I have a 1942 Chevy truck with a 235 engine in it, on may way to store it for the winter a loud rumble and vibration started to happen. I put in the clutch and shut it down right away. Check the driveshaft and u-joints all was ok. Put in the clutch and restarted the engine and the rumbling and vibration came back. I pulled the plugs and found all pistons moving up and down normal. Went under and pulled the flywheel cover and found if I turn the engine over by hand with the flywheel it moves about 1/2" before the harmonic balancer starts to move. Any ideas of what could be wrong???????? Would like to talk to someone over the phone if possible but will take any suggestions you may have. Thanks!!!!!!!!Send me your number 1-262-392-2989 or [email protected] Marv.