1991 XJ Engine Replacement?

I was pulling my snowmobiles up Monte Cristo Canyon here in Utah and about halfway up the mountain my Jeep choked out for a couple of seconds and then took off again like nothing had happened. When I got to the top I noticed that there was a knocking noise coming from the bottom end below cylinder #6. I took it in to a local mechanic and he told me that either my rod or cylinder is cracked and I will need a new engine. I have driven it around a little bit and the knocking is getting louder. Do I really need a new engine or can I rebuild it? I have priced out a rebuilt short and long block and they run from $900 to $1200 on the cheap end. Is it worth my time and money to rebuild it or would I be better off buying the long block? Also if I wanted to go with a used engine what years would fit in my 1991 XJ?
Thanks.

Not a way to really recommend anything, untill you drop the oil pan and actually see whats wrong. You might have done anything from spun a rod bearing to broken a piston. Keep on driving it and you will just add a towing bill. Junkyard motors are a gamble. The lower ends or short blocks are pretty much any year cept for maybe a couple of mounting holes. If you reuse your head it should be pretty straight forward. How long you plan on keeping the jeep also comes into play. If you are going to keep it for another 3 or so years you can go the expensive option of say a Jasper rebuilt that comes with a good warranty that covers labor too, thats about $3000 or so. That option though is a COMPLETE engine that drops in, move some parts over and plug it in.

When I crashed my old XJ ('91) to the point that there wasn't enough sheet metal or parts left for it to still be road legal, the engine had been rebuilt before I had acquired it. I picked up my current XJ ('91 as well) for 350$ because it had an engine knock just like yours. I opted to swap the engines, and it ran me about 1200, because I had no clue as to how to go about it myself, so if you can get a rebuild done for around 900, I'd probably opt for that. I don't think you'll need a new engine, because I could have had mine rebuilt with the same knock you have, but I couldn't find anyone that cheap to do it (and hey, I got to keep the heart of my old girl anyway).

Opportunity knocks.
Rebuild your 4.0 into a 4.6 stroker. You'll love it.
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