I pulled off my valve cover to adjust my valves, I noticed this was missing. I did a full rebuild on this engine 10000 miles ago, everything seems normal (aside from loud valves) I looked at my manual, it looks like it may be the oil control oriface.

If so what does it do? Is it bad that its missing?

Engine is a d16z6

 

On my Y8 head there's a bolt in it.



The oil control orifice is in the back center of the block/head. Smaller hole on the mating surface in the picture (Y8 Block):

 

So... I got curios and pulled out that bolt. It's about 1/2 inch long and just a plug. Looks like an oil passage inside. VTEC related I guess, but all that VTEC stuff is still evil magic to me.

 

I found the bolt, looks like it backed out and was just laying next to a valve springs. I cleaned up the threads and reinstalled it. I wonder if that Opening would affect oil pressure?