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Cross threading
#1
Hi,

Is it possible to damage the threads of the bottom bracket shell while undoing the BB?

I'm pretty sure the bike shop would have done it while putting the bike together, but if I can check it's not possible (very unlikely) to damage it while lossening then I'll feel more comfortable complaining til they fix it.


Thanks
Oggy
  Reply
#2
It is not possible to cross thread undamaged threads during removal until the last thread or two, and then only by leaning on the male part so that it bending with respect to the housing. In the case of a thread the size of the BB, you are talking way over 100lbs of leaning force.
Nigel
  Reply
#3
Not sure why you are asking this. Is there a problem?

Cross threading occurs when nut is put on crooked and damages the threads. If the nut is put on properly removal will not damage the threads.
However on badly rusted pieces removal can shred the threads. So pre soaking with penetrating oil sometimes for several days and using heat on the nut to expend it helps.
Never Give Up!!!
  Reply
#4
Yeah; I expanded the definition to damaged threads.
Nigel
  Reply
#5
I was asking because I had real trouble removing the drive side BB cup and when I came to put it back on it wouldn't thread smoothly and after checking, the BB shell thread is damaged.
Now thinking possibly from over tightening.

I didn't think undoing the cup would cause the damage but wanted to check first so I don't get fobbed off by some guy who should know what he's doing (but doesn't) when I take the bike back and they try to say I did it when taking the BB off.

Thanks for your replies.
  Reply
#6
I doubt the threads could have been damaged from over-tightening. But they definitely could have been if they put the cup in wrong, realized they were cross threading, backed in out and then got it in right.

But two questions
- Is this a new bike?
- If so, would the shop have installed the BB themselves? All stock bikes come from factory with BB installed.

If it's not a brand new bike, the threads could have been damaged a long time ago.
You couldn't have damaged them removing it unless you did something really weird, but I think it may be hard to know/prove they did it.

Compromise may just to get them to chase the threads with a BB threading/facing tool. If the damage to the threads was fairly minor, it should cause any issue. But again, I'm not sure of the bike/shop's history so...
  Reply
#7
I damaged some threads when I had to cut out a corroded BB cup; my favorite shop, Wheel Away, charged me $10- to chase the threads and face the BB with their $300- Park tool set. To me, a great bargain. I doubt that they'll ever pay for the tool set.

If Wheel Away had caused thread damage to a BB shell, they would have chased the threads, and the customer would never know. The BB would go in and out super smooth, and the threads would be greased. A good shop will make sure that the threads are not damaged before the bike leaves their care.
Nigel
  Reply


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