trick to removing valve covers or EGR valve?

[VileZambonie]

Hydraulic lifters bleed down regardless of setting and preload adjustment. So saying, "oh these are loose and shouldn't be", then tightening them will result in valve clearance that is too tight. You have no idea how many times I've had someone say the same thing and try tightening them up, usually bending a pushrod or creating other issues and then calling me to the rescue... If they aren't noisy, leave it alone.

[JohnnyPopper]

I stand by my  observation:

In a clean and properly adjusted hydraulic lifter, the spring preload is enough keep the rocker snug to tight, not flopping around.