play in threadless headset

[ElyDave]

All I've done is change the stem back to the original to fit new handlebars and the headset has developed fore and aft play that was not there before.

Nothing else has changed, same spacers, I have one spare but that's the same size as installed. 

Any ideas?  It's only out by a fraction of a mm

[robgul]

Preload? - is there a star nut or a "bung" in the steerer tube? ... if the latter it may not be gripping the steerer tube and holding the preload. 

[Just for clarity : the top cap and bolt are tightened down onto the steerer tube to set the preload  (i.e. the forks/steerer at the correct tension) before tightening the stem bolts that clamp it to the steerer]

I am assuming when you say "play" you mean that when you hold the bars with the front brake on the steerer is rocking backwards and forwards.

.. and I hope you used a torque wrench to tighten the stem bolts ....

Rob

Edit :  This might be useful  http://road.cc/content/feature/167572-how-adjust-your-threadless-headset

[ElyDave]

cheers Rob,

yes - star nut

yes - torque wrench

yes - play as described

All Al in this case by the way, carbon forks, but Al steerer

[yoav]

Could it be the clamp on the new stem is slightly shorter and hence no matter how much you tighten the top cap, it wont press down on the stem? For reference, you need the combined height of the stem clamp and spacers to exceed the steerer tube by about 3mm before you screw down the top cap.

[ElyDave]

that's the odd bit, this is not the new stem, this is the old stem replaced.

as far as I can tell its the same height as the new stem it's replacing.  I have a spare 5mm spacer, which would give about 4mm excess. 

Good point though, I think it's worth looking at the gap and spacer combinations

[Torslanda]

If a 5mm spacer would give you the stem at 4mm above the steerer then NOT fitting means you can never compress the bearings. You can tighten the top cap as much as you like but it will bottom out on the steerer.

[ElyDave]

4mm excess of spacer, not 4mm excss of steerer.

There is a smidge of steerer visible perhaps

[jsabine]

Yes, that's what Tors means. You must have more height of spacer+stem than of steerer.

This allows the top cap - pulled down by the bolt into the star nut - to bear down on the spacer/stem stack, and thence onto the bearings to preload them.

[ElyDave]

I was wondering if i was missing something that simple, having built up other bikes with no issues.  I have no recollection of removing a spacer though.  I'll add the spare one back in and hopefully that works

[Gattopardo]

Is the centring sleeve still there in the proper place?

[rogerzilla]

Spacers cost next to nothing and come in all sorts of thicknesses, so you can go and buy one that only just sits above the end of the steerer.  I wouldn't want a tall spacer that didn't have the steerer very far inside it  - it might not end up properly parallel to the head tube.

[ElyDave]

but that's the bizarre thing here, I don't recall changing any spacers and never cut the steerer, so the spacer that I put back on, to cure the problem MUST have been there originally.

IICBA I'll pop into the LBS and get a 2.5mm one as well.

[Paul H]

It's easy enough to check, once the bars are tightened the top cap can be removed, either the steerer is below the spacers/stem or it isn't.
Another possibility is the star nut isn't gripping, shouldn't be hard to check.

[ElyDave]

The problem is solved, it's been solved for the last 5 posts