Originally Posted by
HIPCHIP
Have you tried soaking the stem area in WD-40, or some other penetrant? Sometimes a good soaking and working it will get the rust to break free and then you can use a wrench or other things to get it to start turning, then soak it more, etc. I had to go that on an old BMX bike once and it took a couple of days, but it worked.
I've tried the penetrating oil (pb blaster) but this is an aluminum stem stuck on a steel fork tube that's going to require more than that.