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Message: [QUOTE="Maryland dieselnick, post: 1273393, member: 22661"] Sure, the trucks that have this happen have guides that have inside diameters that came thru smaller than they should be. When the valve stem is inside of it, there is not enough room between the stem and guide to accommodate the normal film that builds up on stem due to exhaust gasses escape venting up that guide any and all times the exhaust gas back pressure exceeds atmosphere pressure, which is normal for all engines, AND still have adequate clearance to additionally accommodate the expansion that occurs due to a $7 and change valve and this guide gets blasted while the valve is open during the exhaust stroke with extreme heat from the injector firing on that stroke. This valve has a spring trying to pull it closed while open. When the thermal expansion reaches its max, it causes what known as thermal expansion stiction. Thermal expansion is not a "seizure" in the classical sense. It is "stuck" While in this static state due to this stiction, the spring still has stored energy within itself trying to pull that valve closed. It is on the razor line of remaining in this static state and having the spring pull it closed. Because it's on that razor line, it offers little resistance to the piston pushing it out of that static state. Due to the valve offering little resistance to this combined with the valve geometry used, a straight up motion, the piston puts virtually no lateral force on this valve, which would be a catastrophic event immediately, this is not the case with the 6.7 and is why besides the violent bucking and no power, it tolerates this for a while. The new head has new guides that hopefully are ok ****** if the tech does not verify the new heads guides are not too tight on the new head, the truck will be right back****** [/QUOTE]