Originally Posted by Smkndzl

Not long ago, I had to inspect a Cummins ISX runaway and it had dropped a valve also, it was on the dyno and the tech said it just ran away for no reason. they had just replace the head gasket. after inspecting it the engine would not rotate, it had coolant in the cylinders, had the tech remove everything on the head, looked at it again and found a hole in the intake port, pulled the head off , still could not see anything and after inspecting it, and it was buried in the head casting a 19 mm deep socket, ask the tech if he was missing one , of course not he said LOL , I handed the one I found in the head to him and told him check again. what he did was left it in the head after putting the top end together and it got jammed between the cam and head, broke completely thru the casting into the intake and thru the intake back in to the head and sure enough the ISX head hold about a gallon of oil in the galleries and suck it thru the hole. so it wasnt the valve that cause it to runaway. anything is possible , but have never seen a runaway from a valve drop only.