1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 206Get this manual
CYLINDER BLOCKCRANKCASE
8Remove the bolts and crankcase9Measure the compressed plastigauge to check the main bearing clearanceReplace bearings if clearance is not within specification57577
a-Compressed Plastigauge SELECTING NEW MAIN BEARINGS 1Locate the main bearing code letters on the crankcasea-Main Bearing Code Letters b-Bearing Color 2Refer to the following reference chart to select the correct main bearings3Use the color coded main bearings that match the main bearing code letterCRANKCASE AND BEARING INDICATION MARKS Main Bearing Code Letter Main Bearing Color Code Blue Black Brown