1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 189Get this manual
POWERHEAD
5Model 1015 and 1995 and newer Model 9.9: Align hole in center main bearing race with pin of cylinder block
aHolePin (hidden) 6Position alignment boss of upper crankshaft roller bearing into notch in cylinder block7Firmly press retaining ring (bevel faces DOWN) into groove in cylinder block and gently seat crankshaft assembly into position8Gently push seals inward to seat9Check each piston ring for spring tension through transfer and exhaust ports by pressing with screwdriverIf no spring tension exists (ring fails to return to position), it is likely that the piston ring was broken during assembly [replace broken piston rings]Use caution not to burr piston rings while inspecting10Clean crankcase sealing surfaces according to Loctite Master Gasket instructionsApply continuous bead of Loctite sealant along the inside of the mounting bolt holes of crankcase cover