I used to have problems with them until I started to tighten and loosen them half a dozen times. This allows them to seat much better.

I do the same thing with new rocker arms and adjuster jam nuts.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)