VESPA GTS Super 300 ie 2008, Service Station Manual

Page: 166 / 317

- Inspect the coupling surfaces on the crankcase
halves for scratches or deformation, taking partic-
ular care with the cylinder/crankcase surfaces and
the crankcase halves surfaces.
- Defects in the crankcase coupling gasket be-
tween 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
measuring the crankshaft axial clearance and di-
mensions.
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.
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.
Inspecting the crankshaft plain bearings
- To obtain a good bushing lubrication it is necessary to have both an optimal lubricating pressure and
a good oil flow rate; the bushings must be correctly positioned so as not to obstruct the oil supply
channels.
- The main bushings are comprised of two half-bearings, one with holes and channels for lubrication
whereas the other is solid.
Characteristic
Lubrication pressure
3.5 to 4 bar
Engine
Vespa GTS Super 300 ie (2008)
ENG - 166