Inspecting the crankcase halves
- Before proceeding to check the crankcase
halves, thoroughly clean all surfaces and oil ducts.
- On the transmission side crankcase half, take
particular care cleaning the housing and oil ducts
for the following components: the oil pump, the oil
by-pass valve, the main bushings and the cooling
jet on the transmission side (see diagram).
- Take particular care, also, that there are no signs
wear in the oil by-pass valve housing (see Chapter
Lubrication), as this could prevent a good seal in
the piston, which regulates the oil pressure.
N.B.
THE JET IS FED THROUGH THE MAIN BUSHINGS. PROP-
ER OPERATION OF THIS COMPONENT IMPROVES PIS-
TON CROWN COOLING. CLOGGING HAS EFFECTS THAT
ARE DIFFICULT TO DETECT (PISTON TEMPERATURE IN-
CREASE). FAILURE OR LEAKS CAN CAUSE A CONSID-
ERABLE DROP IN THE LUBRICATION PRESSURE FOR
MAIN BUSHINGS AND CONNECTING ROD.
- On the flywheel side crankcase half, take partic-
ular care cleaning the oil ducts for the main bush-
ings, the oil duct for the jet that lubricates the
cylinder head and the oil drainage duct at the fly-
wheel side oil seal.
N.B.
THE HEAD LUBRICATION CHANNEL IS PROVIDED 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 CLOG-
GING IMPAIRS THE HEAD LUBRICATION AND THE TIM-
ING MECHANISMS. A JET FAILURE CAUSES A DE-
CREASE OF THE MAIN BUSHING AND CONNECTING ROD
LUBRICATION PRESSURE.
- Inspect the mating surfaces on the crankcase
halves for scratches or deformation, taking partic-
ular with the surfaces that mate with the cylinder
and the mating surfaces between the crankcase
halves.
- Defects in the crankcase coupling gasket or the
surfaces indicated in the figure can cause a drop
in the oil pressure and affect the lubricating pres-
sure for the main bushings and the connecting rod.
Vespa LX 125 - 150 i.e. Engine
ENG - 133
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