Originally Posted by Chombi

You need to break the corrosion between the stem and steered tube. Many had been successful using "Freeze-Off". Do a search and you can find out how to best use it. A couple of years ago, I was able to release a really badly stuck stem on one of my bikes by using Freeze-Off. Discovered the stuff after using all sorts of other penetrants, including PB Blaster for about a month of soaking, and careful twisting and pounding without success, till I used the Freeze-Off...and the stem came off only ten minutes after I used it!