4.0 Head on 4.2 Block - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-05-2001, 12:32 AM
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4.0 Head on 4.2 Block

Sent in a question concerning the overlap of the 4.0 water-jackets on the 4.2 (258) block in December. I was (am)curious if the overlap is a variable. Is there some combination of head/block that eliminates or minimizes the overlap? As I mentioned before I've done the head swap on my 84 CJ7 and it's great. I epoxied the ports on the head and no problem to date. I know the 91 thru 94, 7120 head is the one to use. Will be doing a swap on my favorite idiot son-in-laws 86 in the near future. Any one got a suggestion? Must be someone out there with an answer. Come on guys, don't let me down!!

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post #2 of (permalink) Old 01-05-2001, 12:54 AM
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Re: 4.0 Head on 4.2 Block

I've tried to get some idea of problem casting years from the occasional feedback off the head swap tech page but could never pin down anyone who would provide casting numbers or production years of blocks that had a particularly narrow margin of seat area on that (manifold) side.
Just seal those 12 triangles up since it doesn't hurt anything.
It is added protection and lends piece of mind - then forget about it [img]/wwwthreads_images/icons/smile.gif[/img]
Most who didn't seal them got away with it. Some did not.
One (really pissed off) guy got wet!

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post #3 of (permalink) Old 01-05-2001, 04:04 AM
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post #4 of (permalink) Old 01-05-2001, 08:15 AM
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Re: 4.0 Head on 4.2 Block

My 87yj has an 86 block in it. We got a 92 4.0 head and put it on. When test fitting thehead the water jacket problem was pretty obvious. Mine still leaks, but not bad with the epoxy. The expoxy is not the way to go though...I'm going to clean out the epoxy this weekend and put in some .75" freeze plugs. Hopefully that will stop the leaking. I'm also going to enlarge the water jackets on the head that do match up with ones on the block to the same size as the ones they meet up with in the block. I'll let you know if it works after a week or so of driving.

4.2 w/<font color=blue>(4.0 head & MPI)</font color=blue>
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