bike has a french threaded bottom bracket. He bought a new french BB and is now looking for a single speed crankset. Will this unique/obsolete bb affect what kind of cranks he can use? This is the crankset that would meet his needs best as far as price and features go. Would it be usable?
If the original cups are still usable, all you need is the proper spindle for your chosen crank. If not, Velo-Orange offers a modern cartridge bottom bracket with French threads.
They also offer a French thread headset, should that need replacement as well.
The cranks will work. The real question is spindle length. The spindle length effects chain line, and is very important of a fixed gear so the chain will stay on. Most single speed cranks need somewhere in the range of 109 to 111mm spindle lengths. You can usually be off by a mm with little to no effect, so a 110 is usually a good bet. Check with the crankest manufacture for what spindle length they recommend.