Gilera Nordwest, Workshop Manual

Page: 60 / 136

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 over-
haul 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 gud-
geon pin (with little effort and no lubrication) into the piston and the same gud-
geon 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 re-
spectively the scraper ring is installed with the chamfered side up. (
This ex-
actly 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