How do you take a main bearing clearance measurement on a four stroke marine diesel engine?

To measure the main bearing clearance on a four-stroke marine diesel engine, first, ensure the engine is cool and properly secured. Remove the oil pan and main bearing caps, then clean the bearing surfaces. Use a feeler gauge to measure the gap between the crankshaft and the bearing shell; insert the gauge at multiple points around the bearing to account for any uneven wear. Record the measurements to assess if they are within the manufacturer's specified tolerances for proper engine operation.