2006 SD Johnson 4 Stroke 9.9-15HP Outboards Service Repair Manual P/N 5006590, Page 148Get this manual
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POWERHEAD CYLINDER ASSEMBL Measue
valve seat contact widthService limit: 0.035 to 0.043 in (0.9 to 1.1 If measurement exceeds service limit, repair valve seatRefer to Valve Seat Servicing