PIAGGIO 633929(IT), Service Station Manual, Page: 148 / 314

ERABLY DECREASE THE MAIN BUSHING
AND CONNECTING ROD LUBRICATION PRES-
SURE.
N.B.
THE HEAD LUBRICATION CHANNEL IS PRO-
VIDED 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 LUBRICA-
TION AND THE TIMING MECHANISMS. A JET
FAILURE CAUSES A DECREASE OF THE MAIN
BUSHING AND CONNECTING ROD LUBRICA-
TION PRESSURE.
Inspecting the crankshaft plain bearings
- T
o obtain a good bushing lubrication it is necessary
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 chan-
nels, the matching surface of the two half-bearings
must be perfectly perpendicular to the cylinder ax-
is, 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.
- Check the inside diameter of the main bushings
in the three directions indicated in the diagram.
- Repeat the measurements for the other bushing
half. see diagram.
- There are three crankcase versions: with RED
main bushings, with BLUE main bushings and with
YELLOW main bushings.
Engine
MP3 125
ENG - 54