Bought my YJ toy a couple of weeks ago. Sounded like the exhaust was leaking at the manifold - replaced two broken studs and the gasket (it had just the intake gasket, new gasket covered both intake and exhaust). On to the next noise...
Took it to a fellow Jeep enthusiast's auto repair business, and he used a stethoscope to determine the source. It's a consistant knocking noise at the front of the engine. He believes that the timing chain has stretched and is slapping around inside of the cover. About 3-4 hours to replace, plus parts. Total around $300.
I thought about doing it myself, but decided to pay them to do it. Do you think the estimate is reasonable? It sounds like it is to me. I know that the oil pan will have to be dropped in order to change the tensioner. It's labor-intensive work. I'd rather enjoy my weekend than screw with it.
Also found that the passenger-front u-joint is bad, and the steering box seal is leaking.
Jeep has 139,000 miles on it, and is otherwise in pretty good condition for the age.
Michelle in Northern Illinois