1996-2005 Suzuki DF40, DF50 Four Stroke Outboard Service Manual, Page 176Get this manual
6-33 POWER UNIT 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 (or equivalent) (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) Continuously pattern on valve seating face with Prussian blue(7) Measure valve seat contact width A09900-20101Vernier calipers Valve seat contact width StandardIN 1.80 2.20 mm (0.071 0.087 in EX 1.65 2.05 mm (0.065 0.081 in If measurement exceeds specification, repair valve seat