1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 281Get this manual
NON BIGFOOT GEAR HOUSING
Impeller and Pump Cover Installation
1Install lower neoprene washer2Install drive keyUse 2-4-C wTeflon to hold key to drive shaftIMPORTANT: It is recommended that the impeller be replaced regardless of appearanceIf impeller must be reused, it must be installed in the direction of original rotationInstalling impeller with vanes reversed from their previous "set" will result in vane breakage shortly after unit is returned to service3Install new impeller and align with drive key4Install upper neoprene washer5Lubricate I.Dof water pump cover with 2-4-C wTeflon6Install cover on drive shaft and while pushing down on cover, rotate drive shaft CLOCKWISE and install cover over impeller