BRP Johnson 4HP Service Manual page 89

Valve seat contact width
Measure the valve seat contact width as follows.
1. Remove all carbon from the valve and seat.
2. Coat the valve seat evenly with Prussian Blue (or equiva-
lent).
3. Install the valve into the valve guide.
4. Put the valve lapper on the valve head.
 Valve lapper
5. Rotate the valve while gently tapping the valve contact
area against the seat.
6. Continuously pattern on the valve seating face with Prus-
sian Blue.
7. Measure the valve seat contact width A.
 Vernier calipers
Valve seat contact width A:
Standard: IN 0.8 – 1.0 mm (0.03 – 0.04 in)
EX 1.0 – 1.2 mm (0.04 – 0.05 in)
If measurement exceeds specification, repair valve seat.
NOTE:
For valve seat repair, see "Valve seat servicing" section on
page 6-16.
POWERHEAD
VALVE / VALVE GUIDE
A
6-15