EOIC vs. "The Chart"....

Mopar Sam said

A couple of things that can slightly affect it are, sideplay between rocker pairs, were the rockers in the same place side to side. If ductile rocker arms, how much wear on the tips? And a slightly bent pushrod will affect the lash as it rotates.

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So maybe that's the difference. Turning by hand doesn't let things move and 'center up' the way they do when bumping the starter...which would be more like what's happening when the engine's actually running. We are only talking a couple thou, so I could see that...