5

I removed my bottom bracket because there was creaking sound while I was pedaling. Cleaned it and wanted to reinstall but the crank in the middle was hardly turning when I fully tightened the cups on both end. Removed it again saw it wasn't centering the shell. Why do you think this would happen and what should I do to correct it?

enter image description here

3
  • 1
    ...that definitely would be a cause for creaking....
    – Criggie
    Feb 7 at 6:46
  • Can you look upward or downward at the cup on the other side of the frame? ou're looking to see if its parallel with the face and at right angles to the centerline of the BB. If you back out the drive side by half-a-turn, does the axle perk up and change angle or does it stay about the same? If the former, something's bent and if the latter, it sounds more like cross-threadded.
    – Criggie
    Feb 7 at 11:28
  • OP, note that I edited the title for clarity. Feel free to undo the edit if it doesn't reflect your meaning.
    – Weiwen Ng
    Feb 12 at 20:37

3 Answers 3

4

It's cross threaded and the frame threads are likely the worse for it.

From the position you're in, the chance of ruining the frame is likely minimized if you get the threads chased before doing anything else.

If you just go straight to trying to get the BB installed in the correct, original set of threads, it can be dicey to know when to apply the force needed to get it back on track so it doesn't go back in the wrong way, which it will want to do now. It will likely also take force the whole way. It's not necessarily impossible to go this route and have it work out, but it may take finesse. Meanwhile, BB taps are built to be good at clearing this kind of thing up and give you a lot of assistance in staying on center. If the NDS threads are still good, using that side as the reference for the pilot pretty much does the job by itself.

In a low-resource situation, a suitable chasing tap can be made from an old fixed cup, especially since the frame is al.

2
  • I'll consider to buy a tapping tool. Thanks.
    – Ender
    Feb 13 at 13:30
  • @Ender They're expensive so it's typically a shop-level thing. However, bringing a shop a bare frame to get the threads chased is usually not a very expensive service. Feb 13 at 15:15
4

You have probably cross threaded the bottom bracket (BB) (inserted and tightened at an angle) when installing it, and your shell's threads might have been ruined.

One should inspect the BB from the non-drive side (NDS) side when inserting the BB to make sure the BB is in fact centered and not angled before tightening. The initial insertion should also be done by hand to prevent excessive force being used in case you have cross-threaded/not cleaned the threads properly. I usually insert the NDS cup somewhat as well before tightening the drive side (DS) to confirm alignment and have the NDS cup act as a guide.

Overtightening the DS/NDS will prevent the spindle from moving freely, even if you have correct alignment.

You could try to remove it and reinsert it correctly, but the threads are probably damaged and the risk is that you will not be able to insert it correctly and only make things even worse. Or perhaps the soft aluminum is forgiving and it can be saved (if the threads on the BB and not the shell caved) I'm not sure what the best option is as I have never done this. It might be beyond repair.

9
  • I should buy a brand new BB and see if it will be centered or not. Maybe something wrong with the BB because the bearing on DS has been replaced today by our local bike shop. They used some non professional tools to do that.
    – Ender
    Feb 6 at 19:25
  • @Ender The risk here is that the threads in the BB-shell might be damaged. But if the threads on the BB-unit was what gave in then a new BB might work. I thought this was a cartridge BB-unit?? Good luck anyway!
    – WornChain
    Feb 6 at 19:31
  • Yes cartridge type.
    – Ender
    Feb 6 at 19:32
  • 2
    If the threads in the bottom bracket (BB) shell are indeed cross threaded, a trip to a well-equipped local bike shop (LBS) may be able to save the threads if rethreading in the BB straight cannot be achieved. The well-equipped LBS may have a BB shell thread tap/thread chaser, and it may be able to salvage a cross threaded BB shell. Don't make things overly worse if it cannot be straightened out without the tool to salvage what you can before too much damage is done. These are pricey tools that are not used too often, but when needed, they can be a BB shell saver.
    – Ted Hohl
    Feb 7 at 5:44
  • 1
    @Ender I'm no expert in this area but I doubt that is the cause. If the 68mm BB fits (diameter and thread type) being too short should not cause this kind of misalignment by itself. For instance Shimano seems to use the same threading on their BBUN300s regardless of axle width. However, if someone at some point inserted a BB with a different thread type than the shell was made for, then perhaps issues like this would occur. But as stated, I have no experience with this problem, I'm just reasoning from what I'm seeing.
    – WornChain
    Feb 7 at 10:42
2

Indeed looks like it was cross-threaded at install.

I was once able to save a lightly cross-threaded bottom bracket thread using a makeshift thread chaser. I took an old bottom bracket cartridge, pulled the shells off, and used a Dremel tool to make little ridges in the shells (kind of making it look and function like an actual tap). With some cutting liquid and a metal brush, that was enough and I still ride that bike many thousands of kilometers later.

If the threads are very badly cross-threaded, even a thread tap might not fix the problem as the shell will be loose in the thread.

One possibility could be using lots of hard threadlocker instead of grease/antiseize.

As a more radical solution, I have seen (can't remember where) hybrid cartridge bottom brackets for trashed thread. They have BSA thread as well as internal thread that pulls the left and right cups together (the same way as on some press-fit systems).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.