Which 4.0 Head for 4.2 swap - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 12-27-2000, 01:46 PM
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Which 4.0 Head for 4.2 swap


i'm interested in doing the 4.0 head to 4.2 short block swap. read the tim weaver web site and understand that any 4.0 head from 91 to 95 will work (can the new 4.0 Heads from the TJ's work as well??). was wondering if there was a specific year that people had the most luck mating the 4.2 block with 4.0 head - ie where the water jackets overlap the least. while reading some articles about the conversion, i have come across some stories about either there are overlaps in the water jackets or there are some serious issues with valve push rods being too long causing the valves hitting the top of the cylinders at exhaust stroke (has anyone had that happen to them because of the 4.2's supposed longer stroke than the 4.0?). just wanted to see if there was a specific year 4.0 head where the swap would lead to the least "issues".

btw, i'm swapping to a '83 258 short block in my CJ7. i'm not rebuilding the short block; just swapping in the 4.0 head.


83 CJ7 258/T5
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post #2 of (permalink) Old 12-27-2000, 02:02 PM
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Re: Which 4.0 Head for 4.2 swap

I can't tell you about the '97 and newer 4.0s, but the casting number is 7120. Any 7120 head should be identicle as to overlap. I haven't heard of the problems with long push rods....mine worked fine from my '82 258 block.

You will need to either tap 1/2" holes in your block or use insert washers to line up the head using 7/16" bolts. Tim Weaver's article references Clifford as a source, but I was only able to find them through ARP, they are called Insert Washers. If I remember, the ID is 7/16" and the OD is .506. I only used two of these at opposite corners to get it lined up. The 7/16" head bolts from Mopar are $20 a piece. That alone may justify having the block tapped for 1/2" bolts (Tim's article says the whole set of 1/2" bolts is only $20).

Let me know if you have any other questions.

258 4.0 Head/MPI,NV4500,D300,4.10's,HS9500
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post #3 of (permalink) Old 12-27-2000, 07:08 PM
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Re: Which 4.0 Head for 4.2 swap

Hey Jack,
Im sorry I cant give you a good answer on the head issue. I have been kicking the idea around for some time but it just hasnt happened yet.
Anyway....... I see that you are running a howell EFI setup along with a GM HEI?
I have the GM HEI on my 89 4.2 and its great but I am also getting ready to order the Howell EFI set up.Can you tell me if there is anything special I need to know about it as far as the HEI goes??? Any special hookups or does it just bolt up?Any thing I have seen on it says it has to be used with the factory ignition system. Is there any advantages to ordering it through Howell directly or maybee from Four Wheel Drive Hardware,Quadratech or Rosser??
Thanks for any advise you can give!!!.......Herbie

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post #4 of (permalink) Old 12-27-2000, 08:21 PM
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HEI with Howell EFI Info

hi herbie,

the howell kit was a direct bolt on. since i bypassed the computer when i installed the HEI, i didn't need to perform that part of the Howell installation. the howell kit doesn't control timing so nothing needs to be modified as far as the distributor goes. only need to tap into the Tach signal out of the HEI for the computer.

ordering from howell i think is a bit cheaper which is why i did it.

hope that helps...


83 CJ7 258/T5
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