checked out the website. seems like a great place to buy parts.

 

If I wanted to swap an entire engine, not just a head, what would be compatible. I have a 1991 XJ. I found a local guy on craigslist offering a 2001 4.0 with 91k miles on it, and was wondering if that would work in my Jeep. I'm assuming I'd probably have to swap the coil on plug for the distributor and swap a few other sensors over.

 

If you're going to swap out the short block (engine less cylinder head,) any year 1987-2007 should work.

For the long block (engine and cylinder head, no sheetmetal, bolt-ons, or brackets,) you want to try to stay withing 1991-1995 for your 1991. That will let you keep the 7120 cylinder head you already have. You can go a step farther to include the 0630 head - those two cylinder heads cover you to 1991-1999 (XJ) 1991-1998 (YJ/TJ/ZJ) Going to the 0331 head will likely get you a performance drop, and the 1999-2001 0331 heads are the heads that get you into the "0331 club" of cracked cylinder heads anyhow.

However, if you swap in a lock block with the 0331 head, know that all you really end up having to do is swapping the intake and bracketry off of your 7120 head (to use the same accessories,) and swapping out the oil pump drive/cam sync sensor for the distributor off of your 1991 engine.

EDIT - if you do this, I don't suppose you're anywhere near the SF Bay Area, are you? I've been looking for a 7120 head for research purposes - and I don't care if it's cracked or warped!

 

Thanks, I'll keep all that in mind when I start looking for an engine. No, I'm not in the Bay area, I'm near the opposite coast, actually, in VA.

 

That 2001 4.0 I found is still available, and I had one more question for it. Since the 2001 heads are prone to crack, I'm guessing it would make sense to hold on to the head from my old motor just in case. Or would I be better off just swapping the heads right off the bat, and not even bothering with the head from the 2001 engine.