2006 Johnson SD 30 HP 4 Stroke Outboards Service Manual, PN 5006592, Page 146Get this manual
POWERHEAD CYLINDER HEAD The service limit for valve head radial runout is 0.003 in(0.08 mm)If the measurement exceeds this specification, replace the valve Measure the valve seat contact width as follows: Remove all carbon deposits from the valve and the valve seat Coat the valve seat evenly with Prussian blue (or equivalent) Install the valve into the valve guide Place valve lapper on the valve Rotate the valve while gently tapping the valve contact area against the seatRepeat until continuous pattern in the Prussian Blue is seen