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I have bought a second hand bike and generally it's going well. However, there is a small amount of play in the headset that I've been trying to diagnose and resolve.

It's a threadless fork.

I've adjusted the tension by loosening the headstem bolts and tightening the top cap. I tighten it up a lot and this reduces the play a little, but when I brake hard or hit a bump I still get the 'clonk' as it moves to the limit of it's adjustability.

I've used this article on Sheldon Brown for the terminology I use below, particularly this photo:

enter image description here

I've taken some photos and have an idea of what the problem is. In this photo I've laid out from left to right the dust ring, followed by the compression ring.

enter image description here

When the compression ring is placed on the steerer tube, there is slight gap between them. It's maybe a millimeter, although I don't have anything to measure that with here. Watching the movement carefully I'm quite confident that it's this gap that's causing the steerer tube to clonk around.

enter image description here

I've measured the steerer and it's 28.6mm which is 1 1/8" according to Sheldon's site linked above.

So why is there a space around the compression ring? What's the best way to resolve this? Do I just need to find a smaller compression ring somehow? Or is there something I'm missing?

Updated: Added text to photo


Update

I think I'm missing a part. If you look closely at the exploded graphic from Sheldon, the compression ring has a gap in it, allowing it to shrink onto the steerer tube and hold it firmly. My compression ring is solid, so nothing can shrink and grip. Kudos to Zen as well, since he mentions that it's a wedge. I'm going to have a look around at home to see if I can find the missing bits. Otherwise a new headset should sort it. Thanks all!

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You might have the wrong size headset based on your latest picture and comment. –  Ken Hiatt Feb 14 '13 at 1:53
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2 Answers 2

up vote 4 down vote accepted

The compression ring is a wedge. There will always be space and movement here, until the headset is assembled and adjusted.

It looks like you're missing a part. There should be another hoop with a wedge shape and a split. It's the split ring on the upper left in the image below. This part is what grips the steerer tube tight and will eliminate the clonking you're experiencing.

enter image description here


If you are confident that all the parts are there, and assembled in the correct order, then you have 3 likely reasons for movement:

  • The first is that there is damage to the bearing cartridges. This can show as movement when adjusted correctly, although usually on a headset it will fail first by being rough or crunchy feeling.

  • Secondly, there may be movement between the frame and the headset cup, which can mean that the frame is in need of replacement. This can't be fixed via adjustment. There are ways to attempt a fix, but it is best looked at by a qualified mechanic, first.

  • Last, there may be no movement in the headset, but you could be feeling movement in the brakes, depending on how you are checking for movement. Try checking for movement by standing the bike on the rear wheel, turning the handlebar all the way to the left or right, and checking for movement with your hand around the headset. That way if it is in the headset, you will feel it directly.

I hope that is helpful.

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Thanks for the suggestions. I've checked and from what I can see none of them apply to what's happening with me. I can see that the compression ring is a wedge and tightening the top cap will cause it to engage tightly with the bearings, which is what is happening. However nothing will cause the ring to tighten against the steerer tube and that is where the slop is occurring. –  Mac Feb 12 '13 at 22:59
    
I added some text to the second photo pointing out where I think the problem is. Does that help? –  Mac Feb 14 '13 at 1:13
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Can't tell from the picture as it's not assembled to that point, but you should also make sure you have enough of a gap for the compression to be effective. Before you put on the top cap, the steer tube should be approx 5mm below whatever spacer, seal, etc that you have as the topmost element.

If there is not enough space for complete you will get the symptom you describe (holds okay until you put sudden force to it and then it moves).

Here's the gap I'm referring to:

(via: http://www.parktool.com/blog/repair-help/threadless-headset-service)

headset gap from Park Tools web

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Thanks Ken, there's definitely enough tension. In an effort to stop this movement I tightened it so much it was difficult to turn the bars! Of course, I backed it off before I took it out again :) –  Mac Feb 12 '13 at 22:36
    
The tightening only adds compression if there is enough of a gap. From the comment you just made (and the one above under Zenbike's answer) I think you don't have enough gap. As you tighten, the top cap should NOT come in contact with the steer tube. The bolt applies the compression, if the steer tube touches, you stop adding compression. –  Ken Hiatt Feb 13 '13 at 17:07
    
I'll add a photo soon, but i'm sure there's enough of a gap to get plenty of tension. Hmmm. I'm clearly not explaining this well enough. –  Mac Feb 13 '13 at 22:08
    
Yep, I understand what you're getting at and I do have enough of a gap there. –  Mac Feb 14 '13 at 1:13
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