Bicycle Mechanics - Replacing 68mm BB on 70's bike

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lostech
02-11-08, 01:23 PM
Hi everyone,

I've got an old road bike of the brand "American Arrow". It apparently was made in Germany, and I think it is from the 70's. So I've got a problem with the left crank, the cotter pin broke. After reading about the tools you need to maintain cottered cranks properly, I think I want to replace them with uncottered cranks, esp since the old crank arms are rusty. From my research it seems that I will need a new bottom bracket. So,

a)
I measured the bottom bracket shell, and it's 68mm wide. It seems that that's generally going to use English threading, but since it's an old German made bike I'm not too confident. Does anyone know about this? I did check Sheldon's site about bottom brackets, but nothing about Germany..

b)
I want to turn this bike into a 3 speed, so I'll just want one chainring. I would love any advice as to what kind of bottom bracket to get, (square or splined). I want a cheap and easy-to-work-on setup, I don't care about weight.

c)
Is it possible to replace the 'axle' with a square tapered one (I don't know what it's called, the piece that spins inside the bottom bracket?) without replacing the whole bottom bracket? Or is this just a mess I don't want to get into?

Thanks for any help!

dobber
02-11-08, 01:32 PM
It should be possible to use a modern bottom bracket in the frame, the question is what was originally there to begin with.

This might be a case for a trip to your LBS for some helpful advice. Or at least some photo's of what you've currently got.
tellyho
02-11-08, 02:09 PM
I just did the three speed conversion on an old mtb frame. Your first step is to figure out what crank you're going to use. If it's the original crank, you will probably need a shorter spindle, and that's a guessing game. If you buy a SS specific crank (like Bulletproof, Origin 8, or other higher-zoot options), they will give you the correct spindle length for a standard chainline - somewhere in the 48mm range. If you go this route, you will definitely be able to space and dish your Sturmey Archer (I'm assuming) hub to match the chainline. I recommend square taper, as there are lots of old cranks to match, and many new SS gear is still square taper.

Replacing the axle might be possible, but it's a bit of a guessing game too. The Classic and Vintage guys might know more about your setup. I suspect it's English threading.

If you buy a used crankset (old road) on EBay or CL, you should be able to find the right spindle length on Sheldon's database.

If you have any questions about cable routing, etc, shoot me a PM. I love my 3 speed setup.