BB threads in poor condition.

[Globalti]

Changing the BB on Gti Junior's new (old) bike, ali frame. When I removed the drive side BB cup it actually tightened up and as it came out, a nasty-looking hair-thin sliver of swarf came out with it, several inches long. I had no choice but to keep going, knowing I was probably damaging something. Now the new cup won't screw in cleanly, it galls and gets stuck and when I remove it, little pieces of swarf come out. I know it's not cross-threaded because I've replaced the LH cup as a guide for the BB axle. I have tried cutting two slots across the threads in the old cup to try to help it clear the threads in the frame but I'm making no progress and fear I'm dangerously close to ruining the frame. It's my impression that small pieces of aluminium are actually melting and re-depositing in the threads under very localised friction heating. Anybody else been in this situation and found a way around it?

I'm going to take it to the LBS where it was bought this week to ask the bloke to clear the thread out with a proper thread cutter. No point in going any further with my limited resources.

 

[yello]

Anybody else been in this situation and found a way around it?

No, never. The only time I've had swarfs is when I cross threaded a bb putting it in.

I'm going to take it to the LBS where it was bought this week to ask the bloke to clear the thread out with a proper thread cutter.

That'd be what I'd do, and indeed what I did when I cross threaded the bb! Took the lbs all of 20 minutes to rethread and cost me €10.

Some tasks I leave for people with both the knowledge and the proper tools. I've always assumed a reaming tool was quite pricey but I don't actually know.

 

[tyred]

Stick a "threadless" cartridge BB in it. Mine cost about £12 from Parkers of Bolton.

 

[Globalti]

Reaming tools are indeed expensive - a couple of hundred quid.