Monkey D.Luffy

Hi all. I've been flipping the stem on my bike to try another lower angel for the stem. After taking the stem off of the bike and turning it upside down and putting it back, sometimes the spacers are a little loose and the fork/ front wheel seems to wobble it bit, even if I press down on the stem a little to secure it back into place. Is there any reason for this? I'm not removing or changing any spacers.

JanMM

Have you checked/adjusted the star nut for correct tension before tightening the stem in place?

FBinNY 

Something changed.

Either you dropped and lost a spacer, or the star nut slipped upward and the screw is running out of thread, or something else with the similar effect of preventing you from properly setting the preload on the headset.

SkyDog75

Like JanMM suggested, it sounds like you're not setting the stem preload before tightening the stem into place. With the stem bolts loose, you need to use the bolt running through the top cap to adjust the headset and remove play. Once you've tightened the top cap down just enough to remove all play from the headset, then tighten the stem bolts to secure it to the fork's steerer tube.

For more detail, you can check out the tutorial on threadless headset service on Park Tool's blog.

Andrew R Stewart 

Agreed, the headset bearing preload must be set after each time the stem is played with. Most threadless designs require this to be done by tightening the steerer cap draw bolt until there is no slop in the headset bearings before the stem clamp bolts are secured tight. One very good method to ascertain the headset bearing setting is to use the front brake to lock the front wheel and then rock the bike back and forth when grabbing the handlebars and brake lever. if there's any slop in the bearings the fork and bars will knock/rock a bit within the headset and frame. One should be able to feel this. I work from having the bearing pre load a bit loose, better to feel which side of the fence you're on. Then bit by bit tighten the cap draw bolt up tighter and retest. Again, if you feel no rocking/slop then loosen the draw bolt till you can. It's real easy to have too much preload and not know it. One trick I use is when there's still a slight rock in the fork/frame/bearings I'll tighten the stem clamp bolts and retest. Sometimes the loose stem (on the steerer) can add "noise" to the rocking test. For an experienced wrench this process takes only a few minutes. for others it might be a bit more and might also need to start from a known looseness a second or third time to fully learn what to feel for. the "perfect' headset bearing preload is when the rocking/slop is just barely gone and the stem is tightly clamped pointing straight ahead. Andy

Monkey D.Luffy

I see. I was trying to tighten the stem bolts first, then the top cap nut, but that resulted in play 1 out of 2 times.

If I am understanding correctly, would the correct method just to be putting the stem back on (without tightening the stem bolts), then tightening the top bolt to remove play, then secure the stem?

FBinNY 

Yes, basically. Once the stem clamp bolts are tight, you've locked in whatever the adjustment is.

Monkey D.Luffy

Much love to the informative replies. I've been tightening the stem then the top cap in the wrong order before. Oops.

Thank you all for the info, it fixed the issue almost immediately.

dsbrantjr

The only function of the top bolt and cap are to set the bearing adjustment. Once the adjustment is locked in by the clamp bolts, the top bolt and cap serve no purpose other than hole-filling. They can be replaced by, among other things, GPS mounts or water bottle holders.