1988-1995 Mercury Force 5HP Outboards Service Manual, 90-823263 793, Page 166Get this manual
2 Check flatness of cylinder head Lay cylinder head on piece of plate glassMeasure at different paints between cylinder head and glass with feeler gaugeIf cylinder head is warped 0.012 in(5.0 mm) or less, it should be resurfacedIf warped more than 0.012 in(5.0 mm), replace