1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 148Get this manual
3Push check valve out of carrierIf nylon ball within check valve is stuck or carrier is charred, replace check valve andor carrier as requiredIMPORTANT: SINGLE HOLE side of check valve MUST FACE CRANKCASE
a Crankcase Cover Check Valve Assembly PN 21-42657A1 Valve Restrictor PN 22-814204 Install From Crankshaft Side
Check ValveRestrictor Assembly 7Verify check balls are free to move in check valve case after installationIf check balls are not loose, check valve case was damaged during installation and MUST BE replaced8Reassemble powerhead per appropriate service manual instructions and reinstall on driveshaft housingDESIGN (MODELS WITH CHECK VALVE AND CARRIER)