Our 90XJ 4.0 is clacking when started and when revrd up. Someone said valves, someone else said rod and crankcase bearings which I may as well do a rebuild. My ? is can one replace the rod and crankcase bearings without pulling the engine?

My ? is can one replace the rod and crankcase bearings without pulling the engine?
Yes, it can be done. It would probably be easier just to pull the mess and work on it while its out.

Another alternative is a used engine. I bought a used 4.0 off e-bay for $500 shipped. It had 50k when I got it and ran awesome.

If its the valves (lifters getting old, cam wearing down) A valve job with a new cam/lifters, If you do the work yourself cost $400 to $1000 depending on your taste.

The first thing is to find where the noise is coming from. Use a bar when you start the motor, place one end of the bar on the valve cover the other end on your ear. Do you hear the noise move the bar to the lower part of the motor. The noise will transmit up through the bar.

Pickin pull Junk yard sell motors $250 and up. Nothing wrong with a used motor. But the thing is, are you buying someone elses problem? I have a used motor in my CJ Bought it from a guy who was doing a V6 FI, Paid $50 for it and lovin it. (#3 cly blowin oil in the old motor)

When you start the motor and the noise goes away: Thats just a sign of old age (like the old bones crackin when you get out of bed in the morning) The oil filling the gaps. I have run motors 100,000 miles this way with no problem.

My :2:

I bought a used 258 for my sons YJ on E-Bay for $256.00 and we did a road trip to pick it up.This way he can still drive his Jeep while we rebuild the other engine and do the 4.0 head swap.