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This is on my mountain bike.

After returning from a ride a month or two ago, I noticed my threadless headset had developed some play. Ever since then, I've had to retighten it occasionally, maybe every three weeks or so? When it loosened again yesterday, I decided to disassemble and clean up the whole thing. I have a tapered zero stack (ZS) headset, where recessed cups are pressed into the frame and then cartridge bearings are slid in (it's supposed to be a slip fit, not an interference fit). As expected, the lower headset bearing fell right out. However, the upper bearing was firmly stuck; I ended up having to use penetrating fluid, heat, and a hammer to get it out. When I went to reassemble, the same thing happened: lower bearing slipped right in, while the upper bearing refused to enter the cup by itself. I ended up having to crank down the top cap hard in order to forcefully press fit the bearing in.

Prior to this, my headset had come apart properly every time.

  • I'm guessing my inability to get a good preload was due to the bearing not being free to move around.
  • What do you think caused this? How shall I fix it? My thought is to install a new upper cup.
  • Could my headtube be damaged? A new frame is going to be expensive!
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  • How hard is the bike ridden - been in an big accidents?
    – mattnz
    Jul 28 '20 at 19:59
  • @mattnz I live in Vancouver, Canada, so our local trails are pretty gnarly. I’m usually riding black trails but skipping all the big jumps and drops. No major crashes, just the usual bails and fails.
    – MaplePanda
    Jul 28 '20 at 21:36
  • What is the possibility the headset has been tight since installed?
    – mattnz
    Jul 29 '20 at 0:01
  • @mattnz It’s definitely never been blatantly loose, but I’m usually pretty conservative when it comes to preloading anything. I think I will try to tighten headsets harder from now on.
    – MaplePanda
    Jul 29 '20 at 6:04
  • Might the upper bearing or cup be out of round? Have you tried installing a new top bearing? Might there be corrosion in the upper cup/bearing?
    – Armand
    Jul 29 '20 at 9:17

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