Exhaust leak before manifold

[Phylarch]

Ok guys, I've got a question.
I have a 1979 Marquis Riviera with a Mercruiser 470 inline 4 banger. There is an exhaust leak on the aft section of the head. This leak is a 1/2 inch perfectly round , but not threaded hole facing the transom. I'm pretty sure its in the head, before the manifold bolts to the exhaust ports. I feel like something is supposed to go there, but I have no idea what. I have all the service manuals (thanks to yall) and I cant seem to find the hole on the factory pics. There was a homemade red RVT plug someone put in there, this is how I know its perfectly round, but not threaded. needless to say it came out after a few minutes of engine running. Does anybody know how to fix this, or what may go in the circular hole?
Any help is appreciated,
BenW

 

[achris]

Re: Exhaust leak before manifold

Ben,

Can you post photos?

Chris.......

 

[Thunderbird885cc]

Re: Exhaust leak before manifold

The 470 is a Mercrusier only design. Its a Mercrusier block with a Ford 460 head bolted to it. Perhaps the head has been changed and has an emissions port in it?

Perhaps you can get away with puting a frost plug in ? http://www.imperialinc.com/grp293.shtml they have a 1/2" cup style plugs

 

[Phylarch]

Re: Exhaust leak before manifold

Thanks Thunder,

That sounds like a solid answer. I dont have any pics, but will try to get some as soon as I get home.

 

[Bt Doctur]

Re: Exhaust leak before manifold

might be #11 in this link
http://www.marinepartsexpress.com/M...89/0B774252_UP/CYLINDER HEAD-ROCKER COVER.pdf

 

[Phylarch]

Re: Exhaust leak before manifold

Oh yeah, BT, thats exactly were it is, maybe a little more to the port side, but definitely in the head and not the manifold.
Thanks guys youve been a great help