Missing plug?

[TobyT2015]

Hello all. Have a question. I own a 1972 Chrysler boat with a Volvo B30 AQ170A and I am in the process or restoring the boat. I have been going over her stem to stern and I noticed that a silver disc lying on the deck under the engine. I found an empty "hole" on the starboard side of the engine under the manifold. Could someone please tell me what this is? I would appreciate the help.

 

[dannys2004glastron175mx]

That's a core plug . you need to install a new one or water will leak from it .

 

[jerryjerry05]

What you have is a freeze plug or expansion plug.
In the hole? is there a metal plug? Or is that the inside of the block?
The plug can be set back in the hole and use a center punch or a round tip drift and hold it in place,
then hit with a hammer to spread it out.
Use a good sealer on the edges.
Since it "fell out" I'd check the others and see if they are still in?
And look for freeze cracks on the rest of the block.
Usually
The parts still available here on this site..192212 About $16