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:
Rear wheel
To remove the rear wheel
WARNING
To avoid injury, securely support the
vehicle so there is no danger of it
falling over.
Loosen the axle nut.
Axle nut
Drive chain slack adjusting bolt
Locknut
Brake caliper
Lift the rear wheel off the ground
according to the pr ...
Overheating
Engine
1. Clogged coolant passages
Cylinder head and piston
Heavy carbon buildup
2. Engine oil
Incorrect oil level
Incorrect oil viscosity
Inferior oil quality
Cooling system
1. Coolant
Low coolant level
2. Radiator
Damaged or leaking radiator
Faulty radiator cap
...
Faulty lighting or signaling system
Headlight does not come on
- Wrong headlight bulb
- Too many electrical accessories
- Hard charging
- Incorrect connection
- Improperly grounded circuit
- Poor contacts (main or light switch)
- Burnt-out headlight bulb
Headlight bulb burnt out
- Wrong headlight bulb
- Faulty battery
- Fau ...