Inspecting The Crankshaft Plain Bearings - PIAGGIO MP3 400 i.e. Service Manual

MP3 400 i.e.
- For the flywheel side half-crankcase, special at-
tention should be given to the lubrication channels
for the main bearings and to the compartment and
the channels for the oil pump, as well as to the duct
for the by-pass located on the flywheel cover.
N.B.
AS ALREADY DESCRIBED IN THE "LUBRICA-
TION" CHAPTER, IT IS ESPECIALLY IMPOR-
TANT THAT THE BY-PASS HOUSING ON THE
FLYWHEEL COVER IS FREE FROM WEAR
THAT MAY IMPAIR THE PROPER SEALING OF
THE LUBRICATION PRESSURE ADJUSTMENT
PISTON. THE HEAD LUBRICATION CHANNEL
IS PROVIDED WITH A SHUTTER JET; THIS
GIVES A "LOW PRESSURE" HEAD LUBRICA-
TION. THIS CHOICE WAS MADE TO REDUCE
THE OIL TEMPERATURE IN THE SUMP.
The jet clogging impairs the head lubrication and the timing mechanisms.
A jet failure causes a decrease of the main bearing and connecting rod lubrication pressure.
- Check that the surfaces are free from dents or deformations, with special attention to the crankcase
coupling and the crankcase-cylinder surfaces.
- Any defects in the crankcase gasket or matching surfaces (see Flywheel cover coupling) can cause
pressurised oil leaks, thereby affecting the connecting rod and main bearing lubrication pressure.
- Check the main bearing seats that limit axial clearance in the crankshaft show no signs of wear. For
the dimensional check, refer to the instructions relating to the axial clearance and dimensions check on
the crankshaft

Inspecting the crankshaft plain bearings

- To obtain a good bushing lubrication it is neces-
sary to have both an optimal lubricating pressure
(4 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.
Engine
ENG - 87