Gilera 633721 Workshop Manual page 182

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, particularly
with cold oil.
The filter is equipped with an anti-drain back valve and a pressure relief valve; the latter intervenes
when the filtering mass causes a pressure drop above 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 water pump shaft and once at the engine crankcase, to lubricate
the main bearings, the connecting rod head and the piston cooling nozzle, on the transmission-side
bearing.
The main bearing on the transmission side is fitted 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 lubrication.
The camshaft bearings are installed directly on the aluminium of the head; the camshaft axial clearance
is partially compensated by the oil supplied to the smaller diameter bearing.
The camshaft supplies the lubricant to the rocking levers via the holes 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 shut off.
The oil used to lubricate the head returns to the sump via the chain casing channel and therefore it also
provides lubrication for the chain.
A one-way valve and a decantation chamber are used so that gases from the crankcase do not carry
any oil. The one-way valve is a metal reed valve; the decantation chamber has a drainage hole. A failure
in these components implies oil getting into the line supplying air to the engine.
Excessive oil vapours may result in clogged ducts on the throttle body.
In order to signal low oil pressure in the system, a pressure switch is used, located immediately after
the oil filter outlet.
The lubrication circuit does not include the countershaft. The countershaft is lubricated by the oil trans-
ported by the gears 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.
YES - go to 3 NO go to 11
ENG - 182
Nexus 500 euro 3