engine rebuild
 

I have a 1988 jeep cherokee 4.0 stright 6. Bottom end making lots of noise. Is it possible to rebuild the bottom end from pistons down without removing the engine?

Honestly you would probably be better off just taking the engine out and rebuilding the whole thing considering your working on it. I havent had to do it myself but it would probably be worth it in the end.

I don't believe the pan will come down far enough to get to rod & main bearing caps off. Even then sliding the bearing in the upper side of the crank would not be fun.

Just pull the motor, and rebuild it on a stand.
Your sanity will thank you.