Main bearing question!!!!

[20fan20]

We pulled our engine apart and all the main bearing looked good except for the 3rd main back it looked to have some excessive wear.... what could be my problem?

[dereksehi]

Check to see if that housing bore is tighter than the rest causing that bearing to have less clearance or your crankshaft could be bent as the center main will have the worst runout.

[Brian Gray]

most likely that bore was tighter than the rest. look at all the bearing halve part numbers first take notes . then measure your bores installed at torque. now measure the mains on the crank.

I see this a lot
if you notice that there are main bearing halves with an "x" mixed in the batch these are + clearance bearings. the ones in the main caps should all match and the add ons should only be mixed in the oil feed side. I some times get engines in that have the clearance halves in the main cap this causes more load to be placed on the less clearance halves witch in turn equals higher wear and a more likely chance of main bearing failure.