Derbi boulevard 125 4t Workshop Manual page 116

Engine
- Check that there are no signs of wear on the
contact surface with the articulated register termi-
nal.
- If the sealing surface on the valves is wider than
the specified limit, damaged in one or more points
or curved, replace the valve with a new one.
Characteristic
Standard valve length - Inlet:
80.6 mm
Valve standard length: drainage
79.6 mm
- If the checks above give no failures, you can use
the same valves. For best sealing results, it is ad-
visable to grind the valves. Grind the valves gently
with a fine-grained lapping compound. During
grinding, keep the cylinder head in a horizontal
position. This will prevent the lapping compound
residues from penetrating between the valve stem/
guide coupling.
CAUTION
TO AVOID SCORING THE CONTACT SUR-
FACE, DO NOT KEEP ROTATING THE VALVE
WHEN NO LAPPING COMPOUND IS LEFT.
CAREFULLY WASH THE CYLINDER HEAD
AND THE VALVES WITH A SUITABLE PROD-
UCT FOR THE TYPE OF LAPPING COMPOUND
BEING USED.
- Insert the valves into the cylinder head.
- Test the 2 valves alternatively.
- The test is carried out by filling the manifold with
petrol and checking that the head does not ooze
through the valves when these are just pressed
with the fingers.
ENG - 116