APRILIA SCARABEO 500 - 2008, Service Station Manual

Page: 208 / 324

Inspecting the crankshaft plain bearings
- In order to obtain proper bushing lubrication,
make sure there are both an outstanding lubrica-
tion pressure (4.5 bar) and a good oil flow rate. To
that end, the bushings must be correctly posi-
tioned so as not to obstruct the oil supply channels.
- The main bushings are comprised of 2 half-bear-
ings, one with holes and channels for lubrication
while the other is solid.
- The solid half-bearing is intended to stand the thrusts caused by combustion, and for this reason, it is
arranged opposed to the cylinder.
- So as not to obstruct the oil supply channels, the coupling surface of the two half-bearings must be
perpendicular to the cylinder axis as shown in the figure.
- The oil supplying channel section is also influenced by the depth to which the bushings are driven
compared with the crankshaft axial clearance of the limiting surface.
NOTE
TO KEEP THIS POSITION OF THE BUSHINGS ON THE CRANKCASE, FITTING IS FORCED ON
CAST IRON RINGS INSERTED IN THE CASTING OF CRANKCASE HALVES.
- Measure the bushings diameter at the 3 positions
indicated in the figure.
- Repeat the measurements for the other half of
the bushing. See figure.
NOTE
DO NOT TAKE THE MEASUREMENT ON BOTH
HALF-SHELLS COUPLING SURFACE SINCE
THE ENDS ARE RELIEVED TO ALLOW BEND-
ING DURING THE DRIVING OPERATION.
Before fitting, check that the clearance between the engine crankcase bushing and the crankshaft is
within the predetermined limits.
Characteristic
Crankshaft-bushing maximum clearance allowed:
0.08 mm
- The standard bushing diameter after driving varies according to a coupling selection.
- The crankcase bushing seats are classified into 3 categories while the crankshaft ones, into 2 cate-
gories.
- The main bushings are subdivided into 4 categories according to thickness (see table).
Engine
SCARABEO 500
ENG - 208