driver444

My friend's 2006 expedition just quit. He was driving, and heard a continuous tapping noise from the engine for a minute or 2, and then it quit, just like somebody turned the key off. Engine light came on. When he went to restart it, the engine went through cycles where it turned over easy, then hard, than easy etc, like it had compression, then not, and back and forth. No start.


We did an air test on the engine. Air in-air out. So I figured it jumped timing, and/or bent valves.


I'm far more knowledgeable with the old pushrod motors, not these.


My question is, is this motor a zero-clearance motor? Will a piston contact an open valve if it jumps timing? What are the chances that the bottom end is still ok? I just thought I'd ask before I bother to pull a head, and attempt to swap heads.
Thanks