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Unread 06-30-2013, 02:11 PM   #1
DaemonForce
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4.2 -> 4.0 possible?

I finally decided to give this forum a shot since every hosting provider in existence seems to go boom right along with my car so I'm wondering who here can help me figure this out. I'm a classic AMC enthusiast and though I've been relying on the inline 6 engine for the past 5 years, I'm open to using a 4 or 8 but those options aren't available. I would like to swap a recently blown 258 for whatever I can pull from the boneyard.

Here's what I know:
Not all 4.0's are equal. Some have a crack-prone Renix head or a nice Chrysler head...I have a spare Chrysler head with the water jackets filled.
Not all pans are equal. The 4.0 pan is a nightmare. I need to reuse the 258 pan or face clearance issues with the Eagle crossmember.
The bore is bigger but so is the 258 crank. I have a spare I intend to use to make a 282 stroker.
I prefer carbs but the 4.0 standard is fuel injection. I need help understanding this.
Because of FI electronics, I may have to change the entire drivetrain.

Issues:
I don't have an isolated place to work on this. I have an open yard in SW WA and I don't have anyone to help me with the lifting or overhaul work. This means I'm on my own. I've been taking care of an 83 year old grandpa for the past two years so that's where the majority of my attention has gone. I risk being kicked out within a few months over his health issues and that means I need to get this car running again or I will lose it along with any chance at a job for many years. Any help would be appreciated.

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Unread 07-01-2013, 06:24 PM   #2
cruiser54
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The head cracking issue is exactly the opposite. Only the latest CHRYSLER heads were prone to cracking, beginning in 2000. That's the 0331 head.
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If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 07-01-2013, 10:48 PM   #3
DaemonForce
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No I pulled the 7120 head from a 1990 Cherokee Pioneer. Also, read that again. It was the most bizarre thing I've ever pulled from the junkyard. Of all the ones available to pull, I chose THAT one. It doesn't make sense to me either.

Anyway, I'm wondering what all I need to worry about when doing this. Will it fit my engine compartment, what injectors to use, how to reuse my torqueflite transmission, what flexplate to use when bolting it up, what starter to use...All that fun stuff.
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Unread 07-02-2013, 06:05 AM   #4
cruiser54
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I'm betting the 90 had an engine swap done. 2686 should be on a Renix 1990 XJ. 7120 was the first generation HO head.
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 07-02-2013, 06:52 PM   #5
DaemonForce
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That's what I figured when I saw it. I had no way of identifying the injection system and was told to avoid Renix so I left the intake alone. What does the ideal intake look like?
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Unread 07-02-2013, 07:36 PM   #6
cruiser54
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There is no ideal intake IMHO. How many bolts hold the throttle body on?
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Quote:
Originally Posted by chris87xj View Post
If you own a Renix Jeep, you'll want to check this out. >

An index to over 25 write-ups can be found in Post #1.

Cruiser's Mostly Renix Tips
My Jeep Technical Photos

http://www.cherokeeforum.com/g/album/1725214
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Unread 07-02-2013, 07:45 PM   #7
zx150
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I'm in the process of doing the same thing with an Eagle, a J10 and sometime soon a DJ5. It can be done.

The first gen HO injection is probably what I'll go with along with a 7120 head.
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