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Unread 12-22-2012, 08:13 PM   #1
94beachxj
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The best 4.0 L Cylinder head made?

After some research I have concluded the 1991-95......#7120 casting was the best for these Cherokee engines.
My ATK replacement engine was from a AMC 92-95 block.
I guess that puts me in the better of the mix?
What I have found on the other side is the 1999-04......#0331 casting was the worst casting, hence the over heating and cracked heads.
The # 2 cylinder area had weakness to the best of my knowledge.
Whats your thoughts on this?

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Unread 12-22-2012, 09:17 PM   #2
dmill89
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Quote:
Originally Posted by 94beachxj View Post
After some research I have concluded the 1991-95......#7120 casting was the best for these Cherokee engines.
My ATK replacement engine was from a AMC 92-95 block.
I guess that puts me in the better of the mix?
What I have found on the other side is the 1999-04......#0331 casting was the worst casting, hence the over heating and cracked heads.
The # 2 cylinder area had weakness to the best of my knowledge.
Whats your thoughts on this?
#7120 is generally considered the best. The #0331 from 2000-01 is generally considered the worst (very few 99s have the #0331 head, only those from the very end of the model year with coil packs have it). From 02+ the #0331 head problem was fixed for the most part, the corrected heads have TUPY stamped in the center.

The weakness in #0331 heads is generally between #3 and #4 cylinders. That being said #0331 is not absolutely terrible, they usually only crack if overheated. If you bought a 2000-01 new, maintained the cooling system properly, and never overheated it the odds of a cracked head are very slim, however if you buy one used you don't know the history and whether or not it has ever been overheated in the past, so there is always a risk of a cracked head on a used 2000-01.
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Unread 12-22-2012, 09:34 PM   #3
CJ7-Tim
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I agree with dmill89. The 0630 and the 7120 heads are considered the best performing and would be fine for any Jeep 4.0L. Actual cracked 0331 heads are very many fewer than the number of threads on various forums about them cracking. IMO nearly all cracked 0331 heads are the results of abuse through neglected cooling system maintenance.
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Unread 12-23-2012, 07:06 AM   #4
94beachxj
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Quote:
Originally Posted by CJ7-Tim View Post
I agree with dmill89. The 0630 and the 7120 heads are considered the best performing and would be fine for any Jeep 4.0L. Actual cracked 0331 heads are very many fewer than the number of threads on various forums about them cracking. IMO nearly all cracked 0331 heads are the results of abuse through neglected cooling system maintenance.
So true!
I use the "green stuff" and keep it fresh ! I made a thread a while back on how I rotate the new coolant in the system a little at a time. I will never need to flush a coolant system again using this method.
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Unread 12-23-2012, 09:41 AM   #5
mschi772
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Quote:
Originally Posted by dmill89 View Post
The #0331 from 2000-01 is generally considered the worst
Wrong. The 87-90 head, whatever number it is (686?), is the worst.

Furthermore, a head (or any other part for that matter) is only as good as the other parts around it. These parts all work in concert with each other and just swapping a head won't do much for you if you're not using a complimentary cam/intake/exhaust. The same can be said to all the people who think slapping a 99+ intake on an older engine will actually do something without a head/cam/exhaust to support it.

If you're building a custom 4.0 (or stroker) with all sorts of fancy parts, porting, polishing, the 7120 is the head to work with, but if you're just in need of a new head for your workhorse, it won't really make much of a difference.

0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.
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Unread 11-05-2013, 07:48 AM   #6
94beachxj
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Quote:
Originally Posted by mschi772 View Post
Wrong. The 87-90 head, whatever number it is (686?), is the worst.

0331 cracking issues? Way overexposed. The problem is real, but it is seriously exaggerated by the fact that people will log onto the web to say when theirs is cracked, but will never make posts advertising when there's HASN'T. There are a ton of 0331 heads out there that are just fine. Real problem, so always keep an eye on it, but just because you may have a 0331 doesn't mean you're fated for failure like people on the internet would have you believe.
I agree to a point. But if you change the coolant once a year, the green stuff will be your friend! The 4.0 runs hot with lots of pressure! One way to save that hot block.................be cool
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