Lifter preload...more or less?
I also as a carpenter find it hard to believe that 1/16 - 1/8 makes that much of a difference
I have a saying...
Close enough for concrete. (+/- 1")
And along with that goes
Close enough for wood (+/- 1/16")
And
Close enough for metal (+/- 0.002")
(Just numbers I use for example)
What I'm getting at is in the concrete world close is perfect.
In the wood world really close is perfect.
But in the metal world you better be dead nuts on or you will have problems.
Imagine if you used your 0.125" for bearing clearance!
Also just like everything else, metal grows when it gets hot and in an engine it gets much hotter than wood or concrete.
My 273 has mechanical lifters and if the gap is set too loose the lifters rattle. Too tight and valves will not be sealing when the engine heats up. The engineers spent decades learning how to compensate for all the growth that happens in the engine.
So yes a few thousandths makes a big difference.
With hydraulic lifters and not particularly high rpm you can get away with pretty close.
But as pointed out if the lifter pumps up and the lifter piston is too far compressed... Piston meet valve.
Just my 2 cents
