Although I have many years experience with engines, they’re mostly old solid lifter, usually flatheads. Now I’m working on my ultra modern 84 slant 6. It has been sitting for a couple months, and when I took the valve cover off, it doesn’t look like any valves are open. Unless the cam has evaporated (it was running when parked so I’m doubting this) all I can figure is that the hydraulic lifters leaked down and let all the valves close? There was some small spring tension on the rocker shaft when I unbolted it, but no valves obviously open.

There is a fair amount of lifter travel, but even fully collapsed there should have been a few valves partially open and this is supported by the pressure on the shaft you describe.

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Joshua