408 hyd roller, too much spring pressure?

Swede408 said

I do have a bit of noise even after start up, but not nearly as loud as on startup with some of the lifters drained.
I don't really get what causes this. Is it the check valve in the lifter that can't cope with the pressure, causing the lifter to bottom out?

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The cause is poor quality control by the lifter manufacture.
I had this same issue on my 340 with a set of hyd rollers from Comp Cams, I tried every preload you could think of nothing changed, Comp replaced them under warranty with a set of solid rollers. I sold those and replaced the hyd rollers with a set of Morel solid rollers and kept the same springs. Time will tell but I have around 250 miles on the new solid rollers and no issues.
Just search "isues with hydraulic roller lifters" and watch your computer light up.