Originally Posted by dddd

For the stuck stem quill, I've had good luck with heating the stem and then letting it cool.

The heat expands the quill lengthwise which helps break much of the bond within the steerer.

I will apply a penetrant as the stem/steerer are cooling, having cooled down below the smoking temperature.

A lot of heat can be applied before the head tube starts to get hot, but the handlebar will try to pull heat out of the stem.

If you can secure the crown in a vise then you'll more easily apply twisting force through the quill.