ok so right now i am putting back together my 5.4, i have all the internals in and the heads w/ cams, valves and what not. so i put on one head check the timing marks like 4 times turned the motor over to make sure no valves hit. none did it would let me just keep on turning it over. so i put on the other head, checked the timing marks, all lined up, looks good. go to turn it over to see if any valves hit, turning it over and about 180° later it stops and i dont want to keep turning it because i dont know what might be stopping it. do you guys think that it is ok? how much force is needed to turn over the motor? i check all the timing marks every thing is great. WTF?

 

You screwed up turning over the motor while only one head was on. Sounds like you are 180 degrees out.