tuvok

I have been adjusting a few headsets recently and I have been using an incremental approach where I adjust the adjustable race and tighten the lock nut and then check for play etc. I find that sometimes when I try to loosen the lock nut to readjust the headset, the stem and handlebar get pushed out of alignment (usually because they get used for leverage or are obstructed so they cannot turn with the headset).

The end result is that while the wheel is facing one direction the handlebar and stem are facing another. At this point I loosen the stem, correct its alignment, and then continue adjusting the headset.

With regard to this issue I have a few questions:
1) Should by stem be tighter so that it does not get pushed out of alignment?

2) What are the most likely adverse results? Can you make a steerer tube unusable by grinding too much of its inside surface through this slippage?

3) What is the best way to prevent this from happening?

The funny thing is that as a kid when this happened (usually after a fall or failed stunt) we would just put the wheel between our knees and twist the handlebar till it was straight. Now that I'm older I sometimes wonder how those BMX bikes just kept on going.

Icey_rr1

Are you using suitable low profile headset wrenches?

The stem should be tight enough to not slip when making hdset adjustments on a threaded headset,
or remove the stem completely and use the fork to check for play while you make adjustments.

You should be applying a thin coat of grease to the stem before installing and no you shouldn't have to worry about the stem grinding material off the inside of the steerer tube.

tuvok

Yes on both counts (correct wrench and grease on stem). I was thinking something like removing or at least loosening the stem would be the way to go.

DannoXYZ 

To do headset adjustments correctly, you need TWO headset wrenches. One to unscrew the adjsutable cup upwards into the lock-nut. And one to tighten the lock-nut down onto the adjustable cup. If you hold the adjustable cup by hand and tighten only the lock-nut, you'll end up spinning the adjustable, and/or getting insufficient clamping pressure and the adjustable-cup will wander out of adjustment on its own later.

WNG

Technically, a headset wrench shouldn't be needed to hold the cup stationary. Since the spacer in between the cup and locknut in not suppose to rotate due to the tab resting in the fork's index.
Of course in real life, the spacer ends up twisting and turns the cup.

HillRider

The stem can be tight enough not to slip and will have no effect on headset adjustment. Even if it does slip, you can align it properly after the headset is adjusted. The two adjustments don't effect each other unless you tighten the stem expander with a 4' wrench

tellyho

Yeah, stem is independent of headset adjustment. Get the headset dialed in and then put the stem wherever you want it.