I spent 1 hour looking at youtube videos on "how to remove a broken bolt" and came a cross really nice, detail, right in your face shots when the dude extracted the bolt...at least one of those vids was of an engine head. I got to extract one out of my exhaust bolts too. Good thing thought it broke half way in and I can still screw/unscrew enough in there...

 

that exhaust bolt? soak the heck out of it in Kroil before you even start. 2-3 applications (don't need a lot, no point in it running off) and overnight, THEN try and get it out.