On some engines, if you fit roller rockers, you can decrease the gap slightly. No idea if that is true on the S&S.
Mind you, the tappet gap on the JAP LTOW is a whole 2 thou, and they are still noisy.
So the rattle cans
are often left off.
I believe that running clearance is greater than that, but when cold you do set them very close. When warm the motor expands and the valve lash increases automatically.
As far as the valve noise on an S&S motor, the newer Harley Twin Cams have a very similar problem. The cam profile has a lot to do with the valve train noise. On some of the Harleys with S&S lifters, they over tighten the push rods to add more preload and this does help in some cases.
Typically roller rockers in automotive motors are noisier than non-roller rockers. S&S I believe uses GM V-8 rockers, cheaper to buy something that already works than to make their own.
