Iodine works better than penetrating oil, but now its oily, the iodine won't get down where its needed. A good trick is to make a fitting for the spark plug hole that'll couple to a pressure washer hose. Zap it with a few hundred (thousand?) pounds of pressure every few minutes, alternating cylinders, and you'll be amazed at the results. If you have another tractor with hydraulics, you can hook up to all four cylinders (with dual hydraulics) and things will happen in a hurry.Just don't get too chummy with the old engine when you hit the levers, old iron can shatter and scatter. If the valves are stuck open, make a plate to block off the manifold surfaces.It WILL turn over, but it might not be any good anyway.Its possible to bend rods, cranks, even bust heads this way, so use your head and don't get rammy.