Everybody has their favorite penetrating oil, but I like P’Blaster. Start by shooting oil down into the cylinder through the spark plug hole, and don’t be shy – use a lot of the stuff. Wear goggles in case the penetrating oil sprays back and hits you in the eye. If you have the patience for it, spray some in every day for about two weeks, followed by gently tapping on the cylinder wall with a hammer handle. This sets up vibrations that help the oil penetrate between the rings and the cylinder wall. After soaking the engine for a while try rotating the crankshaft. If you’ve been patient, and if the engine wasn’t too badly rusted, it will usually break free and rotate. If it doesn’t, hit it with more penetrating oil, and make sure you use enough. I’ve found that about half a can per cylinder is right. If it still doesn’t rotate after four weeks of daily treatment, it’s time to resort to more serious measures.