1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 171Get this manual
POWERHEAD
5Measure cylinder bore diameter (with snap gauge micrometer) at top, middle and bottom of each cylinderCheck for tapered, out-of-round (egg-shaped) and oversize boreIMPORTANT: Ports must be deburred after honing
Crankshaft
1Inspect crankshaft to drive shaft splines for wear2Check crankshaft for straightness [runout 0.076mm (0.003 in]3Inspect crankshaft oil seal surfacesSealing surfaces must not be grooved, pitted or scratchedIf top crankshaft sealing surface is severely worn, replace crankshaftIf bottom crankshaft sealing surface is worn, replace crankshaft coupling seal4Check all crankshaft bearing surfaces for rust, water marks, chatter marks, uneven wear andor overheating (blued)5If necessary, clean up crankshaft bearing surfaces with crocus cloth