Suzuki DF 25 Service Manual page 146

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 valve.
09916-10911 : Valve lapper
(5) Rotate valve while gently tapping valve contact area against
seat.
(6) Repeat until a continuous pattern in the Prussian blue is
seen.
(7) Measure valve seat contact width A.
09900-20101 : Vernier calipers
Valve seat contact width A
Standard :
IN 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.
NOTE:
For valve seat repair, see "Valve seat servicing" section on page
7-30.
POWER UNIT 7-29