Here's my question: aside from the mounting brackets between the WJ/TJ vs XJ/ZJ are there any differences, internally between their 4.0 I6 motors.

Here's my situation.
I got a 2000 XJ 4.0 4x4 which had low oil pressure for almost a year and a half before it actually kicked the bucket. During that time I decided when it does I will rebuild since it's turning 20 years old. I made the grave mistake of getting a fully rebuilt TJ motor. Now everything is brand new within that motor. It has not even been started. But I want to know if the Cam shaft, journal, journal bearings, pistons, rods, and lifters can be swapped into the old XJ block.

Granted I've already accepted I will have to have the XJ block machined before hand to make the pistons fit. However can the camshaft and journal still be used?

Thank you for any help.

So yeah, despite external differences between the motors throughout the years, all internals are the same.
Thanks for nothing and feel free to revive this in 6 years. I won't care or be a giant dingus about it.

Hey look at that, you figured it out on your own. Probably wasnt that hard to do.

Internals are actually different through the years. You can still mix and match stuff between the years but there are differences. So no, they are not the same. Glad I could be of help.

The question that arises is did the TJ motor have oversized pistons fitted, or was the XJ block good enough to take standard pistons without rebore ?

My thought is to exchange the TJ motor for an XJ motor, or sell it outright and rebuild the XJ you have. Why spend all that money trying to cobble something together? You may be sorry you even got started swapping parts. You're going to have to disassemble the TJ to get dimensions of the pistons anyway, so why not sell it as whole to someone who needs it. IDK if I'd want to buy a rebuilt motor that's been taken apart by someone I don't know. Is it possible to exchange it from where you bought it?

Did you use the 90 degree oil filter adapter, or just run it with the filter straight into the block?

If only you had gotten the 99 and earlier TJ motor!!

I actually haven't thought of that because I've been so wrapped up in getting my dimensions and parts right.

The XJ motor has the 90° attachment. The TJ oil filter screws right on. Which is better in your experience?

It would be nice to get a plug and play motor so to speak. But I got a sweet deal. I paid 600 for the motor with brand new everything, the head was refurbished with new valves, rods, timing chain, pistons, camshaft, journal, and bearings (which wont be reused)
The deal also included accessories like water pump, alternator, ac compressor.

So with that being said. I'm not getting rid of it as it would cost more to acquire all parts individually/separately. It took me almost 3 months to beat the dudes price down from 1,200 to 600. It was practically a day time robbery.

I'd like to know this as well. But I work 7 days a week so making time is my biggest dilemma. As we speak both blocks are basically ready to be gutted but I'm having difficulty finding the right tool to remove the harmonic balancers. This is my 2nd weekend straight of renting the wrong tool. Once I pull the journal and pop the pistons out I'll have my answer regarding bore size.

This will not be revived in 6 years because we will all remember you're a d-bag and expected answers to questions that are extremely technical in nature that only a highly experienced technician can answer who has actually even taken the time to measure internal parts down to the 0.001" when you could have just looked up the parts you needed, gotten the part number, then checked to see if its the same part number from the donor motor.