Converting a cottered crank bike to square taper?

stickman

Can it be done? I'm referring to my Raleigh.

meagain

Can't think why not! At simplest, just a replacement axle. More expensively, a complete new b/b (though depending on age may need to watch out for Raleigh-specific threading on the cups). Oh and new cranks obviously!

Hell below zero !

Yes, the threads of the bottom bracket are what matters, being a Raleigh they are English so all you need to do is remove the old cottered chainset and bottom bracket and fit a new tapered English bottom bracket. Note Italian and French threaded won't fit as they are threaded differently . The critical thing is to get the right length of axle for the chainset you are going to use ! Also the taper of the new axle needs to suit the chainset as well.
Shimano a Japanese taper, Campag a Italian taper. Other chainsets check whats needed !

stickman

Thanks for the replies.
Is it an English thread that ordinary Shimano etc. bottom brackets have?

nicklouse

stickman


have a read http://www.sheldonbrown.com/gloss_bo-z.html#bottom
as you can see some Older British-made Raleighs, especially 3 speeds had their own set up.

but some quick measurements will soon sort that out.

stickman

Thanks.

Dickie

STD english 24tpi, Raleigh 26tpi. Does depend on year, though it is obvious when you compare cups.

stickman

Thanks. It's approx. 1990. I think.

Update: I checked the gear hub and it's dated 1991.

Dickie

Stickman iIt should be 24tpi at that year, if you put two cups (say a shimano cartridge and your cup) together thread to thread you can see any pitch error clearly.

stickman

Thanks, that sounds encouraging.

meagain

1990 and cottered cranks?! Is it worth saving?

stickman

If I couldn't fit a modern BB maybe I would get an Archie frame and transfer the parts over to that. (same 650a wheel size)

stickman

Finally took it apart today, checked a spare Shimano cup in it and it matches. I'll go to my lbs tomorrow and hope they've got a modern bb in my size in stock.

stickman

Found out that because they fit in diffent ways that bb axle lengths are different - so is there an axle length conversion chart for going from cottered to non-cottered?

custom-freak

hello the axle length will depend on the new chainset, it will need to set the ring(s) at the same distance from the seat tube as the previous chainset, what is the new chainset that you are fitting? each one has a preffered botom bracket axle length (and specification) for perfect alignment

Cf

stickman

Thanks,
I should have updated this. The chainring is a Mighty-X 46 tooth, common to see on ebay, I found I had an old bb axle and did a mock-up, found out i'd need a 127mm which I bought and there's no problem.