.020" preload won't work if you're not using a race hydraulic tappet. plunger travel in the tappet should be around .210". the preload needs to be around 50% of plunger travel. if you have adjustable rockers with 3/8"-24 thread adjusters set the preload between 1 1/2-2 turns. that will give you somewhere between .060"-.090" preload. treat .060" as a minimum. factory pre-load with non-adjustable rockers was at least .100". a performance hydraulic cam will make a little noise due to the fast closing ramps and that can't be adjusted out. setting the preload to .090" should make a noticeable difference.
I've never seen any stock production hydraulic lifter or after market Hi Po, not anti pump ups, that wanted to have anywhere close to .100 or more preload.
I remember when the first Hi Po anti pump up race hydraulic lifters came out in the mid 1970s that the instructions said to set them at zero preload to .0020 lash
I was dyno testing several NHRA legal 340 stocker motors and ended up testing them at .0020 lash and then at .000 and again with right at .010 to .015 preload on them using stock blueprinted ductile iron rockers 3/8 inch X 24 thread adjusters so a 1/4 turn preload was right at .011 lifter preload.
I have heard of guys recommending adjusting all the travel out of the lifter so it is bottom out, I won't do that
