2006 Johnson SD 30 HP 4 Stroke Outboards Service Manual, PN 5006592, Page 140Get this manual
POWERHEAD CYLINDER HEAD
Inspection and Servicing
Cylinder Head
Remove all carbon deposits from the combustion chambersDO NOT use any sharp edged tool to scrape off carbonBe careful not to scuff or nick the metal surfaces
The cylinder head can be resurfaced using surface plate and #400 grit wet sandpaperMove the cylinder head in figure eight pattern when sanding
Check for cracks in the intake and exhaust ports, the valve seats, the combustion chambers, and the surface of the cylinder headExhaust valve seat Intake valve seat