Derbi Rambla 250, Manual, Page: 130 / 259

DUCE OIL TEMPERATURE. JET CLOGGING IMPAIRS
HEAD LUBRICATION AND THE TIMING MECHANISMS. A
JET FAILURE CAUSES A DROP IN LUBRICATION PRES-
SURE FOR THE MAIN BUSHINGS AND CONNECTING
ROD.
Inspecting the crankshaft plain bearings
- In order to obtain proper bushing lubrication, it is
necessary to have both an outstanding lubricating
pressure (3.2 bar) and a good oil flow rate. There-
fore, the bushings must be correctly positioned 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 influ-
enced by the depth to which the bushings are
driven compared with the crankshaft axial clear-
ance of the limiting surface.
- Measure the bushings diameter at the 3 positions
indicated in the figure.
- Repeat the measurements for the other half of
the bushing. See figure.
Refitting the crankcase halves
Crankcase halves are classified, as are crankshafts, into two categories: Cat. 1 and Cat. 2.
CAUTION
THERE ARE NO STAMPED MARKINGS ON THE ENGINE CRANKCASE HALVES. CRANKSHAFT
CATEGORY MATCHES THE ONE FOR THE ENGINE HALF-SHAFT.
Combine a Cat. 1 shaft with two crankwebs with a Cat. 1 crankcase (or Cat. 2 with Cat. 2).
CAUTION
SHOULD THE CRANKCASE OR CRANKSHAFT BE REPLACED AND BEFORE ORDERING
PARTS, MAKE SURE THE STAMPED MARKING IS CAT. 1 OR CAT. 2 SO THAT YOU RECEIVE
THE SUITABLE MATERIAL FOR A CORRECT COUPLING.
Engine
ENG - 130