Engine Builders.... Main Bearing Wear? (pics)

[rich81]

Hi guys,

Finished tearing apart an RB25DET bottom end. All the bearings had what looked like particulate wear (dead straight scratch from end to end) like some dirt or somesuch has gotten in between the crank and the bearing.... pretty normal for a 17-year-old engine, right?

But... the centre main bearing had a different wear pattern. I don't know what each side of the bearing is named, so I'm making stuff up here... but the side with the annular groove has dark wear tending toward the centre of the bearing, and the other side has very uneven wear as well.

At this point I'm rebuilding a whole new bottom end from an RB30 block, but since I'm trying to learn more about engine building etc I had to ask... what can cause this type of wear in the bearing? Is it just normal sort of wear to see in a main bearing, or is it caused by bad lubrication, fuel diluted oil, uneven load etc.... dying to know.

I've attached pics, adjusted brightness/contrast so the wear patterns come out easier, and highlighted the bits I'm asking about.

Cheers :-)

[Kinks]

to my untrained eye the first pic looks like a scorch mark (which would be insufficient oil pressure or really old oil). Not sure about the second pic, mainly just bumping the thread so someone weighs in with some more expertise

[Godzilla32]

They look pretty good to me. No deep scratching etc. Its very soft metal so you will always see some wear.