I know this is a stupid question, but how do I remove a head tube spacer? I tried once before (without advice) and thought the entire front end was going to fall apart. I got scared and replaced it. How is it really done?
undo the cap screw and the stem bolts.
remove the stem/bars
remove the spacer
put the stem/bars back
put the spacer you removed on top of the stem, or cut the steerer tube accordinly
align the stem with the wheel
tighten the bolts on the stem a little bit, just to give you some resistance so things don’t move too easily
tighten the cap screw all the way, making sure everything is still aligned
tighten the stem bolts all the way.
ride.
Remove the top Allen bolt , loosen the two stem clamp Allen’s . Slide the stem & bars off the top of the steering tube. Remove the spacer or throw it on top of the stack over stem before you clamp up . If you make a large change you may need to cut your steer tube and get a new stack up, which can be a bit of a pain without tools and a box of spacers
This is best done with the bike on the ground as the fork could fall out ,when on a stand. Be careful when adjusting the preload on the steer tube bearings , as its a fine line between too much and too little.
“tighten the cap screw all the way”
Only do this if you want to be unable to steer and ruin your headset in short-order.