VESPA GTV 250 i.e. 2008 Service Station Manual page 20

Technical Data
Measurement "A" to be taken is a value of piston re-entry, it indicates by how much the plane formed
by the piston crown falls below the plane formed by the top of the cylinder. The further the piston falls
inside the cylinder, the less the base gasket to be applied (to recover the compression ratio) and vice
versa.
N.B.
MEASUREMENT "A" MUST BE TAKEN WITHOUT ANY GASKET FITTED BETWEEN THE CRANK-
CASE AND CYLINDER AND AFTER RESETTING THE DIAL GAUGE, EQUIPPED WITH A SUP-
PORT, ON A GROUND PLANE
Name
shimming
shimming
shimming
DT - 20
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