4.0 head 4.2 block

Went to buy a motor I saw on craigslist. Advertised as a jeep straight six. Well on closer inspection its a 1992-1997 4.0 head with a 4.2 block. I know guys do the head swap in yj's and cj's but I am going to need to put a motor in my 1992 xj here pretty soon. Is it worth doing the 4.2 swap or would I be giving up too much?

joejeep92 said:

Went to buy a motor I saw on craigslist. Advertised as a jeep straight six. Well on closer inspection its a 1992-1997 4.0 head with a 4.2 block. I know guys do the head swap in yj's and cj's but I am going to need to put a motor in my 1992 xj here pretty soon. Is it worth doing the 4.2 swap or would I be giving up too much?

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What would u be giving up? Sounds like its a stoker..

Not sure about swap-ability into the XJ. It can be done, but it's not going to be a straight bolt-in.
Unless you're dumping the XJ ECU/FI setup:
I don't think the 4.2 flywheel/flexplate is inter-changeable with the 4.0, and you need the tone ring from the 4.0 to give a signal to the CPS.
Depending on the year, the 4.2 has a longer crank snout then the 4.0, and would require modification to fit the 4.0 harmonic balancer and accessory drive.

It's basically a 4.2 stroker. It'll work, the parts your computer cares about are in the head, but you may find that you want to run a slightly larger injector to keep it from running lean on startup.

The way I figure I can run a 4.0 acessory setup. Alternator, power steering, etc. Motor mounts should be the same and putting in a 92-97 head coupled with correct manifold makes it a straight swap into my 1992 4.0/AX15 in my mind.

I am sure the 4.0 flywheel will work just fine as many of us have 4.2 cranks in 4.0s! The CPS is mounted to the bellhouseing as well so no problem there. You might run into other things that may or may not bolt onto the block.

Yeah I have a day off wednesday so I was planning on swapping accessories onto it until I find one that doesn't work...