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Jeep is an 84' CJ-8 with the 258ci motor. The existing cylinder head currently has 3 burnt exhaust valves (my excuse for the swap). The plan is to swap a 91' or newer 4.0L HO head onto the 258 block as well as run propane conv. I've been doing my research and have discovered that 81-87' blocks use 7/16 head bolts. The 4.0L uses a 1/2 bolt. I plan to use spacers/shims instead of tapping my block out. Where can these be found? Also who has the best deal on a reman. 4.0 head? Aside from sealing the h2o jackets, and a 4.0L header what am I overlooking? Let me know your thoughts.

-Erik

p.s. Anyone know how to get ahold of Clifford Performance? their site just brings up a search. www.cliffordperformance.com are they out of business?
 

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If you use the '87 to '90 head, it will have the same headbolts and combustion chamber size. The HO head has a smaller chamber which will pump up cmpression and start it pinging. The true flow difference between a mildly worked HO or Renix head are very small. The higher HP comes from the cam timing change in '91. They retarded the cam to lower the VE (volumetric efficiency) of the cylinders which also moves the power band to a higher RPM. (it's also part of why the HP gain over the earlier ones)
 

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I'm tired, so I'm going to cut and paste another post I did on another site...

I just finished this head swap and the details are pretty fresh in my mind.

What would you like to know?
Here are a few of the things I remember that frustrated me:
I used a wrangler 95 head.

7/16" head bolts (stock for my year) can be used but you need 1/2" adapters and I have some left over. Or you can drill and tap up to 1/2, but I don’t know about the next thing. I got them from summit I think they were for a Ford V-8.
ARP does not sell the head bolts that have the threaded extensions above the head giving you nothing to attach a fuel rail (if you have MPI)
That means you must buy at least 3 stock type head bolts at $25 a piece.
I talked to ARP and they laughed at me for being concerned about the torque and different stretch … after I told him that it was a 4500rpm motor at about 200 hp.

Not all valve covers are the same. They use different caps, breathers, pressure/vacuum attachments, and so I suggest you bring your valve cover with you to the dealer when buying those parts.

Not all rotors and caps are the same for MPI, so bring that with you too.

The Borla header for a 95 Wrangler hangs too low in my opinion. I had to make a p-trap to get back up over my skid plate, so check out the Gibson if it is CARB. (picture hopefully below)

The 4.0 head is taller then my 83 4.2 head.
The aluminum bracket that holds the idler pulley had to be ground down to make all the bolt holes line up. I used a Dremmel tool and took my time it turned out ok.

The Borla headers come off the head farther then the stock manifold, so my PS pump brackets had to be cut a lot!
Also the bolt that used to go to a welded nut on the back of that same plate must be changed to the front of that plate and ground to clear, and then the bolt had to be cut down.

Hmmm what else?

There are the items that are often talked about too like blocking the ports, spark plugs, gaskets, etc.

On the water ports, I have lots of those packing peanuts if you want some.
I used JB weld, but I have since read that is not the best option.
Before having the head decked I took the dremmel tool and chamfered the edges of the water ports, so that the epoxy would be trapped in place and also be hour-glassed around the metal. Not much, but the machinist thought I should, so I did.

If I didn’t cover it, then let me know.
 

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I made my own 1/2 x 7/16 spacers/sleevers for the head bolts. Just turned them on a lathe, worked like a charm. The sleeves are for alignment purposes only so you just need the two front and two back ones. If you can't make them yourself there's a company on the net that sells them. May have been Hesco but I don't remember for sure.
 

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Agree with most of what has been said. I have an '84 (different Jeep than the one in my sig) that I just did this to.

Used a Clearwater conversion head, second one I've done using them, they work great.

Built a new power steering bracket out of steel because I thought the aluminum one would be weak once I cut enough out of it to make it useable. I moved my power steering to the left about one inch by adding a strip of steel to the front plate and drilling it, then when I made the steel replacement bracket I adjusted it to fit.

Also used the Clifford spacers, they worked just fine as well.

Had a clearance problem with my MAT and the brake boster, so I moved it over to another port an inch or so away...that also works fine.

Used a Borla 17127 header that I got off eBay...it works real well too. Had an exhaust shop add a bell and a foot or so of extension to make the exhaust fit, no problem there either.

Tim Weaver's aricle on monsterslayer.com is great, tons of info there.
 

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i did this swap last year. i just made sure that my old bolts were centered in the hold with as close to equal spacing around them and carefully tightented them to the correct torque specs and sequence. i decided on this after talking to one of the tech links in the monsterslayer page. he said they would gladly sell the spacers but you didnt really need them.
 

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compression ratio

when you sway the 4.0 head what kind of compression ratio do you get
is it streetable with regular 87oct gas? are there cams available with more overlap to bleed off some compression????/?
thanks
i am just looking at doinf a 4.0 head on my 4.2
or just swapping a 4.0
thanks
andy
 

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I did the MPI kit before I did the 4.0 head conversion, and had pre-detonation problems with it set up that way. Though the 4.0 head increases compression, the shape of the cylinder head actually decreases pre-det (if the rest of your motor is in good shape...I know lotsa guys that have done these head conversions and ended up with a new short block as well because the oil getting past the rings will tip the octane balance and cause pinging).

I run premium in mine and it never, ever pings. It might with regular, I dunno, never tried it.

I would also read this thread before you do this conversion: 4.2L MPI Kit Pinging Problem.

Also, I am concerned about the center and tighten method used by Murfman. I was told that eventually, through expansion and contraction, the head would move around and eventually the head gasket would fail.
 

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carnuck said:
If you use the '87 to '90 head, it will have the same headbolts and combustion chamber size. The HO head has a smaller chamber which will pump up cmpression and start it pinging. The true flow difference between a mildly worked HO or Renix head are very small. The higher HP comes from the cam timing change in '91. They retarded the cam to lower the VE (volumetric efficiency) of the cylinders which also moves the power band to a higher RPM. (it's also part of why the HP gain over the earlier ones)
I CALL BULL SHIT! ...
And the hundreds of sucessful and satisfied conversion vetrans will agree.

Here is a link for those wanting check out Tim Weaver and I's colaborate effort first posted in 1999 on my MonsterSlayer.com/jeep site ... http://monsterslayer.com/jeep/40Head/40Head.htm

Here is the link to my main page at http://monsterslayer.com/jeep/Default.htm for those wanting to bookmark my related white sheets ...
"AMC 258 4.2L Engine, Head & Crank ID Chart"
"4.0L YJ Borla to CJ Chassis Modification Page"
"CJ Power Steering Bracket Modification for 4.0L Borla"
... concerning other 4.0L head conversion issues menitoned in this thread
plus these and other well reguarded tech articles ...
"CJ Gauge & Sender Diagnostics"
"CJ Hydraulic Clutch Conversion Page".
 
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