PIAGGIO Beverly Tourer 250 i.e. Service Station Manual page 145

Beverly Tourer 250 i.e.
- 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 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.
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 neces-
sary to have both an optimal lubricating pressure
(3.2 bar) 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 lubrica-
tion whereas the other is solid.
- The solid half-bearing is intended to stand the thrusts caused by combustion, and for this reason it is
arranged opposite the cylinder.
- To prevent obstructions in the oil feeding channels, the matching surface of the two half-bearings must
be perfectly perpendicular to the cylinder axis, as shown in the figure.
- The oil feeding channel section is also affected by the bushings driving depth compared with the
crankshaft axial clearance of the limiting surface.
N.B.
TO KEEP THE BUSHINGS ON THE CRANKCASE IN SUCH POSITION, DRIVING IS FORCED ON
CAST-IRON RINGS INSERTED IN THE CASTING OF BOTH CRANKCASE HALVES.
N.B.
TO MEASURE WEAR LIMITS AND COUPLING CLEARANCES, SEE THE SPECIFICATIONS CHAP-
TER.
See also
Engine
ENG - 145