Think that the original military multifuel design is to have ALL the lube oil drain to the crankcase when shutdown to ease restarting in frigid temperatures. It was designed a a tactical military vehicle for service, even in the arctic. That is why we put the modification of oil filters with anti-drain-back feature.
Just a thought.
You only drain the oil for extreme long term storage (years). What the manual says is to install "new" oil and run it for a few minutes, then shut-down the engine. Then loosen the rocker arms to allow the valves to close. I would only loosen the rocker arms if I was going for a few years storage myself. Also on long term storage they recommend you drain the fuel tank. I wouldn't do that today. With the advent of modern fuel stabilizers like "Pri-D" and "algae" busters there is no reason to, and plenty of reasons to keep the fuel in place. Like preventing rust in the fuel tank and the fuel system in general.
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