There's two dozen ways to adjust lifter preload, and they ALL work if the guy doing it knows what he's doing. Some ways are more-complex than others.
The more complex the method, the more it's intended for solid lifters that need lash rather than hydraulic lifters that need preload.
The BIGGEST PROBLEM folks run into is when they "spin" the pushrods looking for "zero lash". THIS IS A REAL TROUBLEMAKER. Your ability to "spin" the pushrods varies depending on how strong your hands are, whether your fingers are oily, and how stiff the springs inside the lifters are.
I've seen guys "spin" the pushrod while tightening the rocker adjuster nut, to the point that the lifter plunger is TOTALLY collapsed, then they add preload which means the valve CANNOT close. Engine runs rough, or doesn't run at all.
DO NOT "spin" the pushrods. Pull up on the pushrod end of the rocker arm, and let the rocker arm drop down onto the pushrod. You'll go from having actual clearance (rocker arm flops up and down) to tightening the rocker adjuster nut gradually removing that clearance (rocker flops progressively less up and down) to achieving "zero lash" (rocker is just at the point of having no free-play "up", but may be FORCED down against the spring in the lifter)
"Zero lash" is the prime target, it's what you MUST achieve in order to get consistent preload.
Once you have "zero lash", you merely add "your choice" of preload. Some guys like 1/4 turn of the adjuster nut, some guys want 1/2 turn of the adjuster nut. For decades, Chevy said to add 1 full turn of the adjuster nut. I've seen OEM hydraulic lifters with more than 1/4 inch (250 thousandths) of plunger travel. I've been sold hydraulic lifters that had about ten-thousandths of plunger travel, and no warning on the box that they're reduced-travel lifters.
The absolute fastest, simplest, easiest way to set lifter preload: Crankshaft can be in ANY position, does not have to be at "0 degrees" as shown on the damper/timing pointer--but that's recommended. Otherwise you have to mark the damper manually with a paint stripe or yellow crayon, or something.
Loosen all rocker arms so they have free-play.
Tighten all rocker arms so the free-play is gone, but don't go beyond the point of eliminating free-play.
Rotate crankshaft exactly one full turn. Either go from "0 degrees" back to "0 degrees" as shown on the damper, or mark the damper with a paint stripe, and turn one turn so the paint stripe is back where it was.
SOME of the rocker arms (fewer than half) will be loose again--having free-play.
Tighten ONLY the loose ones so the free-play is gone, but not beyond. Leave the "tight" ones alone. All rockers are now at zero lash.
Tighten ALL rocker arms "your choice" of preload. "Your choice" varies depending on the available plunger travel of the lifters--
know what you bought!
Put the valve covers on, and have an adult beverage. You're done.
For the record, "soaking" lifters in oil is a TOTAL waste of time. It does NOTHING useful. If you submerge the lifters, and then pump the plunger, you might get the oil inside the lifter. When it's me, I use a pump-style squirt can, and fill the lifter with oil (ATF, it's thinner) under pressure. This means I can verify the leakdown rate of the lifter, and it proves that the lifter will pass oil to the pushrod seat. It also means that when I add preload, I'd better do it slowly so the lifter plunger has time to bleed-down.
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