Originally Posted by CRuby

OK. Time to eat crow!
I took the valve cover pictured above (post 25) in to the materials lab where I work & the failure analysis metalurgist looked at it under much higher magnification than my 10X jeweler glass. Most of the long red-dashed lines regions in prior pic are not cracks, but are evidence of casting parting lines. SloopJohnB, +1. However, there are several areas that branch off the parting lines that are really cracks. These are branches off red rectangle below cyl. 6 (on right), & on hump for TB on left side of pic (not marked). What I was considering secondary striations are also not cracks, but rather appear to be slight scuffs/scratches done by some some external operation. The metalurgist speculated that the scuffing is only evident adjacent to regions of this parting line, likely because of finishing process used to buff off the excess mold line during manufacture.
Anyway, I thought I should followup on this topic, since I left it stating I believed they were cracks. Most (but not all) of them are not.
Crow tastes like chicken.