Gilera 633721 Workshop Manual page 150

Engine
- If the checks above give no failures, you can use
the same valves. To obtain better sealing perform-
ance, grind the valve seats. Grind the valves gently
with a fine-grained lapping compound. During the
grinding, keep the cylinder head with the valve ax-
es in a horizontal position. This will prevent the
lapping compound residues from penetrating be-
tween the valve stem and the guide (see figure).
CAUTION
TO AVOID SCORING THE FAYING SURFACE, DO NOT KEEP ROTATING THE VALVE WHEN NO
LAPPING COMPOUND IS LEFT. CAREFULLY WASH THE CYLINDER HEAD AND THE VALVES
WITH A SUITABLE PRODUCT FOR THE TYPE OF LAPPING COMPOUND BEING USED.
CAUTION
DO NOT REVERSE THE FITTING POSITIONS OF THE VALVES (RIGHT - LEFT).
Inspecting the springs and half-cones
- Check that the upper spring caps and the cotter
halves show no signs of abnormal wear.
- Measure the unloaded spring length.
Characteristic
Standard length:
44.4 mm
Admissible limit after use:
42.4 mm
ENG - 150
Nexus 500 euro 3