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Discussion Starter · #1 ·
I would like to know if the water jackets on the exhaust ports side of a 4.0 head need to be welded up when doing the conversion onto a 4.2? I dropped the head off at the shop and he said that he didn't weld on cast iron and that it would be expensive. I don't want to do it unless I have to.

 
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Discussion Starter · #2 ·
I've heard of guys relying on the head gasket to seal it, but personally, I wouldn't do it. At the very least, I'd use JB Weld to seal it off, and then have it milled as usual. The folks at JB say once it's fully cured, it can be machined or even threaded. I remember hearing about another similar product that may even be better... I think it was what John used to fill in his CJ dash to fit smaller than stock gauges. Check out John's Jeep Page it's an invaluable tool for building up a 4.2 and Tim has an excellent write up of the 4.0 head converstion there too that may answer your questions better. Let us know how it goes. Happy Jeepin'!

-Spyder
 

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I have installed the 4.0 head and All I did was use the 4.2 head gasket. 18 months and no leaks yet.


Enjoying Montana's Big Sky (& rocks & rivers & mountians etc, You get the picture.)
 

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It is recommended these edge ports be welded or expoxied over.
I don't know if Devcon Plastic Steel epoxy will work as well as the old time block-proven JB Weld epoxy but I expect it should. Devcon makes excellent products and are one of the world leaders in epoxy adhesives. It could easily be filed flush to the head's deck with a large bastard mill file. It is really good stuff and strong as it has visable metal flakes that helps the integrity of the mass considerably.

I DO know that both Clifford and Hesco both weld these jacket ports closed and then mill the decks flush on their custom 4.0 heads intended for 258 blocks.
 
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