If the intake is off, you can see and measure how far down the cup is in the lifter.
Otherwise, and with empty lifters, it takes a delicate touch to find the starting point. I remember one time targeting 1/4 turn preload, with empty lifters. Hah, that wasn't the best idea I ever had............ It wasn't long and I had tickers in there. So I just cranked in another 1/4 turn to the tickers, and a couple of weeks later,different ones were ticking.
Ok, I like to think I'm not a dummy, so I learned that my 1/4 turn target was not realistic, and started all over, but increased the preload to 1/2 turn. Problem solved.
On the next build, I started with pumped up lifters,and set the preload before the intake was on,..... so finding the zero-point was a lot easier. And I started with 1/2 turn.
Using pumped-up lifters tho has a different issue. Sometimes when you crank in the preload,the lifter does not bleed down, but instead the valve opens. So you have to trust what you are doing. No matter, by the time you finish setting all of them, some or most will have bled down....... BUT, you have to make sure that your preload is less than your piston to valve clearance, or you could end up driving the valves into the pistons, as you rotate the crank. This is usually not an issue, cuz who builds to that tight a PV tolerance?
I think the adjuster threads are 32 threads per inch, so 1/2 turn is .0156 preload at the lifter times the effective rocker ratio, might be as much as .0234 at the valve(with a 1.5 ratio) if the lifter does not bleed down. You have to know your PV clearance because because the lifter manufacturer might spec a lifter preload of .080 ; Which, if the lifter would ever fully pump up, would be .128 at the valves with a 1.6 ratio,and almost guaranteed to bend a valve. At 32 threads per inch, .080 preload is 2.56 turns.
My PV clearance is tighter than .128, which is why I run only a 1/2 turn preload. I like to buzz my engine up to 7000/7200, and if a lifter, set to .080 preload, should ever pump up on the trip, that would be an instant bent valve, actually probably at least 8 bent valves, and of course, the engine would lose all pressure and not idle, stall, and fail to restart. But the 1/2 turn is .050 at the valve in my combo, and so with say 8 pumped up lifters, I'm ok. The engine still would not idle, but if I kept her revved up a bit, she'd bleed down pretty quick. Proper springing of course should eliminate pump-up in the first place.
So after this essay, you might think that setting the preload with pumped up lifters is a worse idea than setting it with empty lifters. And for a newbe, I'd have to agree with you.
