Are the valves all free? A stuck valve will keep it from turning over right up until you bend something...
Take a big rubber mallot and hit each valve and see if you get them to bounce. If you find one stuck you can loosen the rocker arm up so you can remove the push rod. If you wanted you could just remove ALL of the push rods to take them out of the picture. Make sure you tag them so they can go back in the same hole.
Mike B
