Hi,

I have a 80-90's Concorde race frame with a vintage Dura Ace Crankset. The other day, my crank arm started to unscrew itself from the BB and ultimately came off completely. The crank arm has a crack in the arm which might be causing it to unscrew. However, I'm not sure the BB is broken or if it's supposed to look like this. It looks like one part of the bolt, the "thread stem" is merged/a part of the bottom bracket and then theres just a small nut to screw back.

I have tried to screw the crank arm back with help of the nut, but after a couple of miles it goes back to keeps unscrewing itself.




Is this bottom bracket also broken or is this some niche type of crank set? Or can I extract the "threaded" stick that comes out of the BB, or is this an integrated part of the BB?