I recently bought a 48 schwinn straight bar to do a rat build. When I put the bottom bracket cups in they just drop in, no forcing them, and they will turn. This can't be right? Can it? They are just standard generic brand cups. I did try a second set, and the same thing. Do I need schwinn specific cups? The bottom bracket doesn't look damaged or out of round. I'm at a loss. Any help would be greatly appreciated. I'm not familiar with vintage frames and I know even less about Schwinns, but I love the look of the frame and hope that it's usable.