Gilera SATURNO BIALBERO 350 Workshop Manual page 60

CYLINDER - PISTON 8 - 2
Piston rings
The rings are removed only when necessary.
These components are very fragile and must be removed and installed
very carefully.
To check for ring wear, take each ring and place it "squarely" inside the
lower part of the cylinder. Measure the end gap with a feeler gauge
(fig. 9).
Max. gap = 0.8 mm (350cc) 1 mm (500cc)
Make sure the rings have play (but not excessive) in their grooves (see
overhaul table on page 1 - 5 (PISTON/CYLINDER MATCHING CHART)
Gudgeon pin
Make sure the gudgeon pin doesn't have an excessive radial clearance,
both around the connecting rod and piston.
Max. clearance piston / gudgeon pin = 0.06 mm
Max. clearance small end / gudgeon pin = 0.08 mm
For the most part, a satisfactory check can be carried out by sliding the
gudgeon pin (with little effort and no lubrication) into the piston and the
same gudgeon pin must not slide out by its own weight.
The water pump cannot be overhauled; if found damaged or worn, it
must be replaced as a unit.
Check that the thermostat isn't damaged or scaled.
Verify that it starts to open at 75°C and that it is fully opened at 85°C.
Check condition of the thermostat's O-ring.
REASSEMBLY
Assemble in reverse order of disassembly. Pay close attention to the
following points:
Piston rings are installed in a specific order and direction. The first two
rings are marked with the letters "TOP 2" and "TOP" for the first and
second ring respectively the scraper ring is installed with the chamfered
side up. (This exactly how it appears in the official manual, however the
consensus of opinion is that it should read "TOP and TOP 2").
The piston must be installed in one direction only; the 350cc engine has
arrow marked on top of piston; for the 500cc engine, mark piston before
removal.
Always use new gaskets, O-rings and gudgeon pin lockrings.
Thoroughly oil the cylinder wall before fitting the piston; piston rings end
gap must be spaced throughout the circumference of the piston.
Do not forget the rubber O-ring that is placed around the oil feed line at
the base of the cylinder.
The cylinder is mounted to the base with two bushing guides around the
two studs.
The starter motor's idler gear bolt is mounted with the milled part facing
up (fig. 11).
8 - 2,3