I changed my stem yesterday, seemed to be a pretty painless exercise. Took it for a spin and noticed a bit of juddering from the front under braking but didn’t think too hard about it.

Today I had another look and there seems to be play in the headset. I’ve got a couple of spacers under the stem and they’re loose enough that I can easily spin them around with just my fingers even though I’ve tried refitting the stem with it pushed down snugly, and if I hold the front brake on and rock the bike back and forth there’s definite play and a knocking sound.

Is this coincidental or have I somehow disturbed the headset?

One thought – am I right in thinking the top cap serves no purpose other than to keep muck out of the hole? On that basis I was fitting it last, but perhaps I should do it with the stem loose so that it snugs it down?

Tighten top cap to preload bearings (but not too tight or they will bind up) then tighten stem bolts. That is why you have play.

As above you must tighten top first

If the new stem is not as tall as the old one (height of section clamping the steerer) you may also need an extra spacer, but otherwise sounds like not tightening top cap bolt first to preload bearings.

With the stem clamp bolts loose, you must tighten the top cap until the play is removed from the headset. That is what the top cap/bolt is for. Once the play is gone, tighten up the clamp bolts. You can then remove the top cap/bolt as it serves no real purpose other than to look pretty. (Nobody does though, just in case you need to tighten your headset out on as ride) The top cap/bolt is basically a tool, not a component, as such. 🙂

Although, if your new stem has a lower stack height, it may not be possible to tighten the bearings down correctly and you may need to add another spacer

He makes a bit of a meal of it, but like this:

[video]http://www.youtube.com/watch?v=RRFqU07u8DE[/video]

Thanks all, I’ll give it a go.

Works a treat, almost as if it’s designed like that. 😀

Thanks again.