Just part of the combustion chamber. It looks dark in the phot because of the light. I’ll ask Scott next time I’m over there about it.

Looks like marker pen to me, Steve ? Maybe a reminder for the machinist that he has done some work ?

I asked Scott when I stopped over. He just roughly cleaned up the bowls and those were spots in the chamber he hasn’t touched yet. When he does the final port and cleanup work those spots won’t be there.