Convert a 3-piece crank to a 1-piece (Astabula) crank??
 

I know, you are probably thinking 'why the heck would anyone want to do that?' Well, I have a decent bike with a nice alloy 3-piece crank and a nice bike with an anchor (Ashtabula crank). I want to sell the bad bike with the bad crank and keep the good one, so..

-Do I need to buy a new bottom bracket?

-Do I need anything else to make it compatible?

-Can I simply swap bottom brackets, bearings and cranks from one to the other? (both are 68mm BB shells, both are very similar Schwinn 10speeds from the early '70s)


I understand that I may need to remove, swap and repress the cups into the shell(s), but can anyone confirm the difficulty/possibility of this whole procedure before I tear both bikes apart? I know basic mechanics and terminology, and I do not need info on installing the 3-piece, just the Astabula set. Thanks!

Conversion from one piece to three is possible with an adapter, but I know of no way to go the other way due to the fact that the one piece BB shell has a larger diameter than a English threaded shell.

How did you end up with a nice bike with a astabula crank? Just curious. I know I do whacky things and wonder what other people do sometimes.

Used to have a Schwinn Traveler, Lugged, made in Japan but with an 'american' BB shell..

at the time, (80's) I found a nice tubular OPC crank..

It could be a Schwinn Varsity or something similar. Varsities are heavy, but they're a nice bike if all you want is something that works reliably, in contrast to most modern bikes with one-piece cranks, which fit the "bike-shaped object" category.

As for the OP, there are a very few bikes (mainly low-end Raleighs from about 10 years ago over here) that use a one-piece crank style Ashtabula BB shell and bearings, but come with a 3-piece crank adaptor spindle that's threaded for the bearings in the same way the crank would usually be. Unless your bike with the 3-piece cranks is one of those very rare cases, there's no way to put a one-piece crank on it.

Edit: A tubular one-piece crank... wow!

Bottom brackets are so cheap you should forget all about the ashtabula crank and just buy a new cartridge. A spindle, cups, and bearings would be even cheaper. You can get both kinds for cotter pins too.

Nope. Even if you could get bearing cups that would fit in the frame (you can't) and tiny ball bearings to run in them, the crank just plain won't fit through the BB.

MAYBE.

Can you post pictures of both bikes?

If they both have the bigger American bottom bracket shell, you can swap the cranks. There are three piece cranks, with cotterless cranks, that fit an American BB. I've worked on a few thousand on rental bikes, and converted many from three piece to one piece.

An Astabula crank may not go thru the usually small bottom bracket of a 3 speed BB.