In a previous post, I asked a question about a weird bottom bracket on a bike I’m replacing, and learned that it is some approximating an ashtabula bottom bracket. However, in disassembling this weird bottom bracket I discovered that one of the cups is cracked and has a groove on the inside – so the bearings don’t do their job. I’ve always known something was up, as the crankset was a little off-kilter for the time I used it (but I dealt with it).
Any idea if this size is a particular standardized kind of bottom bracket cup that I can get easily online? Or do I need to have a replacement machined?
by HuaFeng36
2 Comments
It’s an Ashtabula type frame but with cottered cranks. Assuming you’re replacing the cranks while you’re at it, you can use[this Truvativ adapter](https://www.universalcycles.com/shopping/product_details.php?id=22473&srsltid=AfmBOor2KP4YrqN0Fa0Y1macSG2ikoBil789a_lNHP7iCApNToJmrJHx) to use any normal BSA/English threaded bottom bracket that matches the new crank
Based on the cottered-ness of the cranks, this looks to be a Thompson/Thun 40mm bottom bracket.
[https://classic-cycle.com/Drive/Hub-Crank-Chainwheel/Parts-and-others/2326/Thompson-Tretlager-Keil-Innenlager](https://classic-cycle.com/Drive/Hub-Crank-Chainwheel/Parts-and-others/2326/Thompson-Tretlager-Keil-Innenlager)
[https://www.radgeber-brieselang.de/Innenlager-Thun-Thompson-40mm-Vierkant-Welle-133mm-NOS](https://www.radgeber-brieselang.de/Innenlager-Thun-Thompson-40mm-Vierkant-Welle-133mm-NOS)
There’s one on eBay in Germany for US$38.66 but it says “1 9/16” for the size (which is 40mm in fractional inches). This sub doesn’t like eBay links so you’ll have to find that on your own if you’re interested.