Yamaha YZF-R125 Service Manual: Checking the piston pin
1. Check:
- Piston pin
Blue discoloration/grooves
Replace the piston pin and then check the lubrication system.
2. Measure:
- Piston pin outside diameter "a"
Out of specification
Replace
the piston pin.
3. Measure:
- Piston pin bore diameter "b"
Out of specification
Replace
the piston.
4. Calculate:
Piston-pin-to-piston-pin-bore clearance
Out of specification 
Replace the
piston pin
and piston as a set.
- Piston-pin-to-piston-pin-bore clearance =
Piston pin bore diameter "b" -
Piston pin outside diameter "a"
Checking the piston rings
1. Measure:
Piston ring side clearance
Out of specification Replace the
piston
and piston rings as a set.
NOTE:
Before measuring the piston ring side clearance,
eliminate any carbon deposits ...
Installing the piston and cylinder
1. Install:
Top ring "1"
2nd ring "2"
Oil ring expander "3"
Lower oil ring rail "4"
Upper oil ring rail "5"
NOTE:
Be sure to install the piston rings so that the
manufacturer marks or ...
Other materials:
Checking the front fork legs
The following procedure applies to both of the
front fork legs.
1. Check:
Inner tube
Outer tube
Bends/damage/scratches
Replace.
WARNINGDo not attempt to straighten a bent inner
tube as this may dangerously weaken it.
2. Measure:
Spring free length "a"
Out of sp ...
Checking and lubricating the cables
The following procedure applies to all of the inner
and outer cables.
WARNINGDamaged outer cable may cause the cable to
corrode and interfere with its movement. Replace
damaged outer cable and inner cables
as soon as possible.
1. Check:
Outer cable
Damage Replace.
2 ...
Battery
A poorly maintained battery will corrode
and discharge quickly. The electrolyte
level, battery lead connections and
breather hose routing should be
checked before each ride and at the intervals
specified in the periodic maintenance
and lubrication chart.
WARNING
Electrolyte is pois ...