Ever seen a BB cup do this before?

[yoothgeye]

I'm tearing down a 1988ish Mongoose Decade BMX for a build off at vintagebmx.com and when I popped out the BB cups I found this!



I've never seen one do anything like this before. What happened? This was on the drive side, the bearings seem fine and the crank was correctly adjusted and spun just fine (1 piece). So weird.

Here is the build thread on the bike: viewtopic.php?f=56&t=60450

[509clunk]

Bottom bracket was way to tight!

[yoothgeye]

Bottom bracket was way to tight!

Yeah, but how would the bearings have survived this? Could've been old damage I guess (newer bearings maybe).

I was wondering if the crank was out of adjustment (way loose) and someone jumped it and landed with their weight mostly on one pedal it might have torqued it enough to one side to do this?

[snydur]

yes, and only because ive been the sourse of that damage before landing off a jump or bunnyhop wrong. i bent my crank at the same time and cracked the cups nearly identical to what you have there. its odd, because they always have cracks and chips missing on BMX bikes when i rebuild thim, id say 3/4 of the time. i guess its the signature of someone who rides really hard

[c.p.odom]

Seen it hundreds of times. Basically it is loose and abuse. Remember these cups are low end parts made from pressed sheet metal then hardened.
A thousand years ago when I worked with the Diamond Back Team I would occasionally install pre-war Schwinn cups on team bikes. These are machined from billet Cro-Mo and last forever.

[Rat Rod]

Seen it hundreds of times. Basically it is loose and abuse. Remember these cups are low end parts made from pressed sheet metal then hardened.
A thousand years ago when I worked with the Diamond Back Team I would occasionally install pre-war Schwinn cups on team bikes. These are machined from billet Cro-Mo and last forever.

Funny how a small tidbit of info can be so cool.