1988-1992 Mercury Force 5HP Outboards Service Manual, Page 167Get 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
Inspect cylinder block and crankcase for scoring or crackingMeasure cylinder bore with inside micrometer or dial indicator Measure 14 in(6.35 mm) down from topMeasure 14 in(6.35 mm) up from exhaust portMeasure 316 in(4.76 mm) down from intake port