Piston Clearance; Piston Rings - Yamaha YTZ250S 1986 Service Manual

2.
Using
400-600
grit wet sandpaper, lightly
sand score marks and lacquer deposits
from sides of piston. Sand in crisscross
pattern. Do not sand excessively.
Piston Clearance
1. Measure across the piston skirt diameter
at height "H" as shown .
"H"
Std Piston Skirt Diameter
67.94-68.00 mm (2.675-2.677 in)
H
=
10 mm (0.394 in)
2. Measure cylinder inside diameter
Std Cylinder Inside Diameter
68.00 - 68.02
mm
(2.677 - 2.678
in)
3-15
3. To determine the piston-to-cylinder
clearance, subtract the piston skirt
diameter from the cylinder inside
diameter. Ifthe nominal piston clearance
is not within tolerance, replace the piston
or bore the cylinder as required.
PISTON CLEARANCE
=
Cylinder inside diameter - Piston skirt
deiameter
Exsample:
68.020 mm (2.678 in) - 67.960 mm (2.675 in)
=
0.060 mm (0.002 in)
Std piston clearance
0.060 - 0.065 mm (0.0024 - 0.0026 in)
Piston Rings
1.
Insert ring into cylinder. Push down ap-
proximately 20 mm (0.787 in) using piston
crown to maintain right-angle to bore.
Measure installed end gap. If beyond
tolerance, replace.
Ring end gap installed
0.35-0.50 mm (0.014-0.02 in)