Main Bearing Brass Check - PIAGGIO 500 cc Service Manual

- For the half crankcase flywheel side, pay special
attention to the lubrication ducts to the main bearing
brasses, oil pump compartment and channels, and
by-pass duct situated on the flywheel cover.
N.B.: As already described in Chapter 10-Lubrication, it
is very important that the by-pass housing on the
flywheel cover shows no signs of wear that would
compromise the sealing of the lubrication pressure
adjusting piston. The head lubrication duct is provided
with a choking jet, that provides for a head lubrication of
the "low pressure" type. This is to reduce the oil tem-
perature in the pan.
The jet clogging will prejudice the lubrication to the head
and timing system mechanism.
The jet failure will reduce the lubrication pressure to the
main bearing brasses and connecting rod.
- Check that the surfaces show no signs of dents or
deformation, especially on the cylinder-crankcase
surface and crankcase coupling area.
- A defective gasket and crankcase coupling surface
(see flywheel cover coupling) may cause leaks of the
oil under pressure, thus compromising the lubrication
pressure to the main bearing brasses and connecting
rod.
- Check that the driving shaft end play containment
surfaces show no signs of wear. Check the dimen-
sions according to the procedures described for the
end play check and driving shaft dimensions.

Main bearing brass check

- A good lubrication of the bearing brasses is achieved
with a good lubrication pressure (4 bar) and good oil
flow rate. To this purpose, the bearing brasses must
be positioned correctly to avoid the oil supply ducts
choking.
- The main bearing brasses are obtained with 2 half
bearings, 1 full and 1 with holes and openings for the
lubrication.
- The full half bearing supports the thrusts produced by
the combustion, therefore it is positioned opposite to
the cylinder.
- To avoid the oil supply ducts choking, the coupling
surface of the two half bearings must be perfectly
orthogonal with the cylinder axis, as shown in the
figure.
- The oil supply channels square measure is also
affected by the brass driving depth respect to the
driving shaft end play containment surface.
N.B.: To maintain the brass position on the crankcase,
the driving is forced on cast iron rings that are fitted in
the casting of both half crankcases.
Driving shaft crankcase
05_275
05_276
8 - 13
8