Inspecting The Crankcase Halves; Inspecting The Crankshaft Plain Bearings - Gilera GP 800 i.e. Service Station Manual

Engine

Inspecting the crankcase halves

- Before proceeding to check the crankcase halves, thoroughly clean all surfaces and oil ducts.
- Clean the jets and contacts carefully.
N.B.
THE JET IS FED THROUGH THE MAIN BUSHINGS. PROPER OPERATION OF THIS COMPONENT
IMPROVES PISTON CROWN COOLING. CLOGGING HAS EFFECTS THAT ARE DIFFICULT TO
DETECT (PISTON TEMPERATURE INCREASE). FAILURE OR LEAKS CAN CAUSE A CONSID-
ERABLE DROP IN THE LUBRICATION PRESSURE FOR MAIN BUSHINGS AND CONNECTING
ROD .
N.B.
AS ALREADY DESCRIBED IN THE LUBRICATION CHAPTER, IT IS ESPECIALLY IMPORTANT
THAT THE BY-PASS HOUSING SHOWS NO WEAR THAT MAY IMPAIR THE PROPER SEALING
OF THE LUBRICATION PRESSURE ADJUSTMENT PISTON. THE HEAD LUBRICATION CHAN-
NEL IS EQUIPPED WITH A SHUTTER JET; THIS GIVES A "LOW PRESSURE" HEAD LUBRICA-
TION. THIS CHOICE WAS MADE TO REDUCE THE OIL TEMPERATURE IN THE SUMP.
Jet clogging impairs the head lubrication and the timing mechanisms.
A jet failure causes a decrease in the main bearing and connecting rod lubrication pressure.
- Check that the surfaces exhibit no dents or deformations, with special attention to the crankcase
coupling and the crankcase-cylinder surfaces.
- Defects in the crankcase coupling surface gasket can cause a drop in the oil pressure, thus affecting
the lubricating pressure.
- Check the main bearing seats that limit axial clearance in the crankshaft exhibit no wear. For the
dimensional check, refer to the instructions about checking the axial clearance and the dimensions 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.
- The oil feeding channel section is also affected by the bushings driving depth compared with the
crankshaft axial clearance of the limiting surface.
ENG - 76
GP 800 i.e.