PIAGGIO B 250 - Page 147

Diameter of the wrist pin seat on the piston:
Standard clearance
0.001 ÷ 0.010 mm
piston diameter
71.953 - 71.981 mm
Fitting clearance
Top piston ring - standard coupling clearance
0.015 - 0.06 mm Top piston ring - maximum clear-
ance allowed after use 0.07 mm Middle piston
ring - standard coupling clearance 0.015 - 0.06 mm
Middle piston ring - maximum clearance al-
lowed after use 0.07 mm oil scraper ring - stand-
ard coupling clearance 0.015 - 0.06 mm oil scraper
ring - maximum clearance allowed after use
0.07 mm
Inspecting the cylinder
Version 250
- Using a bore gauge, measure the internal diam-
eter of the cylinder following the directions given in
the figure and at three different heights.
- Check that the plane of coupling with the head
does not show wear or deformations.
- The pistons and cylinders are classified with cat-
egories depending on the diameters. The coupling
is carried out matched (A-A, B-B, C-C, D-D).
Characteristic
cylinder: standard diameter
71.990 - 72.018 mm (at 33 mm)
Maximum allowable run-out:
0.05 mm
Version 125
B 125-250 Engine
ENG - 147