If you have a sticking valve, try to remove the rocker arms and tap on the valve with a hammer to see if it can break free, but not hard enough to bend one....
I just tried what you recommended, had a piece of wood and a rubber mallet. Tapped lightly a few times and heard a light thud sound, put everything back together and now have 0 compression on that cylinder. Not real sure what I did but don't think it was good.
