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 coolant level
1. Stand the vehicle on a level surface.
NOTE:
Place the vehicle on a suitable stand.
Make sure the vehicle is upright.
2. Check:
Coolant level
The coolant level should be between the
maximum level mark "a" and minimum level
mark "b".
Below the minimum level mark → Add t ...
Circuit diagram
4. Main fuse
5. Main switch
9. Battery
25.ECU (engine control unit)
36.License plate light
37.Tail/brake light
44.Headlight relay
46.Pass switch
47.Dimmer switch
51.Headlight (low beam)
52.Auxiliary light
54.Headlight (high beam)
58.Meter light
60.High beam indicator light
64.Ignit ...
Checking the fid (fast idle solenoid)
1. Disconnect:
FID (fast idle solenoid) coupler
2. Check:
FID (fast idle solenoid) resistance
a. Disconnect the FID (fast idle solenoid) coupler
from the FID.
b. Connect the pocket tester ( × 10)
to the terminals
of the FID (fast idle solenoid).
Positive tester probe ...