Ok i have a huge problem and know idea what caused it.
I have a 81 5.0 Ranger/F-150 and the motor shut down drivin 55 mph.
I pulled the the timing cover off thinkin the timing gear busted. Negative it is in fine. I turn the key to start and nothing moves on the crank shaft just kinda pulsates. Look at the fly wheel while engaging the starter and fly wheel turns no problem. Any one have a clue what could of happen.
My intial thought was the crank shaft broke but there is nothin high perfomance on the truck just aluminum intake and 4 barrel carb. Please any advice would be grateful
Thank you

 

I've seen just this problem before on early '80's Fords. It's not common, but I'll bet the crankshaft is broken. I know it's supposed to be extra hardened and the like, but I saw this exact problem on a '81 T-bird with a 4.2 (same block) and it beat me up till I took the pan down and that explained everything.
This assumes that the starter is actually spinning the flywheel, of course.
Good luck!

 

It was my worst case sceniro thought and was my first thought when it happen. Thank you so much for responding to the post it was a great help. Looks like i got a lot of work ahead of me. Thank you again sir