Sealing Rings - Derbi Rambla 250 Manual

Engine
piston diameter
71.953 ÷ 71.981 mm
Fitting clearance
1st compression ring - standard coupling
0.015 ÷ 0.06 mm
clearance
maximum clearance allowed after use
2nd compression ring - standard coupling
0.015 ÷ 0.06 mm
clearance
maximum clearance allowed after use
oil scraper - standard coupling clearance
÷ 0.06 mm
oil scraper - maximum clearance al-
0.07 mm
lowed after use
Inspecting the cylinder
-Using a bore meter, measure the cylinder inside
diameter at three different points according to the
directions shown in the figure.
- Check that the coupling surface with the head is
not worn or misshapen.
- Pistons and cylinders are classified according to
their diameter. The coupling is carried out in pairs
(M-M, N-N, O-O, P-P).
Characteristic
cylinder: standard diameter
71.990 ÷ 72.018 mm (to 33 mm)
Maximum run-out allowed:
0.05 mm
Inspecting the piston rings

SEALING RINGS

- Alternately insert the 3 sealing rings in the cylin-
der in the area where it keeps its original diameter.
Using the piston, insert the rings perpendicularly
to the cylinder axis.
- 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.
NOTE
BEFORE REPLACING ONLY THE PISTON RINGS, MAKE
SURE THAT COUPLING CLEARANCE BETWEEN THE PIS-
TON RINGS AND ITS GROOVES, AND THAT BETWEEN
ENG - 112
1st compression ring -
0.07 mm
2nd compression ring -
0.07 mm
0.015