VESPA GTV 250 i.e. 2008 Service Station Manual page 126

Engine
THE TOP OF THE CYLINDER. THE FURTHER THE PISTON FALLS INSIDE THE CYLINDER, THE
LESS THE BASE GASKET IS TO BE APPLIED (TO RECOVER THE COMPRESSION RATIO) AND
VICE VERSA.
Name
shimming
shimming
shimming
Refitting the piston rings
Fitting the sealing rings
- Place the oil scraper spring on the piston.
- Refit the oil scraper ring with the join of spring
ends on the opposite side from the ring gap and
the word 'TOP' towards the piston crown. The
chamfered side of the oil scraper ring should al-
ways be facing the piston crown.
- Fit the middle piston ring with the identification
letter facing the piston crown. In any case, the step
must be facing opposite the piston crown.
- Fit the top piston ring with the word 'TOP' or the
reference mark facing the crown of the piston.
- Offset the piston ring gaps on the three rings by
120° to each other as shown in the figure.
- Lubricate the components with engine oil.
- The top piston ring on the 250 engine has an L
cross section.
N.B.
THE TWO PISTON RINGS ARE MADE WITH A TAPERED
CYLINDRICAL CONTACT CROSS-SECTION. THIS IS TO
ACHIEVE A BETTER BEDDING.
ENG - 126
ENGINE 250 SHIMMING
Measure A
3.70 - 3.60
3.60 - 3.40
3.40 - 3.30
Vespa GTV 250 i.e.
Thickness
0.4 ± 0.05
0.6 ± 0.05
0.8 ± 0.05