4.0 Block Crack - JeepForum.com
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post #1 of 8 Old 05-06-2021, 12:52 PM Thread Starter
Neuner-9R
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4.0 Block Crack

I have a '98 4.0 in my CJ7 and why I posted on this side of the forum. Hoping the experts over here might help identify whether or not my block is cracked?

In my research of this engine before the swap, I thought only the '02-03s were prone to cracking?

It's right underneath the header so it's difficult to view and get a decent pic. I only have a drop or two of oil after each drive so I don't think it's anything major. Plus I have another leak in the bottom pan seal.

It's been like this for quite a while so I don't think it's getting worse. I had to do a bunch of other work before looking into this.

In the photos, I think there are potentially two cracks right on or above the casting number? Would this be a minor or major repair?

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post #2 of 8 Old 05-06-2021, 12:57 PM
Kaptainkid1
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Quote:
Originally Posted by Neuner-9R View Post
I have a '98 4.0 in my CJ7 and why I posted on this side of the forum. Hoping the experts over here might help identify whether or not my block is cracked?

In my research of this engine before the swap, I thought only the '02-03s were prone to cracking?

It's right underneath the header so it's difficult to view and get a decent pic. I only have a drop or two of oil after each drive so I don't think it's anything major. Plus I have another leak in the bottom pan seal.

It's been like this for quite a while so I don't think it's getting worse. I had to do a bunch of other work before looking into this.

In the photos, I think there are potentially two cracks right on or above the casting number? Would this be a minor or major repair?
Uses some purple cleaner and clean, decrease the area and see if the drops come back. Also it looks like oil drips to me. Could be a valve cover gasket leak too.

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post #3 of 8 Old 05-06-2021, 01:02 PM Thread Starter
Neuner-9R
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No leaks around the valve cover gasket.
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post #4 of 8 Old 05-06-2021, 01:34 PM
Wyo
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Certainly looks like a crack to me but here you can be certain:
https://www.amazon.com/dye-penetrant...+penetrant+kit
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post #5 of 8 Old 05-06-2021, 01:51 PM
Mousejockey
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Spray it with degreaser, I like superclean, then power wash it
then look at it
Looks to me like oil is running down the support bracket then to the block
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post #6 of 8 Old 05-06-2021, 06:31 PM
jkp
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I'm not aware of any block cracking issues, it was the 0331 heads that were prone to cracking.
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post #7 of 8 Old 05-07-2021, 02:14 AM
Kaptainkid1
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Quote:
Originally Posted by Neuner-9R View Post
No leaks around the valve cover gasket.
When you install the engine did you use Anti-seize on the exhaust manifold bolts?
It looks more like grease or a dirty engine block. As mentioned before clean it and Start over on a fresh clean block. Check for leaks after that. That's my bet on the problem.

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post #8 of 8 Old 05-08-2021, 11:11 AM
Jeepsr4me
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There are a lot of part lines in the block. When the block was made the sand mold allowed some of the metal to fill in the lines of the area where the mold was put together.,


I have seen a lot of engine blocks and none have cracked in the areas you showing,.


Clean it real good, pressure wash works just fine Or brake cleaner in that area and get all oil off and see if it returns.
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