I have a stem that doesn't want to leave its home of many many years. I tried shooting lube in there and twisting the bars until I got the funny vein thing going in my neck, and they didn't budge. I have since had to amputated the stem from the fork so I can work on it without damaging the frame. Is there something I could soak the steer tube in (or plug the end and fill it) that might loosen the grip of rust? I don't want to ruin the threads, which are in good condition.

PB blaster is some really good stuff to start with. After that I'm sure someone here will have some good hints.

pb blaster, coco cola, tap the stem to vibrate it a bit.

Had you left the stem intact, you could do as Southerland's recommends, clamp the fork crown in a vise, and pull and twist on the handlebars for 15 minutes at a time, let cool, start over.

What kind of stem is it? Wedge or cone?

Once I had to stoop to taking the conical wedge out of a Modolo stem, take a piece of copper pipe and beat it from the bottom of the fork till it broke loose. Use a pipe slightly smaller than the inside diameter of the stem, so you don't expand it with the pounding. I did this because a not to be named bike shop told me that the frame was trashed, and the reason one brings a bike to a shop is to have it properly serviced. Of course the punk kid had never even seen a quill stem and hadn't a clue. He did sufficiently raise my ire enough to enable me to pound it out with reckless abandon.

It worked fine, no damage done to the frame or stem. The copper pipe is useless, though.

PB Blaster is good stuff. Turn frame/fork, upside down. Spray enough in to run through (but don't waste...). Let set for a couple of days. Flip back over, use soft rubber mallet, covering what is left of the stem, to carefully drive stem DOWN, which should loosen stem, over where the PB Blaster was. If this does not work, repeat.

This is not different than a stuck seatpost, to me. Patience! You will get it!

cudak888 once told me after I had tossed the fork, that soaking the steering tube in a bucket of ______ for several days would disolve the alloy stem, leaving behind only the fork. Now I don't remember what ______ was. I think lye, but you should PM him. I hope he wasn't pulling my leg.

I have a fork that had a stem break off inside. I swear the bottom half of thestem is welded inside.
Wonder what if dissolving the stem would make it workable. Not a good enough fork to really
answer that question.

As far as dissolving the aluminum goes, you can use any strong base. Lye as mentioned or ammonia to remove the white powdery oxidization which is what usually makes it stuck. I used PB blaster and it worked, but my next plan was ammonia. Keep in mind that if the frame is Aluminum PB blaster won't do as much. Oven cleaner also works to remove oxidization from aluminum as long as it has sodium hydroxide in it. This will pit if left on longer then 20 minutes or so.

Ammonia is the only thing I have had success with but on each occasion it has ment a couple of days of working the stem backward and forward to release it.

Thanks for all the suggestions. I have ammonia in the garage now, so I think that's where I will start. The fork is Reynolds 531. so I don't want to trash it. I update if (when) I get it out. Thanks again.

We all know the frustration. I just spent the last week trying to free up this stem. The photo shows the incredients. Liquid Wrench and a hammer with a rubber and plastic head so as not to mar the stem finish.

I poured Liquid Wrench in from above and below for two days. On the second day, brown liquid started to ooze out from below showing that it was probably rust and not aluminum oxide being the primary culprit. The the third day, I put a mark on the stem where it joined the head tube with a Sharpie, turned the bike upside down and started whacking the stem at the bend but not too hard.

The first ten whacks seemed to cause a almost imperceptible movement but it was movement. I did come out with no damage to any parts. The photo shows the rust.

You May Want To Remove Your Headset,if You Cut The Stem Off. Take Out Your Fork,put The Fork And Disected Stem In A Quality Vise. Soak The Fork Upsidedown From The Inside With Liquid Wrench Then Apply A Propane Torch Carefully To The Center Of The Fork Head .and Drive Out The Stem With Along Punch.remember To Pad The Fork Collar As Not To Mar The Paint.

I just went throught this with the Ironman I purchased. We did the following: The quill broke loose almost immediatly so that's not an issue. The LBS soaked in PB blaster for several days. Upon trying to remove the stem by turning with bike in a vise, the stem broke off at the head. LBS drilled out the stem as much as safely possible to relieve pressure. I soaked it for one day in Cola, then one day in ammonia. The ammonia had a visible affect on the alloy stem changing the color to a flat gray color. Next I took the fork with the stem in it to a metal shop. They cut a wedge in the stem with a metal chisel to relieve the pressure. Then heat was applied to the fork steerer BELOW the threads, NOT on the threads. With the fork in a vise, and the stem in a vise grip, one guy (me) holding down the steel table holding the vise, another man turned the vise grip and the stem budged. ONLY AFTER THE STEM MOVED considerably did we stop trying to remove the stem from the top and used a punch to drive the stem from the steerer. Using a punch to drive the stem from the bottom is risky because the quill wedge could simply jam the stem making it even more difficult to remove. In fact, when the stem started moving the quill jammed once on us and we had to use the quill bolt to tap it loose. Then we finished the job pulling the remainder of the stem from the steerer with vise grips.
The remnants of the Nitto stem are in the pic below.
I would not wish this problem on my worst enemy. Well, maybe my worst enemy, but not a fellow BF member.
I hope you achieve your goal. I'll share any information I can with you about this experience.

I hacked off the stem so I could just that. I have the steer tube clamped in my work stand with the end soaking in a bucket. The torch is plan B. I'm going to try heating the steer tube after I've iced the stem with dry ice.

I have had good luck freeing stuck parts, not necessarily stems in forks, with cooling by inverting a can of compressed "air", the stuff you clean your computer with, then follow with a gentle heating with a torch or heat gun. The steel and aluminum expand at different rates, so this should help break it loose.

Don't heat the threads.

Even though it says https://www.sheldonbrown.com/brandt/stuck-stem.html that ammonia doesn't
work, I found that pouring a small amount of ammonia down the
upside down headtube and waiting 2 hours that the stem turned pretty easily.