Hello All,
I am trying to upgrade a very old cheap road bike (honestly not sure why, but it has been a fun project so far). I basically and doing it bit by bit and the time has come for me to get a new bottom bracket / crankset. But for the life of me I don’t know what type to get, as there are no internal threads and I can’t seem to find any without them. Should I just use the old one? The problem with this is that the new front derailleur doesn’t seem to have enough “range” to shift between the gears, as well as the weird metal “protector” thing outside of the gears. Does anyone know which type of bb / crankset I should look at? Thanks for all your help.
by b1g_1ke
3 Comments
That is an Ashtabula type crankset.
~~They used to make an adapter for higher quality BB but it cost $40 in the 90s. You probably would have a hard time finding one now. Perhaps if you have a friend with a lathe. ~~
Someone in another reply has a link for an adapter.
You have an American bottom bracket. There is an adaptor available to use a standard BSA/euro bottom bracket, so that you can fit a regular road crank, but there might be other fitment issues, but it would probably work fine. It’s also possible to use a bmx crank that has an American bb option.
You can get an insert that holds a modern threaded square taper bottom bracket. This is sometimes called an “American-to-Euro” bottom bracket adapter, because back in the day when Schwinn was king threaded bottom bracket shells were seen as a feature of high-end European bicycles (while most US bottom brackets were for one-piece Ashtabula cranks, like this bike had).
Here’s an example. Definitely verify the measurements of both the adapter and the bottom bracket you plan to install before purchasing anything–I did not actually check to make sure this one will fit your frame, it’s just intended as an example.
[https://www.porkchopbmx.com/euro-to-american-bicycle-bottom-bracket-adapter-si.html](https://www.porkchopbmx.com/euro-to-american-bicycle-bottom-bracket-adapter-si.html)
In addition to the adapter, you’ll need a bottom bracket, but it’s a *very* good idea to think through your whole drivetrain, including cranks, chainrings, etc., because the bottom bracket not only needs to fit the adapter but also needs to be the right width for the shell and needs to have the right spindle length to put your crank’s chainring(s) in the right spot to have a decent chainline (that is, it/they have to be in the right position relative to the cog(s) on your rear hub).
EDIT: I’d also say you should STRONGLY consider reinstalling the existing cranks and bottom bracket and simply fix whatever the problem is with your front derailleur. Not only does an adapter like this require pretty much replacing the whole drivetrain, the end result just won’t be as strong as the original, and bottom brackets take a lot of abuse. Those adapters are cheap aluminum and they’re just adding a lot of parts that can flex, creak and fail to a part of your bike that has to withstand considerable forces.