what about clearance between retainer and valve guide/seal? what about possible coli bind? How many threads of adjuster are exposed under the rocker arm? You don't want too many, because that's not good, but you don't want too few either because the cup edge on top of pushrod may contact rocker bottom at extreme lift and come out of the rocker socket. There is one very remote possibility I can think of: if you had too high of an oil level the crank could whip the oil in the sump, and aerate the oil, collapsing a lifter. Conversely, if you pump the sump dry at high rpm's, you can collapse a lifter(among other things).