Preload is not lash. The opposite really and I think it's important to make that distinction when we talk about it. What we are talking about is the distance between the top of the lifter's plunger or pushrod seat, to the bottom of the plunger retaining clip.
"Counting the turns" is a general way to do it. It's dependant on the thread pitch of the adjuster and that can vary, especially with the cheaper offshore stuff.
The type of lifter is important to know:
- Hydraulic factory type lifters are forgiving and can ususally run well and quietly with preloads as short as .020 to as much as .060. These are generally used with most older cam grinds, and the new grinds that are milder cams but still fast rate.
- Anti-pump-up hydraulics are designed to not compress as much under working load because the compression is what causes loss of control of the valve, or valve float. These lifters take less preload and the spec will depend on the lifter manufacturer. Generally you want a smaller window. I use .010-.020" Any more and you may end up hanging valves open. These are the "optional" numbers in Comp for the faster rate medium to large camshafts, all of Lunatis, all Bullet, and IIRC all Hughes fast rate cams. These, even when the preload is right, may be noisey and sound much like a solid lifter with too much lash.
-Variable duration lifters are anotehr aftermarket deal to try and get some compromise between big cams and "street manners". Again, concult the manufacturer because they will be noisey but still be set right. I don't use them so I can't tell you guidelines...lol. If you need variable duration lifters, you needed a solid lifter profile as far as I'm concerned.
One other note.. If youve ever used header lock bolts on the heads, the washers on them will sound like a loud lifter until the bolt backs out and preloads them.... Usually takes 5-10 heat cycles.