I recently picked up an old bike frame for a future project. It's a mid-'70s Motobecane and it seemed to be in decent shape overall, but it did have a drive-side bottom bracket cup that was extremely stuck. The guy I got it from had tried and failed to remove it, so he just sold it to me "as is," bottom bracket bits and all. Being that I couldn't say for certain that the included spindle would work with whatever crank I'd eventually want to use, and the fact that I can never just "leave well-enough alone" I decided I'd need to make sure I could actually remove the stuck cup before I started putting any more money into the project.
I expect that (at least in part) the problem may have been that someone (whether it was the seller I got it from, or perhaps whoever he might have gotten it from) wasn't aware that the bottom bracket was Swiss-threaded and therefore "reverse" or "left-hand" threaded on the drive side. I can picture someone putting arm-breaking effort in the wrong direction trying to remove it, and only making it impossibly tight as a result.
I tried some penetrating oil and letting that soak in for a while, but still couldn't budge it. I tried heating the shell with a heat gun - hoping it might cause it to expand a little - and tried chilling the cup with an ice cube, but none of that helped either.
One thing that makes it difficult to remove a stuck cup is that the outer part of the cup, and the spanner that removes it, are only about ⅛ of an inch thick. Even when the cup is not stuck, it can be difficult to apply the necessary torque without having the wrench slip off. In this case, where the cup was truly seized up, it was near impossible. The wrench would end up slipping, and I was concerned that if that kept happening, eventually the flats on the cup would get rounded off, and then there'd be no getting it off no matter what.
So, here's how it works. The bolt with the smaller washer goes inside the bottom bracket shell, through the bottom bracket cup, with the bolt head and small washer centered in the cup. On the outside, I put on the spanner, sandwiching it in place with the large fender washer and the nut. Tighten it all down.
With the spanner held securely in place over the cup, snugged up to the edge of the bottom bracket shell, I could apply some serious torque, involving a big piece of pipe slipped over the end of the spanner to really extend the leverage. It still took a lot of effort, but I got the thing to move.
|There's the cup - with nice undamaged races.|
I hope this little home mechanic hack proves helpful to someone out there.