Derbi boulevard 125 4t Workshop Manual page 138

Engine
Removing the oil sump
- Remove the oil filler plug, the transmission cover,
the complete drive pulley assembly with belt and
the sprocket wheel, as described in the Transmis-
sion chapter.
- Drain the oil from the sump as described above.
- Remove the 7 screws indicated in the figure and
the 2 rear brake transmission fixing brackets.
- Remove the spring, the by-pass piston and the
gasket shown in the second image.
Inspecting the by-pass valve
- Check the unloaded spring length.
- Check that the small piston is not scored.
- Ensure that it slides freely on the crankcase and
that it guarantees a good seal.
- If not, eliminate any impurities or replace defec-
tive parts.
Characteristic
By-pass check up: Standard length
54.2 mm
ENG - 138