VESPA 946 E4 EMEA 2021 Manual page 179

Vespa 946 E4-E5 EMEA-USA-ASIA (2021-)
Inspecting the crankshaft alignment
N.B.
TO MEASURE WEAR LIMITS AND COUPLING CLEARANCES, SEE THE SPECIFICATIONS CHAP-
TER.
See also
Crankcase - crankshaft - connecting rod
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 when handling the oil pump compartment
and the oil ducts, the by-pass duct, the main bushings and the cooling jet on the transmission side.
- 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.
- On the flywheel side crankcase half, take particular care cleaning the oil ducts for the main bushings,
the oil duct for the jet that lubricates the cylinder head and the oil drainage duct at the flywheel side oil
seal.
- Inspect the coupling surfaces on the crankcase halves for scratches or deformation, taking particular
care with the cylinder/crankcase surfaces and the crankcase halves surfaces.
- Defects in the crankcase coupling gasket between the crankcase halves or the mating surfaces shown
in the diagram, could cause a drop in the oil pressure lubricating the main bushings and connecting
rod.
- Check the main bearing seats that limit axial clearance in the crankshaft show no signs of wear. The
dimension between these seats is measured by way of the procedure described previously for meas-
uring the crankshaft axial clearance and dimensions.
N.B.
THE JET IS FED THROUGH THE MAIN BUSHINGS. PROPER OPERATION OF THIS COMPONENT
IMPROVES PISTON CROWN COOLING. CLOGGING HAS EFFECTS THAT ARE DIFFICULT TO
DETECT (PISTON TEMPERATURE INCREASE). FAILURE OR LEAKS CAN CAUSE A CONSID-
ERABLE DROP IN THE LUBRICATION PRESSURE FOR MAIN BUSHINGS AND CONNECTING
ROD.
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 TEMPER-
ATURE IN THE SUMP. THE JET CLOGGING IMPAIRS THE HEAD LUBRICATION AND THE TIMING
MECHANISMS. A JET FAILURE CAUSES A DECREASE OF THE MAIN BUSHING AND CON-
NECTING ROD LUBRICATION PRESSURE.
Engine
ENG - 179