Suzuki DF25/DF30 Four Stroke Service Manual, Page 146Get this manual
POWER UNIT 7-29 Valve seat contact width Measure valve seat contact width as follows: (1) Remove all carbon from valve and seat(2) Coat valve seat evenly with Prussian blue (orequivalent) (3) Install valve into valve guide(4) Put valve lapper on valve09916-10911Valve lapper (5) Rotate valve while gently tapping valve contact area against seat(6) Repeat until continuous pattern in the Prussian blue is seen(7) Measure valve seat contact width A09900-20101Vernier calipers Valve seat contact width StandardIN 1.3 1.5 mm (0.05 0.06 in EX 1.3 1.5 mm (0.05 0.06 in If measurement exceeds specification, repair valve seat