1969 426 Hemi. Have a Comp Cam Hydraulic Thumpr roller cam and lifters, using stock rockers, have 40lbs of oil pressure at idle.


Problem is I am getting some lifter tapping across engine. Talked to Comp Cams, need .020 to .040 preload. Turned engine to correct position to adjust each rocker, first they said go to zero lash and half turn.

That helped a bit but still have tapping, then they recommend adjustment zero lash and go one full turn, I tried that and still have some tapping, it was a small improvement.

Now they are saying with this particular cam and lifters I have go to zero lash and then go at least one and a quarter turn.

I'm getting a bit nervous going that much. I myself in the past with other motors (other then Hemi) never had to adjust preload on a hydraulic that far, usually half a turn max.

Are the factory adjusters on a Hemi a finer thread and require that much turning?

Thanks,
Wolf