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I just replaced a fork with a different one (Bluto»Mastodon) and, after inserting the compression ring into the top bearing (it has a tapered section), the steerer tube still wiggles from side to side. The bearings are new so there's no chance they are damaged. The entire set-up worked just a few moments ago without any problems, but now I cannot seem to figure out how to get it to stop moving. What could be the problem?

Here's a photo:

enter image description here

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    I think some movement is to be expected until you create compression by tightening the top cap – Andy P Oct 9 '18 at 12:07
  • @AndyP I have a semi-integrated headset, I don't think it creates compression from the top. – Dmitri Nesteruk Oct 9 '18 at 12:09
  • As I understand it (and i may be wrong), the compression ring needs compression from the top to work. It is forced down so the tapered area goes deeper - it is already flush against the bearing, so the only thing that can happen is for the 'gap' to close and become tight around the steerer. – Andy P Oct 9 '18 at 12:15
  • Do you mean it wiggles before you've reassembled the whole thing, or afterwards, when the top cap has been tightened/adjusted? – Swifty Oct 10 '18 at 18:47
  • @Swifty it wiggles after everything is tightened – Dmitri Nesteruk Oct 10 '18 at 20:59
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There's often a very thin intermediary washer/spacer piece that goes between the compression ring and the top plate. Some headsets have it and some don't, but on one that was intended to have it, leaving it out would cause the exact problem you're talking about, as the top plate would bottom out on the bearing cup or headtube before it makes contact with the compression ring.

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  • I did not have such a space on the other fork. – Dmitri Nesteruk Oct 10 '18 at 20:58
  • The only other thing I could think of would be some weird tolerance problem where the slit in the compression ring was bottoming out on itself without letting the ring do its job. Or in other words if the slit wasn't wide enough. You could corroborate that by pushing down on it directly with some spacers with the top plate off. If this is what's going on you could just take off a little bit of it with a file or angle cutter etc. – Nathan Knutson Oct 10 '18 at 23:17
  • Couple checks I'd add would be is the starnut in such a position that the threads of top cap/ bolt assembly aren't bottoming out at the nut before the cap/bolt assembly have exerted proper bearing compression. (I'm picturing a bolt design with a long collar followed by threaded finish. Not all thread IOW.) Related to that, the top cap should be tightened for bearing compression with the stem bolts loose--no more than barely snug. – Jeff Oct 17 '18 at 8:16
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Judging from the photo, it looks like the split ring (which I think you are referring to as the compression ring) is installed upside down. If flipped over so the the thinner part of is at the bottom, then it should fit between the steerer tube and the inner surface of the bearing.

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  • hmm, interesting. it looked the right way to me, but now I can't tell from the photo which way up it is. giving +1 for benefit of the doubt, good spot if correct! – Swifty Oct 10 '18 at 18:49
  • No, the ring is the right way around. – Dmitri Nesteruk Oct 10 '18 at 20:57
  • Ok. I wonder then if it is a problem at the lower bearing. Did you fit a new crown race to the new fork? If that's missing or not seated properly it could cause this. – clubdog Oct 10 '18 at 22:35

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