1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 220Get this manual
CYLINDER BLOCKCRANKCASE
2Install powerhead gasket and dowel pins
NOTE: Do not re-use powerhead gaskets (2)3Place powerhead onto drive shaft housing secure powerhead with boltsTorque powerhead bolts in sequence
NOTE: Powerhead bolts should be clean and dry prior to installation4Install dipstick5