thinking about going to a 4.0 head - JeepForum.com

 
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post #1 of 10 Old 01-02-2013, 10:06 AM Thread Starter
akagrifty
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thinking about going to a 4.0 head

ok i have been looking through page after page for some info but i can't find any useful info. I am getting oil out the exhaust when i let the jeep idle for about 5 min then press on the gas. I am almost positive it is my head. I don't want to rebuild the old head i am going to just replace it. I have heard that a 4.0 head is a lot better on the 4.2 motors. Have I heard right? Do I have to replace the intake with fuel injection? I guess basically I am looking for some good info before i jump into this thing and find out that there is way more involved then just swapping out heads.

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post #2 of 10 Old 01-02-2013, 10:18 AM
hypernoodle
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It's as simple as just swapping the head. The old intake manifold should bolt right up.
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post #3 of 10 Old 01-02-2013, 10:24 AM
stroker90
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In my research a few years ago when I was thinking of doing this I thought you need to fill in some of the water ports in the head since they don't match up
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post #4 of 10 Old 01-02-2013, 04:19 PM
hypernoodle
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There are water jacket ports on the head that don't match up to the 4.0 block either.

Just use a 4.0 head gasket and it'll seal up nicely.
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post #5 of 10 Old 01-02-2013, 05:23 PM
roadyrob
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if you search for "4.0 head swap" you will find plenty of info. there are waterjacket holes that need to be plugged. the 4.2 intake will work but its not a perfect fit. while its not as simple as just bolting it on and go its not a hard mod. to get full potential out of it installing fuel injection AND a fuel injection cam is the best way to go.
if your going to stay with a carb I'd spend some time on the 4.2 head cleaning up the casting and port matching it.

Do everything with a positive attitude, it won't always work but you'll piss enough people off to make it worthwhile.

the voices aren't real but they sure have good ideas.
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post #6 of 10 Old 01-02-2013, 09:25 PM
skyj
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Quote:
Originally Posted by hypernoodle View Post
There are water jacket ports on the head that don't match up to the 4.0 block either.

Just use a 4.0 head gasket and it'll seal up nicely.
I'm sorry but your wrong! The 4.0 head is slightly wider than your 4.2 block thus the water jackets will overhang causing a massive leak.
I have done this swap and its a good mod. What you need to do is fill the water jackets in the 4.0 head with a high temp epoxy ie: quik steel, or JB weld. I filled the jackets with dissolving foam peanuts then covered over with quik steel epoxy. Then I had the head milled flat. If you want to run your carb you will need to make slight adjustments to your intake and power steering pump bracket. It's definaltely not a bolt on and go but its very simple for your average backyard mechanic. Good luck I would be glad to help you with anymore questions if you need.

build thread: http://www.jeepforum.com/forum/f22/skyj-eccentric-build-1467426/ '90 YJ 5.2 magnum MPI, AX15, NP231 SYE, Dana 30 4.56 open/ 8.8 4.56 detriot locker. 1" shackles
2" BL, 4" stretch all on saggy waggy springs.
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post #7 of 10 Old 01-10-2013, 07:09 PM Thread Starter
akagrifty
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Ok so I am going to do this mod. I am just not sure now if I want to switch over to the efi when I do the mod. Will I have to take the trans out to do it? Does anyone have a link to a thread with someone who has done this? Also is there any reason why I couldn't find an old Cherokee an steal all the parts I need out of that? 1 last question for now should I use the push rods from my 4.2 or should I get the push rods from a 4.0?
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post #8 of 10 Old 01-10-2013, 08:59 PM
skyj
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Quote:
Originally Posted by akagrifty View Post
Ok so I am going to do this mod. I am just not sure now if I want to switch over to the efi when I do the mod. Will I have to take the trans out to do it? Does anyone have a link to a thread with someone who has done this? Also is there any reason why I couldn't find an old Cherokee an steal all the parts I need out of that? 1 last question for now should I use the push rods from my 4.2 or should I get the push rods from a 4.0?
You will have to drop the trans to install a 4.0 flywheel if you go with the fuel injection, or you can buy the hesco cps run off the harmonic balancer ( 300 bones$$). If you stay carb you wont need to. I never did a writeup when I did mine I used a thread on offroad.com. I robbed all my parts off of a'93 Cherokee, in my opinion that is the best year its got the the good head. It's also pre obd11. If I remember correctly I think I used my 4.2 pushrods.

**edit here is the article I used.
http://offroad-review.com/new/index.php?page=68
And if you decide to go with fuel injection read this.
http://www.jeepforum.com/forum/f12/4...build-1114875/

build thread: http://www.jeepforum.com/forum/f22/skyj-eccentric-build-1467426/ '90 YJ 5.2 magnum MPI, AX15, NP231 SYE, Dana 30 4.56 open/ 8.8 4.56 detriot locker. 1" shackles
2" BL, 4" stretch all on saggy waggy springs.
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post #9 of 10 Old 04-02-2013, 04:40 PM Thread Starter
akagrifty
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I haven't done this mod yet just because after doing all the research i found that you can't swap out the flywheel because 4.0 engines are internally balanced and 4.2 engines are balanced by the flywheel. If you swap out the 4.2 flywheel for the 4.0 flywheel you will destroy the engine.
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post #10 of 10 Old 04-02-2013, 07:36 PM
blown50
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Quote:
Originally Posted by akagrifty
I haven't done this mod yet just because after doing all the research i found that you can't swap out the flywheel because 4.0 engines are internally balanced and 4.2 engines are balanced by the flywheel. If you swap out the 4.2 flywheel for the 4.0 flywheel you will destroy the engine.
Don't think this is correct! Only differnce is the ring for the crank sensor.
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