Cross Threaded Bottom Bracket
 

I have a bottom bracket that was cross-threaded once. I had the threads chased, replaced the bottom bracket and now it is cross-threaded again. How many times can a bottom bracket's threads be chased? Is it worth trying to chase the threads again? I really don't see any other option, but just wonder if I have already used up my allotted opportunities to do this and am now at the point of diminishing returns. Thanks in advance for any advice.

It's toast.
Chasing the threads can't restore damaged material, it only cleans up the threads, but they are usually shallower.
Chasing a second time is basically an act of desperation.

There may be a way to fit an insert or something to save the frame.

Chasing does not really "repair" damaged threads, it attempts to push the distorted metal back into shape but there are limits to how well this works. I would suspect that if you have had it done once and it has got cross-threaded again that trying it again would likely be futile. Are you trring to reinstall the BB which went in cross-threaded? If so, ITS threads may be damaged too and might not work even with brand new perfect threads.
If you have a square taper bottom bracket you could fit a threadless one like this: Grand Cru Threadless Bottom Bracket-107mm - Bottom Brackets - Components I do not know if there are threadless options for other BB standards, others may.

How far into the shell were the threads crossed? If it is only the first few, chasing them should restore things to fully functional as the remaining threads will still be at full strength. If someone really ham-fisted things and threaded a cup all the way while crossed, there is much less chance of saving those threads.

How many lives does a dog have? Tell us and we'll tell you if your BB will work without significant effort.


Really there is no constant answer to the OP's question. It depends on factors like how deep the cross threading went, how tight the crossed BB was, how well cut the threads were on both the BB cups and the shell, how deep the chasing threads went and a few other factors.


An experienced guy might lend more insight. But there are also alternative BB's that don't dependent on threads. Andy


In theory a crossed thread is really two sets of threads. The good ones and the crossed ones. So if one can catch the good ones your OK. But that's harder to do then write.

To keep using the frame, your choices are either to use a threadless cartridge, as suggested above, or (if English/French thread originally), ream the shell and cut Italian threads to use an Italian thread bottom bracket. If your frame was originally Italian thread, the threadless cartridge is your best option.

This is the correct answer, if it's just the first few threads that are buggered up, the BB can be repaired. But you need a BB tap, and the skill to use it to get it to be able to put the BB back together. And you would have to be very careful when you go to start the threads on the BB cups so you don't mess it up again. And I'd use loc-tite when you put it back together.
Somebody would have to really strong, and really dumb, to get a BB cup all the way in cross threaded.

Good Luck.

Who was the person doing all this cross threading on your bike....?
Put it back together with some threadlocker and forgetaboutit.

You bought someone elses problem?

How many sets of new chainrings is one set of bearings good for? Although the bearings are cross threaded in the bottom bracket, they are threaded on all the way and I might as well run a new drive train with the same bearings. They should be good for a couple of new drivetrains, right? Thanks for all the advice.

btw: This is an XT outboard bearing setup.

Crossthreading the bottom bracket all the way in once is bad enough. Having the threads chased and then cross threading it again is nearly incomprehensible.

Outboard bearings are very picky about alignment across the bottom bracket shell. With one side cross threaded, there's going to be a massive (in bearing terms) misalignment of the axle as it passes through the cups. At best, you'll have drastically reduced bearing life. Worst case, it'll feel so bad you won't even want to ride it.

For a good installation, sure, good bearings will generally outlast your interest in the bike. I wouldn't bet on that happening in this situation.

When I encouinter cross threaded parts USUALLY I can carefully work the part back in straight.Sure there is thread damage, but so far I havent had a failure on something screwed back in correctly. Give it a try. As mentioned previously, chasing the threads may render the frame useless from too much metal loss.

-SP

If you've tried everything and it's not looking good, you can try and salvage it with JB Weld. Shell has to be squeaky clean / degreased. JB Weld in combination with the old threads, then recut right through the old correct threads. Primitive Pete needs to stop with the cross-threading.

.
...how many people does it take to cross thread a lightbulb ?

Far fewer then the number to beat the subject into the ground. Andy

A good thought but with now two sets of threads in the shell it's actually easy to start the cup in the wrong set and if not noticed (and this is the aspect that would be very sad) the result is once again a crossed cup. I have seen it done. Andy