I have a 91 yj with a 2.5L just like yours - yes it has a chain not a belt.
The noise clatter you reference, I assume is the same as all 4 cyl jeeps have. Many reference it as sounding like a diesel engine. Nothing actually wrong with it, it just makes that noise right?
This is caused by many problems, first of which is a MAJOR design flaw by Jeep. The problem is that jeep in their infinate wisdom decided to put the cam at the bottom / middle of the engine, and the rockers at the top of the engine. The oil pump has a terrible time getting enough pressure inside the engine design to keep everything properly lubed up to keep it quiet for a long period of time. (Try reving the engine to about 1500 rpm. Does it sound quieter all of a sudden. Let me guess, the oil pressure gauge also went up when you did this? Then your problem is oil to the rockers in the top of the engine.)
now - the thing is. Because of the design flaw, the engine doesn't properly lubricate like it should, and thus parts break down more frequently than they should. (If you can find one, and I haven't, you can try putting in a high volume (not high pressure) oil pump when making the other repairs as this will assist in future lubrication issues)
Your problem could be:
all of the above
Almost 90% of mechanics out there hear the noise and automatically assume the worst, that the engine must have major problems with it. I went to 3 locally and all 3 had different opinions about it - none of them were correct in my case - but it's just a lack of proper lubrication. Go ahead and take out the lifters yourself and see for yourself! Measure them up and verify with specs. Based on only 70K miles and as you said well maintained. My gut says the specs are within limits.
To properly diagnose it though, without knowing everything yourself would be difficult, and even more difficult to explain in this forum.
Try to envision the oil being forced up to the top of the engine through a tube about as wide as a pen without ink in it, now this happens in 8 different tubes. If one of those tubes gets partially plugged with old oil, or debris, then that reduces the amount of oil getting to the top, and making the noise even louder.
As for the guy telling you it's the timing chain - yeah it could be. If it was, the noise would be loud all the time, and probably louder with higher rpms. Add to this, the vehicle would be sluggish and not quite showing the same amount of power it should or what you were used to. Does this fit? If so, the timing kit should run about $80 for parts and the guy will probably charge an arm or first born for labor. The total job should take about 2 hrs or less, as it's pull off and put on type of set up. Then aligning the timing is simple too because jeep was smart enough to put alignment marks on the cogs the chain wraps around. (This I wouldn't recommend you do yourself unless you did know what you were doing though)
You want more. I can give you a ton of more details about the insides and outsides of this engine as I tore mine apart in my garage just a few months ago searching for answers to the diesel sound. Sucked, but. Happy I learned a whole lot more about it as a result too.
Sunday, June 8th, 2008 AT 4:40 PM