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After I did an overhaul of my threaded headset, it loosens after every ride. I'm struggling to find what causes this, as I've done this job on different bikes without any problems. So far I've done the following:

  • Changed the upper loose ball bearings with a cage as the balls were difficult to keep in place. I've checked that the cage is in the right position.
  • Checked that the lock nut is not pressing against the fork tube; this wasn't the case.

What else could cause this behavior? See below a picture of the headset in question:

concorde headset

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  • Other things might be to make sure lower bearing area is properly seated and upper bearing nuts are torqued to correct range. Was there some issue that prompted the rebuild?
    – Armand
    May 9, 2023 at 2:03
  • @Armand I cannot remember exactly as it's been 2 years sinces I've done it (haven't much driven with the bike since). I think it there was always some play in the fork, even when I tightened the lock-nut up to the point that I could barely turn the handlebar. There were some ball bearings measing when I opened (maybe a fault from my side) so I decided to give it a complete overhaull but now it results in the lock-nut becomming loose.
    – wouter205
    May 11, 2023 at 10:07

1 Answer 1

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You may have stripped/damaged a thread.

You need to disassemble - slack off the quill stem bolt and pull the bars up and out. Then remove the top nut, any washers and the top cone nut.

Then clean the threads both inside and out, dry, and have a close inspection.

When I had this same situation, the underlying cause was worn/damaged threads inside the top lock-nut. It would sinch/cinch down well enough with suitable tools, but a day's riding was enough to back off the whole stack by a turn or so. Fortunately the other threads were fine.

There was no repair that felt safe, so I swiped a top locknut from a donor fork and the bike's been rock solid since.

I also took the opportunity to clean the bearings in the top and bottom (weight-bearing) race, lube and reassemble. I also put a suitably sized piece of heatshrink on the quill stem such that it covered both headset nuts, to help divert water because the rubber seals were showing age and not sealing, which may have contributed.

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  • Thanks for the suggestion, I'll give it a shot this weekend!
    – wouter205
    May 11, 2023 at 10:03

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