Ok, so i just bought a d16y8 to build over winter for boost for my EF Sedan, but thats besides the point. I started pulling it apart tonight, and found a "Ball" in a hole in the head, and it appears coolant has been leaking out of it for sometime, and has corroded in beetween intake ports 2 and 3 on the head. It was slightly covered by the intake mani gasket. What is this ball for? Is it kind of like a freeze plug or something? Was it leaking coolant? Or did water just get in and set under the gasket? Heres a picture, thanks everyone!

 

The ball looks like it's cast into the head. Nothing to be concerned with. I would say you managed to get some coolant in there while you took it all apart.