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On a new-ish CX bike (about 1 year old), I frequently need to adjust/tighten the headset bearings (semi-integrated ahead type).

After a few rides, they become loose which is noticeable by a "shuddering" feeling when using the front disk brake. Additionally, there is noticeable play in the bearings when I pull the brakes and move the bike back and forward.

What can cause the headset to become loose that quickly? What can I do about it? I already tightened all screws on the stem to spec (the label says "all max 8Nm") after tightening the adjustment screw, is there anything else I can try without specialized tools or replacing the headset?

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  • Does the fork have a carbon fiber steerer? – Argenti Apparatus Mar 22 '18 at 11:34
  • @ArgentiApparatus AFAIK, it is has carbon blades and an aluminium steerer tube. – anderas Mar 22 '18 at 14:09
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    Tightening the screws on the stem is not enough. There are videos on YouTube and on Parktools' site that show how to adjust the headset properly. youtube.com/watch?v=ZK5u5ioZU8M – Carel Mar 22 '18 at 14:10
  • If steerer is CF I would advise using carbon assembly compound which helps grip the composite. – Argenti Apparatus Mar 22 '18 at 14:12
  • If it were an old school theadded headset, I'd put low strength locktite on the upper threads to help the top cone stay still. And then I'd tighten down the locknut onto the top cone firmly. (commenting for completeness) – Criggie♦ Mar 22 '18 at 19:13
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A few months ago, I finally found the most likely reason for my problem: Instead of a star nut, this bike uses an expander plug under the top cap. This plug extends about 4mm above the end of the steerer tube, like this:

######### 
|#######|
|#######|
|#######|

Where the # represent the plug, and the | is the steerer tube. I had the stem at the topmost position, and I suspect that it not only gripped the tube, but also the compression plug. Which in turn was loosened by vibration and the stem moved upwards with it, loosening the bearings.

I have since moved a spacer above the stem so that it does not touch the plug; this seems to have fixed the problem. The lower handlebar position is fine with me, and my problem hat not re-occurred for the last months despite riding some rough-ish trails.

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  • But as others in the comments have pointed out: If the stem is clamped down with the correct torque it shouldn’t shift even if you remove the cap and nut. I think some weight weenies even do this for maximum weight savings. Insufficient space between cap and tube can be a problem but if you are able to tighten it far enough to remove play it shouldn’t have been be the culprit in your cause. – Michael Oct 29 '18 at 7:10
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    @Michael: The problem is: If the plug is slightly wider than the tube, then I wouldn't even be able to remove the plug as the stem is clamped to the plug instead of fully clamped on the tube. This is the only logical explanation for me; after moving the spacer, I still used the same torque as specified (and as before) so the torque shouldn't be the culprit. – anderas Oct 29 '18 at 7:26
  • I'll see if I still have a photo of the plug to make things more clear; otherwise, I'll add it as soon as I disassemble that part of my bike again. – anderas Oct 29 '18 at 7:29
  • Ah, yes, that could be an issue. Though the stem’s clamping area is split in the middle with a screw for each half, so at least the bottom half should still clamp to the tube, maybe to avoid precisely this issue. – Michael Oct 29 '18 at 7:32
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    All stems do not have the split clamp. Iirc it's recommend that with carbon steerers you use one spacer on top of the stem, probably this is one reason why – ojs Oct 29 '18 at 8:54
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It could potentially be a slipping starnut, similar to this: http://forums.roadbikereview.com/components-wrenching/slipping-star-nut-42741.html Albeit a less severe case since it only seems to happen whilst riding.

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    The stem should be clamped on so that it doesn't shift even if you remove the top cap – ojs Oct 29 '18 at 6:14
  • Thanks for reminding me about this question! I since have found the reason for my trouble, and will post an answer :-) – anderas Oct 29 '18 at 6:58

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