Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 113Get this manual
CYLINDER HEAD
Cylinder Head Resurfacing
1Place 400-600 grit wet sandpaper on flat surface2Res urface the head using figure eight motion until within the specificationsNOTE: 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