1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 169Get this manual
POWERHEAD
Powerhead Cleaning and Inspection
Cylinder Block and Crankcase Cover
IMPORTANT: Crankcase cover and cylinder block are matched, line-bored assembly and must be replaced as set1Thoroughly clean cylinder block and crankcase coverVerify that all sealant and old gaskets are removed from mating surfacesRemove all carbon deposits from exhaust ports, decompression ports and cylinder dome2Inspect cylinder block and crankcase cover for cracks or fractures3Check gasket surfaces for nicks, deep grooves, cracks and distortion4Inspect all water and fuel passages in cylinder block and crankcase cover for obstructions5Verify that all fittings and plugs are tight
aDecompression ports