Checking cylinder head flatness?

[Outdorsman]

http://www.dsmtuners.com/forums/articles-engine-fuel/341627-how-check-head-warp.html

I read that but one thing that gets me wondering is the fire ring grooves. I don't really comprehend? Is it supposed to be flat or deeper than the rest of the head? At what point would I need to get it resurfaced? My car never overheated, just blew between two cylinders.

 

[BogusSVO]

A fire ring is when the sealing ring around the cylinder bores of the HG dig into the aluminum of the cylinder head, It also happens to a cast iron block.

A straight edge and feeler gauge will not show this, due to the width of the fire ring, the feeler gauge will bridge over it.

But you should be able to feel it with your finger in most cases.