hi, i acquired an old royce union folding 20" wheeled bike. my gf wants to use this as a rain bike, but the BB axle is bent, making pedaling weird.

i was wondering if it is possible to swap out the cottered BB for a modern square taper? what needs to be done to make this modification?

thanks!!!! -daniel

You might luck out and find a tapered axle that will fit. The diameter and bearing size need to match. Most taper axles use a 1/4 inch ball. Might take a try or two to get the chainline right. Go to the oldest shop in town, they are most likely to have the old axles in stock.
If it will not fit your cups, and the BB is English, you can get a YST BB kit cheap. It has cups, lockring and bearings, so you still need an old taper axle.

I found that you can swap out old British cotter crank BBs with 1980's vintage Schwinn BB cotterless cranks. This is being pulled from two year old memory, but I think it was a Schwinn Sport that I used. I did it on two bikes and it worked perfectly.

I replaced the BBs on a Hercules ten speed and a Raleigh Grand Prix ten speed. Both had cottered cranks and both were from the 1970's. Like I said, I replaced them with cotterless BBs from made-in-Taiwan Schwinn Sports.

Everything fit perfectly with no need for alterations or modifications.

great, thats exactly what i wanted to hear, bc i have a bottom bracket from an 80s road bike kickin around! thanks a lot guys!
-dan

NOOB ALERT! NOOB ALERT!

What's the difference between cottered and cotterless cranks (apart from the lack of cotters, whatever they are)? What type are modern three piece cranks?

Your Royce Union should be English threaded so you should be able to do the switch w/o too much hassle. Any older bike that's not a collectible can benefit greatly from this swap.

Jonny: Both types are piece cranks. Modern (been around awhile though) is cotterless. Cottered cranks are usually chromed steel (aluminum has been used but rare) and the cranks are held to the BB spindle by threaded bolts and nuts called cotter pins. They pass through the crank arm where it fits over the spindle and press against the spindle holding the crank arm in place. For a long time they were standard on bikes world wide (US made Schwinn the major exception). Pretty much extinct today except for kid's bikes and some real lowliners.

British/ISO BB threading and a 68mm wide BB shell open up a world of possibilities, including a modern sealed bearing cartridge BB. You should be able to find something suitable, although you may have to experiment a bit with spindle lengths. This is where a cooperative and sympathetic local bike shop is invaluable.

I have converted numerous bikes of the 1950s, 1960s, and early 1970s from cottered cranks to cotterless.