If the head cracked or the head gasket gave up the ghost and let the cylinder fillup with water it would lock up tight as you describe. If you remove the head you will probably find a very rusty cylinder. I bought a truck really cheap because the engine was frozen and found a nut had been dropped down the intake manifold and wedged a valve open. I carefully removed the nut put the head back on and promptly sold it for about 6 or 7 times what I paid for it. Jim
