Mercury Force 9.9, 15HP Outboards Service Manual, Page 132Get this manual
7Check crankshaft for damage Inspect threads on end of crankshaftInspect keyway and tapered ends for scoring or wearCheck upper main bearing for restricted movement, cracksand wear NOTE: Replace bearing if worn or damagedIt would be advisable to have an automotive machine shop remove and replace the upper bearingInspect lower crankshaft seal and bearing Replace if damaged or worn