Gilera 633721, Workshop Manual

Page: 173 / 407

Inspecting the crankcase halves
- Before proceeding to check the crankcase
halves, thoroughly clean all surfaces and oil ducts.
- For the transmission-side half-crankcase, special
attention should be given to the bushings, to the
cooling jet on the transmission side (see figure)
and to the lubrication duct.
N.B.
THE JET IS FED THROUGH THE MAIN BUSHINGS. PROP-
ER OPERATION OF THIS COMPONENT IMPROVES THE
PISTON TOP COOLING. CLOGGING HAS EFFECTS THAT
ARE DIFFICULT TO DETECT (PISTON TEMPERATURE IN-
CREASE). FAILURE OR LEAK CAN CONSIDERABLY DE-
CREASE THE MAIN BUSHING AND CONNECTING ROD
LUBRICATION PRESSURE.
- For the flywheel side half-crankcase, special at-
tention should be given to the lubrication channels
for the main bearings and to the compartment and
the channels for the oil pump, as well as to the duct
for the by-pass located on the flywheel cover.
N.B.
AS ALREADY DESCRIBED IN THE "LUBRICATION" CHAP-
TER, IT IS ESPECIALLY IMPORTANT THAT THE BY-PASS
HOUSING ON THE FLYWHEEL COVER IS FREE FROM
WEAR THAT MAY IMPAIR THE PROPER SEALING OF THE
LUBRICATION PRESSURE ADJUSTMENT PISTON. THE
HEAD LUBRICATION CHANNEL IS EQUIPPED WITH A
SHUTTER JET; THIS GIVES A "LOW PRESSURE" HEAD
LUBRICATION. THIS CHOICE WAS MADE TO REDUCE
THE OIL TEMPERATURE IN THE SUMP.
The jet clogging impairs the head lubrication and the timing mechanisms.
A jet failure causes a decrease in the main bearing and connecting rod lubrication pressure.
- Check that the surfaces exhibit no dents or deformations, with special attention to the crankcase
coupling and the crankcase-cylinder surfaces.
- Any defects in the crankcase gasket or matching surfaces (see Flywheel cover coupling) can cause
pressurised oil leaks, thereby affecting the connecting rod and main bearing lubrication pressure.
- Check the main bearing seats that limit axial clearance in the crankshaft show no signs of wear. For
the dimensional check, refer to the instructions about checking the axial clearance and the dimensions
on the crankshaft
Nexus 500 euro 3
Engine
ENG - 173