Cylinder head cracked

[brielly]

I was about to replace my exhaust manifold when I found that the cylinder head was cracked right where the end bolt holds on the manifold. I have an old 258 head with low miles that I pulled years ago and a 4.0 head with about 160K on it. I'm leaning toward the 4.0 since I already have the mopar efi but was wondering what everyone would recommend as to reconditioning it. I'm not sure of the miles on the bottom end of my engine (was supposedly rebuilt). Iv'e heard its not a great idea to put a freshly rebuilt head on an engine with high miles. I guess I'll do a compression check first but what is the minimum work I should have done to the head?

[tgreese]

JMO - inspect the head and test for flatness with a long machinist's rule. There is a spec in the TSM. This is a common problem with long heads like these. Remove the valves and look at the condition of the seats and valve margins. The exhaust valves take the most abuse, so any pitting is likely cause for rejection. Look for cracks with a magnifying glass and an intense light. If everything looks ok, put it together and hope for the best. If the heads came from a running engine, they should be ok for a while. No guarantee - there is always a risk when you try to cut costs this way. There used to be new 4.0L HO heads for sale at ca $500, but a quick look did not find them any more. Maybe they are still available. If you go with the 4.0L head, it hardly seems worth it to spend say $350 to refurbish it if a new head is available for $500. Make sure you aren't using one of the 4.0L HO heads that are prone to cracking. There are specific casting numbers that are bad.

[candymancan]

The 4.0 that cracks are the 99 and up the zj 98 and under are ok

[brielly]

I'm actually leaning towards the 4.2 head now. The one I have now is in better shape than the 4.0 and it will cost less being that i already have 4.2 exhaust manifold. I'm going to clean up the 4.2 head and test it to make sure the valves are not leaking. I'll also change the stem seals. I did the 4.0 head swap on another jeep years ago and the performance increase wasnt as advertised. I'm also not a big fan of sealing water jackets with epoxy. Hopefully all will be fine. Definitely going to check for flatness as well.

[tgreese]

Sounds like a plan. Good luck!