I was idling along this morning and I heard a random clanking noise, each time the engine would stutter like it was missing. Then 5 min later this horrible high pitch scrape for half a sec, and it locked up. Got towed home pulled the plugs, one looked like it had rust or mud on it. I grabbed the flywheel and suddenly it was free. All 6 have compression, I put the plugs in, it ran perfect. 2 min later it randomly started making clanking noises, metal to metal contact somewhere. I noticed that the flywheel is moving up and down about 3/8", and is bolted tight to the crank. Whenever it moves up, it jams the engine. .....anyone every heard of this problem? Is there a thrust bearing that could have gone bad?