I've got myself a mystery. I just finished installing new head gaskets and studs on my 2005 F350 6.0 After torquing down the studs and pedestals I went to make sure the engine would turn over by hand before going any further. Much to my surprise I found that I couldn't turn the engine over completely. I found I had about 300 degrees of rotation back and forth before the engine would lock up solid. After some investigation I found that the #4 exhaust valves were hanging open for some reason. FULL DISCLOSURE: During initial assembly I had carelessly and inadvertently assembled the #4 exhaust rocker arm with the push rod end sitting on the edge of the rocker arm cup and had torqued everything down, but then noticed and corrected this situation before trying to turn the engine over. Finding the engine locking up, I triple and quadruple checked to ensure all the bridges and push rod tips were properly seated. What I noticed is that the #4 push rod was sitting a little higher than the other ones when the lifter should be on the base circle... and therefore the exhaust valves were open a little bit. Weird. I took the stud and pedestal off and ensured I could turn the engine over properly and found I could. I turned it over probably 8 full rotations or more. I reinstalled the pedestal and once again found that the #4 exhaust valves would get forced open when they shouldn't be open (lifter on cam base circle - known because I had the #4 intake valves open a considerable amount). So I start to wonder what could possibly cause this. I theorized that possibly the lifter had rotated somehow, but discounted this after researching how these lifters are secured in place on this engine (Although I wrenched for a number of years as a mechanic - years ago, I never did any work on diesel engines). Maybe the lifter somehow got pumped up? Out of ideas I removed and reassembled the pedestal once again and to my surprise everything seemed kosher now! ... without knowingly fixing anything. The #4 exhaust valves were now closed and the rocker arm had the same amount of movement as others where the rockers were on base circle. I turned the engine over a dozen or more times ensuring that everything seems okay and it certainly seems so now. But the question remains... WHAT ACTUALLY HAPPENED TO CAUSE WHAT I EXPERIENCED?

 

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