Diagnosis Guide - Gilera Nexus 500 Workshop Manual

Engine
The pump is controlled by means of a piston by-pass calibrated to 4 bar. This is located before the
cartridge filter and both are installed on the flywheel cover, so that the seal of the filter is subject to the
pressure of the circuit.
The by-pass located before the cartridge filter improves the operating conditions for the filter proper,
particularly with cold oil.
The filter is equipped with an anti-cavitation valve and a pressure relief valve; the latter intervenes when
the filtering element causes a pressure drop exceeding 1± 0.2 bar.
These conditions naturally occur only with cold oil and at high engine revs or if the filter is clogged.
The filtered oil is used to lubricate the shaft of the water pump and once at the engine crankcase, to
lubricate the crankcase bearings, the connecting rod head and the piston cooling nozzle located on the
bearings on the transmission side.
The crankcase bearing on the transmission side is provided with an oil seal and the respective drain
line.
The supply line for the timing system comes from the flywheel-side bearing; the supply to the head is
controlled by the respective spray jets in the engine crankcase.
The components of the timing system function with low-pressure oil.
The camshaft bearings are marked directly on the aluminium of the head; the axial clearance of the
camshaft is partly compensated by the oil supplied to the small end bearings.
The camshaft supplies the lubricant to the rocking levers via the bores provided; these are installed in
a position to ensure that the lubrication is maintained even after the scooter has stopped. This is ach-
ieved when the camshaft reaches its most usual and likely position when the engine is switched off.
The oil used to lubricate the head returns to the sump via the ducts in the chain casing and hence also
provides lubrication for the chain.
In order to avoid the gas collecting in the bottom of the tank carrying oil out of the housing, a non-return
valve and a decantation chamber are used. The one-way valve is of metal sheet design; the decantation
chamber is provided with a drainage bore. If they fail oil can get into the pipe supplying air to the engine.
Excessive oil vapours may result in a blockage in the ducts of the throttle body.
In order to signal low oil pressure in the circuit, a pressure switch is used, located immediately after the
oil filter outlet.
The lubrication circuit does not include the countershaft; its lubrication comes from the oil transported
by the gearing or by the centrifugal effect of the crankshaft.
The same applies to the piston or the pin, but in this case the cooling nozzle is particularly important.

Diagnosis guide

1 - Minimum oil pressure warning light on with hot engine.
AHEAD - go to 2
2 - Remove the minimum pressure switch electric connector.
Check that the warning light turns off.
ENG - 102
Nexus 500