Inspecting The Cylinder; Inspecting The Piston Rings - VESPA GTS 250 I.E. Workshop Manual

Vespa GTS 250 I.E.

Inspecting the cylinder

- Using a bore meter, measure the inner cylinder
diameter at three different points according to the
directions shown in the figure.
- Check that the head coupling surface is not worn
or misshapen.
- Pistons and cylinders are classified according to
diameter. The coupling must be made with those
of the same type (M-M, N-N, O-O, P-P).
Characteristic
cylinder: standard diameter
71.990 - 72.018 mm (at 33 mm)
Maximum allowable run-out:
0.05 mm

Inspecting the piston rings

Sealing rings
- Alternately insert the three sealing rings into the
cylinder, in the area where it retains its original di-
ameter. Using the piston, insert the rings perpen-
dicularly to the cylinder axis.
- Measure the opening (see figure) of the sealing
rings using a feeler gauge.
- If any measurements are greater than specified,
replace the piston rings.
N.B.
BEFORE REPLACING ONLY THE PISTON
RINGS, ENSURE THAT THE CLEARANCE BE-
TWEEN THE PISTON RINGS AND THE PISTON
RING GROOVES, AND BETWEEN THE PISTON
AND THE CYLINDER, IS AS SPECIFIED. IN ANY
CASE, NEW PISTON RINGS USED IN COMBI-
NATION WITH A USED CYLINDER MAY HAVE
DIFFERENT BEDDING CONDITIONS THAN
THE STANDARD.
Characteristic
Top piston ring
Standard opening: 0.15 ÷ 0.30 mm
Middle piston ring
Standard opening: 0.20 ÷ 0.40 mm
Engine
ENG - 35