CB750F SOHC - Broken spark plug stuck in head

I've just picked up a 1975 CB750F that's been sitting for a few years. Bike is in decent shape but there is a broken spark plug stuck in the cylinder head. I've tried an easy out to remove the broken plug but it won't budge (I actually twisted the easy out). I've filled the entire cylinder with loosenol and let it soak for days but the plug still won't budge. Any ideas for how to get this F'er out or am I pulling the motor and removing the head?

Any tips on what to do on the 3 remaining plugs? I'd imagine they're seized as well.

Just pull the head and soak them from the inside as well. Should be able to lock a pair of vice and twist out. You'll definitely want to check out the valves and pistons to make sure moisture wasn't getting in and rusting those too.

if the frame side rails have been cut as a lot of them have you dont have to pull the motor

to pop the head

once you have the head off dont screw with it take it to a machine shop and have them get it out

Frame side rails aren't cut and I'd prefer to leave them that way. Guess I'll be pulling the motor.

Thanks for the tips guys!

Chances are if the plug(s) are seized, you need to pull the head off anyhow.

But if you think it will run as-is, and it seems to turn over OK (it should run on 3 cylinders if it's going to run at all) then haul it to a proper shop and let them give it a try.

Heat will expand the aluminum head more than the steel plug, so that always helps - along with impact wrenching. But if the plug sheared off when someone else tried to remove it, chances are the only way to do it cleanly is to pull the head. Otherwise you're going to end up with crud in the cylinder anyhow and will need to pull the head regardless.

Yeah, I think I'm just going to pull the motor. I hear that it's not a fun or easy job on these bikes but it seems like that's the "right" way to do it.