For the smart guys!
'92 Wrangler with 2.5L and AX-5. Its got 170,000 miles, but the motor ran like a watch. A year ago, a family member whom shall go unnamed, unwittingly drove away with it while the oil pressure sensor was uninstalled, waiting for replacement. The results were predictable, it made it about 3 miles, 5-10 minutes, before it stopped running. Once towed back to the house, the current knocking sound introduced itself upon restart. BTW, the video may feature the knocking slightly more strongly than it sounds in true life.
Assuming the bottom end to be wiped, I dropped the pan, and replaced the main and rod bearings, with a standard size set. Surprisingly, though some of the bearing were worse than other, and the main thrust bearing worst of all, the crank journals checked out pretty good, both on the micrometer, and using plastigage. Engine compression checks out good, with a 2.5% variation centered on 115 psi (one compression stroke, throttle open, all plugs out). Oil pressure holds 20 psi when hot. I have run it with the valve cover off, all actuation looks good, and was unable to damp or affect the sound by applying pressure on any of the rockers. Engine idles steady at ~700 rpm, at a steady 17.5 in. vacuum reading. Spark plugs look good, and the engine still runs smoothly, with about the same power as before. When I had the pan off for the bearings, I could not see anything obviously amiss with the rods/pistons/wrist pins (admittedly tough to see, but nothing clearly loose). Like wise, couldn't detect obvious damage to what could be seen of the cam lobes. I have had my stethoscope all over the motor, and cannot positively find the origin, though it may be coming from #3, or between #2 & #3.
I have not yet had the head off, or the front cover (would rather not). Is it a cracked piston, damaged valve train, or wasted wrist pin? Something else? How to check? At this point, I am continuing to run the motor on local trips, and it doesn't seem to be getting substantially worse (what's to lose?).