Rod bearing failures
Today I found multiple sources for the low end knock. Rod bearing 6 had been spinning for quite a while and wore grooves in the crank and rod.
The rod is definitely unusable. I haven't measured the depth of the crank groove yet but I suspect it's deep enough that the crank is also unusable.
Rod bearing 7 was also spinning but for less time.
The puzzling thing about bearing insert 7 is what happened to the short section that's missing. It wasn't stuck to the journal and I don't think it fell out. Tomorrow I'll check the block thoroughly for it.
Rod bearing 4 had failed but was not spinning.
Rod bearing 8 was also in pretty bad shape.
When I found the excessive clearance for bearings 6 and 7 I became concerned about loss of oil pressure which could affect the camshaft journals and caps. I realized, however, that three rod journals and bearings were in good condition indicating no significant loss of oil pressure. It bugs me that there are no camshaft bearing inserts and if a cap breaks or a bearing surface fails the head is trash. Just because the camshaft spins half as fast as the crankshaft in my opinion does not justify eliminating bearing inserts.
I was going to remove the main bearing caps but my 3/8 inch drive, 6 point 13 mm socket busted in half on the third side bolt. Anyway, I had enough surprises for one day.
Needing a replacement crankshaft and at least one rod has tempted me to purchase a complete stroker rotating assembly if I can find something suitable in my price range. I have lots of research to do and may wait until after I purchase a 2002 or 2003 Explorer to decide how to rebuild the engine.