VESPA 633844 IT Service Manual page 19

Vespa GTV 250 i.e.
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 GAUGE, EQUIPPED WITH A SUPPORT, ON
A GROUND PLANE
Name
shimming
shimming
shimming
ENGINE 250 SHIMMING
Measure A
3.70 - 3.60
3.60 - 3.40
3.40 - 3.30
Characteristics
Thickness
0.4 ± 0.05
0.6 ± 0.05
0.8 ± 0.05
CHAR - 13