Mercury Mariner 4, 5, and 6HP 4-Stroke Factory Service Manual, Page 122Get this manual
CYLINDER HEAD
Cylinder Head Resurfacing
1Place 400-600 grit wet sandpaper on flat surface2Resurface the head using figure eight motion until within the specifications
NOTE: Rotate the head several times during the resurfacing procedure to avoid removing to much material from one side
VALVE GUIDE INSPECTION 1Measure the valve guide bore (a)If valve guide wear is out of specification, replace the cylinder head