Mercury 40 Service Manual page 227

Valves
1. Clean the carbon deposits from the valve. Discard any cracked, warped, or burned
valves.
2. Measure the valve stem to check for wear. Replace valves if not in specification.
3. Check the valve face for pitting. Valves faces that are pitted must be refaced.
NOTE: Several different types of equipment are available for refacing valves. Follow the
equipment manufacturer's instructions.
IMPORTANT: Do not lap the valves.
4. Check the margin thickness of the valves after the valves have been ground. Any valve
with a margin thickness of less than the specification, should be replaced.
90-828631R3 MARCH 1999
a
Valve Stem Diameter "a"
Intake Valve
Exhaust Valve
45
Margin Thickness "a"
Intake Valve
Exhaust Valve
55810
0.2156 - 0.2161 in.
(5.475 - 5.490 mm)
0.2150 - 0.2156 in.
(5.460 - 5.475 mm)
a
55809
0.020 - 0.035 in.
(0.5 - 0.9 mm)
0.020 - 0.035 in.
(0.5 - 0.9 mm)
CYLINDER HEAD
Page 4A-31