APRILIA SCARABEO 500 - 2008, Service Station Manual

Page: 176 / 324

- Pistons and cylinders are classified according to their diameter. This coupling is carried out in pairs
(A-A, B-B, C-C, D-D).
NOTE
TO MEASURE THE CYLINDER AND THE CYLINDER-PISTON COUPLING CLEARANCE REFER
TO THE «SPECIFICATIONS» SECTION.
Inspecting the piston rings
- Alternately fit the 3 sealing rings in the cylinder in
the area where it keeps its original diameter. Using
the piston, fit the rings perpendicularly to the cyl-
inder axis.
- Check that each single sealing ring adheres uni-
formly to the cylinder liner. Otherwise, it means
there is abnormal wear on the ring. Replace it if
this occurs.
- Measure the opening of the sealing rings using a
thickness gauge (see picture).
- Replace the piston rings if values higher than
those prescribed are measured.
Check the size of the sealing ring opening:
Compression ring: 0.15 ÷ 0.35 mm. Max. value: 0.5 mm
Oil scraper ring: 0.25 ÷ 0.50 mm. Max. value: 0.65 mm
Oil scraper ring: 0.25 ÷ 0.50 mm. Max. value: 0.65 mm
Rings/slots coupling clearances:
Carefully clean the sealing ring housings.
Check coupling clearances by placing a thickness
gauge between the ring and the slot as shown in
the figure.
Top ring: Standard coupling clearance:
0.01÷0.06 mm
Maximum clearances allowed after use: 0.10
mm
Middle ring: Standard coupling clearance:
0.02÷0.07 mm
Maximum clearances allowed after use: 0.10
mm
Oil scraper ring: Standard coupling clear-
ance: 0.01÷0.06 mm
Engine
SCARABEO 500
ENG - 176