guys 
The Bentley manual now states that preloading is optional becuase of all the problems preloading can cause. These problems can include low power hard starting hot and lifter clater  
see my article on my web site called Boston Bobs history of the hydraulic lifter
Bob Donalds 
 
clarence wrote
Need to adjust my lifters, 2.1 water cooled.
Bentley, 15.29  doesn't say hot or cold just 2 turns clockwise after the
adjusting screw touches the valve stem.....

frank wrote
The .010 or .020 "real measurements" are for mechanical (i.e. solid)
lifters.  Hydraulic lifters are commonly set using a number of turns beyond
zero clearance.