Curious BB cup failure
 

Not sure how this happened, It likely came out of a bike I stripped but none of them had any damage or distortion of the BB shell.

Who knows, it may have even worked well enough, cup-and-cone bearings are wonderfully tolerant.

https://cimg1.ibsrv.net/gimg/bikefor...f6e9262056.jpg

https://cimg2.ibsrv.net/gimg/bikefor...75aba3e5a0.jpg

By chance(?), I had a Stronglight fixed cup break in that fashion, a very long time ago.

It was my fault, thoiugh. I had allowed the pitting in the race to occur to a significant degree, although I don't recall the exact extent. The cup cracked when I was out for a bike ride, when I stood on the pedals to leave an intersection. It's a very weird experience to have a bunch of ball bearings shoot out of the BB and some end up in your shoe! :)

For me, it was a memorable lesson to keep on top of the condition of all bearings and cups and cones on the bike, and replace them when they start to show wear.


Steve in Peoria

Had the same thing happen to a friends bike recently. Clue was the cup would just not stay tight! Took crank off and tightened it right in 2! Fun getting the remaining threaded part out of the BB!

Looks like it might be a left hand thread.
Maybe somebody tried to remove it to the left and decided to stop just before it snapped?
I bet it was easy to turn right after that.

A long time ago I had this exact failure with a Gipiemme bottom bracket - drive side, Italian thread. The BB was stock on a relatively new bike and had not been touched. Root cause: the quality of the rest of the Gipiemme components on the bike were not up to the standard of the contemporaneous Campagnolo parts. That is putting it mildly.

Related cause: given the Italian threads on the drive side, assemblers would be motivated to install them - tight.

I found the same failure on my Huffy's drive-side fixed cup after only a few rides.

The bearings would develop play after each ride, though in part due to the bearing surfaces all yielding to the pressure of the rolling balls. This within two weeks of purchase!

I ended up replacing the suspension fork and half of the remaining components. Original cranks, levers, headset, bars, and front derailer are the sole remaining survivors, with the brakes being among the worst components needing immediate replacement due to pulsing rotors and deafening screechiness.

Before:
https://cimg9.ibsrv.net/gimg/bikefor...04b80f989c.jpg

After:
https://cimg6.ibsrv.net/gimg/bikefor...d4967fe6cc.jpg