We recently got a garden-variety 83 320i/a M10 and are in midst of renewal. 200k plus miles with benign neglect it seems. Before teardown engine ran strong and no blue smoke, etc., beyond little-bit at start-up after sitting.

Last night we pulled oil pan and pic's of #4 show what appears to be either rust or sludge build-up on lower bore walls. Cross-hatching looks decent and didn't see any real vertical scratches. Lot of sludge build-up though no bits or chunky stuff in pan. (Oil Pump Chain seems pretty loose, but not sure how tight its supposed to be.)

Realize it could be many different things but would really appreciate any insights. As engine is open, is full rebuild advisable in any event? Thanks!

#4.jpg #4 Cyl.jpg IMG_5456.jpg IMG_5450.jpg IMG_5463.jpg