Son bought an 88 Isuzu I-Mark (1.5l, non-turbo, carbureted). Prev. owner provided lots of repair bills. Her son had taken the engine out by not monitoring oil level, even with a known rear seal leak. Given the age of the car, they got a replacement engine from an auto wrecker. Rear seal leaked on that, as well, so they had that replaced.
Motor is clean; didn't make any noise during a warm look-over, or during the test drive the next day. But since then, it has developed a real knock. From above, it doesn't even sound like its definitively engine knock, but we had it on the hoist at my father-in-law's, and from underneath, it sounds like the world is ending....
Engine has to warm up to get noisy. Knock is quite quiet at idle, but gets worse with RPM. Seems to be worse at steady load (as opposed to higher load from acceleration, or no-load when coasting down). Had the pan off; rod bearings have a little scoring (187 000 km engine), but NO visible color change or such to indicate wear. (sorry, didn't have Plastigauge that day to check) Mechanic's stethoscope run around on the engine doesn't point me to anything. Noise seems to be worse from outside. Doesn't seem to be timing belt slap, or anything like that. Engine does not appear to have a harmonic balancer, either.
The only thing I can think of is possibly a wrist pin. Anybody have any other thoughts?
Thanks in advance. DanR