4-15
CYLINDER HEAD, CYLINDER AND PISTON
CHECKING THE PISTON
1. Eliminate:
• Carbon deposits
From the piston crown "a" and
ring groove "b".
2. Inspect:
• Piston wall
Score marks
→
Repair or replace.
3. Measure:
• Piston skirt diameter
Use micrometer "1".
Measure the specific distance "a"
from the bottom edge.
Out of specification
→
Replace.
CHECKING THE PISTON PIN AND
SMALL END BEARING
1. Inspect:
• Piston pin
• Small end bearing
Signs of heat discoloration
→
Re-
place.
2. Measure:
• Piston pin outside diameter
Use micrometer "1".
Out of limit
→
Replace.
3. Check:
• Free play (when the piston pin "1"
is in place in the piston "2")
There should be no noticeable for
the play.
Free play exists
→
Replace piston
pin and/or piston.
4. Install:
• Small end bearing
• Piston pin
Into the small end of connecting
rod.
5. Check:
• Free play
There should be no noticeable
free play.
Free play exists
→
Inspect the
connecting rod for wear/Replace
the pin and/or connecting rod as
required.
CHECKING THE PISTON RING
1. Install:
• Piston ring
Into the cylinder.
Push the ring with the piston
crown.
2. Measure:
• End gap
Use a thickness gauge "1".
Out of limit
→
Replace.
3. Measure:
• Side clearance
Use a thickness gauge "1".
Out of limit
→
Replace piston and/
or ring.
Check at several points.
Standard
Wear limit
Cylin-
der bore
"C"
54.000–
54.014 mm
(2.1260–
2.1265 in)
54.1 mm
(2.130 in)
Taper
"T"
—
0.05 mm
(0.0020 in)
"C" = Maximum Aa–Cb
"T" = (Maximum Aa, or Ab) - (Max-
imum Ba, or Bb)
Distance
"a"
Piston dia.
17.5 mm
(0.69 in)
53.957–53.972
mm (2.1243–
2.1249 in)
Piston pin outside diam-
eter:
Standard
<Limit>
14.995–15.000
mm (0.5904–
0.5906 in)
14.975 mm
(0.5896 in)
Ring end gap (installed):
Standard
<Limit>
0.5–0.7 mm
(0.020–0.028 in)
1.2 mm (0.047
in)
Side clearance:
Standard
<Limit>
0.035–0.070
mm (0.0014–
0.0028 in)
0.1 mm (0.004
in)
Summary of Contents for YZ125X1
Page 2: ...1C3 9 33_cover 07 6 14 9 59 AM Page 2...
Page 3: ...YZ125 X X1 1C3 28199 33 E0 2008 OWNER S SERVICE MANUAL...
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Page 87: ...4 32 WATER PUMP...
Page 131: ...5 30 STEERING 9 Bearing race 2 Refer to removal section Order Part name Q ty Remarks...
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