Just got done putting a new engine in a '92 Laredo. Same thing wrong with piston in the original. Made noise forever but kept running. I did everthing to that engine to try to stop it from making noise including new rockers on the bad cylinder, new cam, new lifters, cleaned all the pushrods. Finally a small part of the piston lifted enough to hit the head and it really started to pound. That was it for it. It made noise when I bought it at the start of our sons college and lasted through his masters before it let loose. I usually associate the 4.0 as a good engine as our other '92 went 317,000 before we just burned out on drivng it and gave it to one of our daughters. It still got 18.2 mpg, same as new, and never used any oil. I changed the oil in it 109 times, and the rear seal every 100,000 to 120,000 miles because of leaks. If I remember correctly it was number four cylinder that had the bad piston.
