1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 53Get this manual
Starter Cleaning, Inspection and Testing CLEANING AND INSPECTION 1Clean all starter motor parts2Check pinion teeth for chips, cracks or excessive wear3Replace the drive clutch spring andor collar if tension is not adequate or if wear is excessive4Inspect brush holder for damage or for failure to hold brushes against commutator5Replace brushes that are pitted or worn to less than 14 (6.4mm) in length6Inspect the armature conductor (commutator bar junction) for tight connectionA loose connection (excessive heat from prolonged cranking melts solder joints) results in burned commutator bar7Resurface and undercut rough commutator as follows:
11Check the armature for groundSee the following procedure ("Testing")