Just did a bulletproofing to my 6.0, even upgraded to a bigger cam, but nothing wild, and new head. Followed the ford service manual to a T. So far I have all the exhaust rocker arms on the driver side broken, looks like the push rod went up, but the valves didn't, snapped the rockers in half. Intake rockers are fine, just on the exhaust side. Haven't open the passenger side valve cover yet to see what's broke over there. Any ideas on what would cause this? And yes I did rotate the engine so the dowel on the crank was at 6 o'clock before installing the rockers.

 

I wonder if the cam timing is correct? I also rotate the engine by hand before I try to start.

 

Yep cam is timed right, got the special tool to install new cam, dummy proof. We suspect that we didn't have the pushrods seated correctly, cause we did not rotate the engine by hand after install.