1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 160Get this manual
CYLINDER HEAD
NOTE: When loosening lock nuts, hold the adjusting screw with screw driver to prevent it from moving
3Perform the following adjustment steps: Turn the driven gear and align the "1 ormark on the driven gear with the "" mark on the cylinder blockAdjust the intake and exhaust valve clearance for cylinder #1Turn the driven gear 180 (crank shaft 360) and align the "2 ormark on the driven gear with the "" on the cylinder blockAdjust the intake and exhaust valve clearance for cylinder #2