The internal springs inside the lifters should keep the plungers topped out against the retaining rings. Sometimes I've found that it's necessary to be able to see the plunger while you're making the adjustment or it's possible to force it all the way to the bottom of its travel. The internal spring is very weak. That's easy to do on a V8 engine with the intake manifold removed, but it would require pulling the side cover on a six. A 20 thread per inch adjusting screw will only move the pushrod down .050" in one turn, so the inner plunger is usually less than 1/16" below the retaining ring when it's adjusted correctly. Non-adjustable rocker arms for V8s like those used on Pontiac, Oldsmobile, Ford, etc. require different length pushrods to adjust lifter preload, usually +/- .050"
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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