Did you just move the crank, or your turned over the engine 90 degrees? how did you verify the belt condition is ok? looking at just the top half doesnt typically do it, turn it over by hand and make sure it is all turning appropriately. The belt can look fine, and the cams can be in perfect time, but the teeth could all be sheared off the pulled around the crank gear and the bottom end is just spinning.


it could be the teeth on your starter gear are bad, and you just happened to be in a spot it didn't work. or your started was stuck on the fly wheel and turning it over released it. etc.