micro millimeter steerer tube diameter differences and its effect on headsets.

[Rushdee]

So I have a Chris King headset (hereafter referred to as CK). My Fox Float CTD 29” Kashima 140mm fork (hereafter referred to as Float) was sent away for some maintenance and I fitted a RockShox Revelation 29” 140mm (hereafter referred to as Rev) as a temporary fork. Turns out that the steerer tube diameter of the Rev is a nano millimeter narrower than the steerer tube diameter of the Float. Whatever happened to industry standards I say? Nonetheless, the result is that there is chafing/rubbing of two parts in the upper headset assembly. See red arrow in pics, and pics of my actual headset showing the wear/damage - you can see the CK branding disappearing due to the wear. Not really sure how a narrower steerer diameter causes this but when I turn the bars all the way to the right I can actually feel the slight resistance caused by the chafing. When the bars are turned all the way to the left the resistance is still present but slightly less. During assembly and with the stem bolts loose I ensure that I dont damage the headset by over-tightening the top cap bolt - I ensure that I apply just enough torque to pull the headset into place and so that there is no play/movement in the headset (torque wrench not really necessary here - it's more about feel, applying front brake, rocking bike back and forth/side to side while tightening etc), then I tighten the stem bolts - as per many YouTube guides. Bear in mind, I apply the same assembly method with the Float and the chafing is absent. Chafing only occurs with the Rev. Hence my suspicion of the steerer diameter being the cause. Also, immediately after assembly I go for a ride and the chafing and resistance is light and minimal but as soon as I ride any rough stuff the chafing and resistance increases and then remains constant. Any thoughts welcome. Google not really helping much. Although the wear is minimal, it's kind of not cool to see this kind of wear on a headset, especially on a pricey CK headset   

 

[Pulse]

Sorry Eric, don't really know what you are asking...

 

Your theory seems plausible

[Butterbean]

I don't see how it would cause that. There is that split piece which compresses into the space so would compensate, especially for minute differences.

 

I suspect you might be missing one of those super thin metallic spacers, as without them, the compression happens, but likely is leaving too much or too little space between the parts being worn down, and then giving it the opportunity to rub.

 

Hope you come right tho man

[David Marshall]

I agree with DragoRosso.  You might also check that the top cap is totally clear of the steerer tube, even if you have to preload the bearing with an extra spacer above the stem.  You can remove it when the stem is tight.

[Rushdee]

hmmm. Weird thing is that the chafing doesn't occur with the Fox Float (meaning that assembly is correct & that a spacer is not needed & that top cap is clear of steerer tube -> on both forks). The chafing only occurs with the Rev fork and the only noticeable difference between the two forks is steerer diameter. Rev steerer is a fraction of a millimeter narrower than Float. Don't understand how steerer tube diameter could cause the chafing though? Unless something else is the culprit. I've highlighted the steerer diameter as a possible cause but I could be wrong (especially since I don't fully understand how it impacts the top assembly). Thoughts? 

[JXV]

hmmm. Weird thing is that the chafing doesn't occur with the Fox Float (meaning that assembly is correct & that a spacer is not needed & that top cap is clear of steerer tube -> on both forks). The chafing only occurs with the Rev fork and the only noticeable difference between the two forks is steerer diameter. Rev steerer is a fraction of a millimeter narrower than Float. Don't understand how steerer tube diameter could cause the chafing though? Unless something else is the culprit. I've highlighted the steerer diameter as a possible cause but I could be wrong (especially since I don't fully understand how it impacts the top assembly). Thoughts?

If the Rev steerer is slightly smaller diameter the collet (cone shaped bit) will sit a bit deeper in the top race and likely reduces clearance between the fixed cup and the rotating top collar. Try a thicker O-ring to start otherwise a spacer shim will be needed.

 

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[Wolf Lyle]

If the Rev steerer is slightly smaller diameter the collet (cone shaped bit) will sit a bit deeper in the top race and likely reduces clearance between the fixed cup and the rotating top collar. Try a thicker O-ring to start otherwise a spacer shim will be needed.

 

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that sounds like the answer to me. applying a thin spacer would then compensate for that !

[JXV]

that sounds like the answer to me. applying a thin spacer would then compensate for that !

Could also 'thicken' the steerer with a strip of thin shimstock inserted between collet and steerer. This will make the collet sit higher....but fiddly to get it right.

 

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[JA-Q001]

Just an observation. As you can see, the wear / contact is only on the left side. If there was play, the wear would be on the back, as the angle of the fork forces the weight to that side.

 

The culprit here would rather be the headset inset not being installed correctly, in was not pressed in flush with the frame.

 

A thin spacer can solve the contact, but bearing life is compromised due to the concentricity of the top and bottom bearing being off.

[JXV]

Agree with JA-Q001 that the one-sided wear pattern shows the top cup is apparently misaligned. If both cups are fully pressed in then maybe the head tube itself is slightly off - top and bottom faces not parallel.....or the top bearing not properly seated.

 

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[Rushdee]

Thanks for the input gents. I agree that with a narrower steerer the cone shaped bit (assuming that you are referring to the split ring indicated by the red arrow in the pic below?) will sit a bit deeper and likely reduce clearance between the fixed cup and the rotating top collar (clearance indicated by the two red arrows in the other pic below).Going to try a thin spacer or thicker o ring as suggested and post my findings as soon as family life allows.

 

[usxorf]

Just a shot in the dark here, eric. Did you swap the crown race between the two forks? Not sure if it should make a difference but to rule it out.

 

Otherwise digital calipers the steerer tube diameters.

[Skinnyone]

Unfortunately, the fork steerers will never be the same diameter even within the same manufacturer, manufacturing tolerances etc. Never mind that they have to account for the multitude of headsets on the market and their tolerances as well. Hence that split ring to make up the differences in tube sizes as well as bearing sizes.

 

I think a micrometer difference is acceptable, 1 mm difference and you got a whole new set of problems. 

 

It is a small sacrifice to fit a shim under the top cap and make do for now. 

[Rushdee]

Just a shot in the dark here, eric. Did you swap the crown race between the two forks? Not sure if it should make a difference but to rule it out.

 

Otherwise digital calipers the steerer tube diameters.

Crown race swapped between two forks yes. CK recommends that a CK specific crown race is used and I followed this recommendation.

[Spoke101]

JXV hit the nail on the head. Just place a very thin shim on top of the split ring and the problem should be sorted. If not there are bigger issues at play.

[droo]

100 ZAR says your head tube wasn't reamed and faced before the headset was installed, hence the misalignment.

 

I know this because there are about 2 complete facing sets in the whole of Cape Town.