So I'm just finishing up putting new bearings into the bottom end of my 1989 Chevy K2500 with the factory TBI 350. I was wondering if I needed to do a break in period for the main and rod bearings. The original crank spec'ed out with in limits on the micrometer, dial indicator, and plastigage so I did not replace or machine it. I did not pull the heads, rods, pistons, or anything on the top side for that matter. The origin of my question comes from something I believe to have remembered in diesel tech college about the reason for a break in period is for allowing the junk from seating the new piston rings to drain out with the oil. Given I didn't touch the pistons or cylinders, would I be correct to assume I do not need to run a break in period?

 

Run it. Personally though, I would do an early oil change for good measure. Around 500 miles, ensure things look normal and then never look back.