1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 210Get this manual
CYLINDER BLOCKCRANKCASE
Piston Installation
1Assemble connecting rod to piston, secure with piston pin and new piston pin clipIMPORTANT: Reinstall connecting rods in their original positions (top and bottom)Make sure the "Y" mark on the connecting rod is facing up when installed
NOTE: Cylinder bores must be clean before installing pistonsClean with light honing, as necessaryAfter honing, clean cylinder bores with water and detergentAfter cleaning, swab cylinder bores several times with engine oil and clean cloth, then wipe with clean dry cloth110