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Just like one or two months ago, I had noise coming from bottom bracket and my LBS changed it under warranty. But after few rides (not exactly remember how many) I had a little movement on BB. It makes a click move but w/o noise. Investigated and saw that entire BB was moving inside the shell. I brought it to shop and they tightend it and problem solved for a little while. Now it is there again but less, and I am worried about threads are stripped. Bike is still like 17 months old and it's under warranty. Anything else could be but stripped threads? Thanks.

Edit: I brought my bike to LBS and try explain the situation. The shop owner and mechanic had a ride and they saw nothing problematic. I gave a little bit more explanation to them and show how I can feel it. I am not sure they did but shop owner said there is a millimetric play but again I can't tell if he felt or trying to convince me. They remove BB, greased again and reassembled. In process, I noticed when mechanic inserting left side cup he had a little bit hard time correctly, It looked like not want to go in. After he put correctly, turning it was easy. He didn't use tork wrench but he used a pistol like they use in Formula1 pit stops. I don't know well if it is torque density but I hope they tighten it correctly. No problems for now. Thanks everyone for their help. I hope it won't occur again. Sorry if my grammar bad.

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    By entire BB moving inside the shell, do you mean it had come loose and was turning on its threads? It's hard to understand what's going on here without knowing the bike, cranks, and BB in question. Jan 30 at 16:34
  • I mean it move on vertical axis like upwards and downwards. I can only see non-drive side because of crankset and movement is so little not even a millimetre but can feel it when I push one pedal to downwards It makes a click move and that is it for same pedal. It stops making until this after I push the other pedal same. Push left, click; push right, click. My bike is a local bike from Turkey, Bisan TRX 8400. Crankset is SHIMANO FC-M371-L and BB is SHIMANO BB-UN300. Alu frame. Jan 30 at 17:36
  • In reply to the edits, sounds fine. Having to struggle a little to get a BB cup started is fairly common. Using an air impact driver is fine; what I don't like about that is it takes away your ability to feel whats happening, which can sometimes reveal problems, but it certainly delivers enough torque. Jan 31 at 17:31
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    Thank you for your help, I really appreciate it. Surprisingly I was very disappointed when my LBS didn't get the problem, they are doing this job like 50 years and very famous around here. I tested it a little, still no problems but it was similar when they tighten it a month ago. I hope reassemble process solve the problem and I won't mess with them anymore. Feb 1 at 13:05

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You or a shop need to pull the BB out completely to assess what's happening.

Best case scenario is it was initially assembled dry, no grease on the threads, and their efforts to simply tighten it before didn't work because no lubrication meant insufficient thread preload was achieved. If that's true then greasing the threads and reinstalling the BB will likely fix it.

Worst case is the threads are toast. Aluminum bikes do not have great tolerance for being ridden with loose cups, and the threads getting destroyed can result. Root causes could be poor thread quality, poor prep/lubrication, and/or poor installation torque.

If you can literally see the bottom bracket cups moving up and down in the frame, either the cup or the frame is probably toast, and I believe BB-UN300 has a steel drive-side cup so it's probably not that.

Threadless repair BB cartridges exist to be a fix for the above, but have their own problems and aren't an acceptable solution for a new-ish bike still under warranty.

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Sounds like your frame's Bottom Bracket housing isn't supporting and retaining the BB cartridge.

For an old bike I'd probably clean out the threads on both sides of the BB housing, and inspect for cross threading and chips/slag in the threads.
If I had the thread chasing die, I'd run that in and out both sides as a cleanup - your bike shop should have this tool.
Then I'd fit a new BB cartridge like the BB300 you have, but use a low-strength thread retaining compound like blue locktite; specifically the hand-tool level, not the red sorts that need heat to release.

Downside, the next guy is going to hate you when it comes to changing the BB (and the next guy is likely to be you :)

I think your BB housing threads in the frame are a little oversized, and your BB endcaps are not getting a good grip. Overtightening probably won't help.

It is also possible the ends are bottoming out somewhere and you're not getting full torque on the lands of the threads.

Grease/assembly lube shouldn't affect this, make sure you have some but not excessive amounts.

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