Hey guys, I'm working on a bike (threaded headset) where I'm swapping out the stem. Yesterday, the stem was loose enough that I could easily rotate it independently of the fork, and remove it with some wiggling. I tightened it, and then today, when I went to loosen it and remove it, the stem is totally, irremovably stuck. If I loosen the stem bolt, it just rises; taps with a mallet don't budge it. If I remove the stem bolt completely, the stem still doesn't budge. How could this possibly happen overnight? I'm up for trying to put oil, ammonia, in it, etc, but it seems like it must be another problem, because it's not like the stem corroded in place overnight. Any ideas? Thanks,

-Colin

Sounds like you have one of those steerer tubes that has a narrower section further down, and now you've gotten the wedge and the stem jammed up against this restriction. Don't know if Sheldon Brown has a patented cure for that on his website or not.

If it was me I'd undo the bolt and then hit the stem from below (use a wooden block in between) to try to dislodge it.

I had to use a torch to get a seat post out the other day!!

Just loosen the stem polt (don't remove it), and then slightly knock it (stem polt) with hammer. Wedge/expander should come loose instantly.

But if you should really have some kind of steerer tube that's narrower further down, that I have never seen, then try removing stem polt and then try pulling handlebars out, twist and use some force if necessary. If you get it out, then screw stem polt back into wedge/expander and do circular moves with head of the stem polt to get expander loose.

Or use the method described in previous post

Is your stem jammed down low? If so, dabac may be right about jamming with the internally butted steerer. His wooden block stategy sounds right.
From Sheldon:

Stem not down low?
Whether the stem has a wedge or a conical jammer, either can set up weirdly when tightened.
How hard are those taps you're giving the stem bolt? Persuasive?
Maybe a proper hammer with a bit of wood over the bolt head to protect it.

Start by loosening the bolt then tapping the stem down in the normal way. Next remove the bolt entirely, and try twisting and lifting the stem at the same time, If the bolt is wedged against the internal swage it might resist, so set a wooden block against the bottom of where the extension meets the quill and give it a sharp upward rap with a hammer. That should pop the stem free, and you can retrieve the expander later with the bolt, or by removing the wheel and pushing it out from the bottom.

+3 Inserted too far. Push it up from the bottom.

Thanks for the tips guys. Hitting upwards with a hammer, with wood between stem and hammer, didn't help, unfortunately. On the one hand it doesn't make sense that the stem is down too far because based on the length of the bolt, it looks to be about 1/2 way down the steer tube. On the other hand, I do remember that the stem was not willing to go down much further than where I tightened it, so perhaps the steer tube starts to taper early? The fork is a Time Stiletto, carbon, so I have not been really brutal when it comes to trying to twist it out (though I have certainly tried to twist it out), and I have no idea if it's a tapered steer tube or not. I have been giving it persuasive taps, both with a mallet and hammer with wood, but not really really hard taps, don't want to mess anything up internally. Is there any sort of jig for me to get better leverage when trying to push the stem out from below?

-Colin

You can try loosening the bolt a few turns. Holding the stem, lift the front end of the bike off the ground and have someone rap the top of the bolt with a mallet (use a block of wood to keep it pretty).

Sorry, i advised you to try to skate by using a shortcut earlier.

The secret to effective hammering is an anvil or a dolly ( a sort of hand held mini-anvil) to add to the inertia of the hammered part and concentrate the force. If you have a bench vise, open the jaws to just clear the stem and have a friend hold the bike upside down with the headset laying across the jaws. Then drive the stem down (after loosening it -doh!") using a wood block set against the base of the extension. With the headset and fork immobile the stem will move. Once it's popped free, slowly work ir loose.

Note overly working jammed aluminum parts can heat them to where they're softer and cause gaulling which jams them tighter yet. That might be what happened earlier. Adding penetrating, or cutting oil helps prevent them from seizing.