1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 156Get this manual
Install new piston pin lockrings (each side of piston) using Lockring Tool (91-77109A1)Make sure lockrings are properly seated in piston grooves Piston Ring Installation
IMPORTANT: Piston ring side with letter or mark must be facing up
CAUTION
Do not reuse piston pin lockringsUse only new lockrings and make sure they are properly seated in piston groovesPiston Ring
Piston rings are TAPERED top side, and flat (rectangular) on the bottom side (half-keystone rings)
Enlarged View of Piston Ring Grooves
51086Lockring Installation Tool (91-77109A1)Lockring (2)