Have tried:

1. WD-40
2. Hitting expander bolt with small hammer
3. Hitting expander bolt with big hammer
4. Throwing a tantrum.

Any other techniques from back in the old days or do I need to take it to the LBS?

has the wedge bit dropped when you hit the bolt?

if not hit it harder.

Block of wood on top, smack downwards, to break any corrosion bond.

Turning upside down and spraying WD40/Plusgas/Penetrating oil down steerer can help. Leave it overnight. Sugary pop like cola can do this too; dissolves the oxidised metal.

1.Caustic soda and water
2.fork crown in vice twist bars
3.cut top of stem off remove forks then heat the steerer tube and bash out remains of stem

Loosen the bolt 1 full turn and try turning the bars very carefully to see if it moves. No dont. You said you had a tantrum so that might be a bit risky!
Buy a can of Wurth Rost off ice. The first few times i used it on car parts i didnt think (or know) if it made the job any easier but i was using it this afternoon on manifold studs in an engine and it seems to be doing the trick compared to the ones i never sprayed earlier in the day. The nuts are coming off well and not staying seized onto the studs.

Is the stem stuck or the wedge? If its the wedge the remove stem completely
And take fork out of frame. Spray loads of wd40 top and bottom. Give it a while to work then get a steel tube from the bottom and smack it (rest the headtube on a block of wood on the floor). Got
One lose the other day doing that

assuming you are hitting it from below [ up the steerer via the hole in the forks with the bolt fully undone I can only assume you have not found a big enough hammer yet

They rarely stick?

When you undo the stem bolt it should rise up, is yours?
Then you tap it down.
Easier to do when the bars are attached and the front wheel is in.
All through the 60/70/80s and early 90s I had no issues, but the parts were always greased.

edit, if the wedge is stuck in it’s fixing place the stem won’t come out. You don’t need to undo much of the bolt, two turns and a tap should do it.

Yup hit it hard and without any wood etc that would soften the blow. Support it on concrete too for more shock.

lots of little taps, metal on metal-you want to ‘shock’ it loose.

Very confused here.

The wedge is way smaller than the inside of the headtube, it can’t get stuck on it’s own.
The stem has one or two slots, the wedge when tightened travels up the inside of the stem forcing the faces out. the wedge does not contact with the frame.
Hitting from bellow with parts in place will tighten it further. You release it from the top so the wedge is left dangling in the frame attached to the long stem bolt. Then remove.

Ahh

Just been told that ‘modern’ quill stems have a weird angled sliding wedge ? But even these should be loose in the frame.

It’s the stem that is stuck as I can undo the bolt. From what I understand (and correct me if I’m wrong) the stem is held in place by the friction of the wedge. Hitting the bolt knocks the wedge down thus releasing the friction.

Anyway I’ve left a load of WD40 (and a bit of beer as I don’t have any coke) to soak in overnight to see if that helps.

Then I’ll find a really big hammer.

Thanks for your help guys.

What stem is it. See older ones with splits would spring back into shape once the wedge was loosened.

I got hold of an untouched 1958 road frame, undid the bolt and out it popped?

yes you should hit from above sorry I thought just the wedge was stuck and the stem removed

Undo top bolt a good few turns then thump it downward really hard when it drops it will “free” the wedge and should remove anything else and the while thing is rusted so hot from below

Bike is from late 80s/90s I would guess and the stem is a 3TTT