I rebuilt an f head 134 (bored to .60, rebuilt the valve train, milled crank, new pistons, bearings etc.) I got it started and drove it around town for a couple days and it ran fine. Yesterday I got in it to finish breaking it in, so I got on the highway and was doing about 50 mph after a couple miles the engine started rattling and stalled out (power just went to hell) I pulled over and let it idle and it picked back up for about 10 seconds then the same thing only this time when I pulled over it died and I cannot get the engine to turn even with a breaker bar. Took the oil pan off and the pistons and cylinders look fine all the valves look ok I pulled the caps off the rods and mains and they look fine. I was wondering if the flywheel or pressure plate might have come loose I torqued the pressure plate to between 20 and 30 lbs., or could it be something else Im really stumped and dont want to pull the motor if i dont have to.