I have a 93 7.3 1 ton idi the truck was driving great then started making a loud chattering noise and losing power I pulled over to check it out and it wouldn't crank back up you can turn it almost a full rotation with a breaker bar on the crank but then it just hits a hard spot I pulled the valve covers but all springs were still in there place what's going on here? Thanks for any help.

Sure you didn't throw a rod? The valve springs could stay in place with a dropped valve since the rocker arm and valve keepers are still in place. P
.