2006 Johnson SD 30 HP 4 Stroke Outboards Service Manual, PN 5006592, Page 153Get this manual
POWERHEAD PISTON, CYLINDER, AND CRANKSHAFT
WARNING
Inspection and Servicing
Cylinder
Use straightedge and thickness gauge to measure the cylinder distortion on the gasket surface at six (6) locations as shownThe service limit for distortion is 0.0012 in(0.03 mm)If any measurement exceeds this specification, resurface or replace the cylinderThe cylinder can be resurfaced using surface plate and #400 grit wet sandpaperMove the cylinder in figure eight pattern when sanding