Yamaha YZF-R125 Service Manual: Checking the starter clutch
1. Check:
- Starter clutch rollers "1"
- Starter clutch spring caps "2"
- Starter clutch springs "3"
Damage/wear 
Replace the starter
clutch
assembly.
2. Check:
- Starter clutch idle gear
- Starter clutch gear Burrs/chips/roughness/wear Replace the defective part(s).
3. Check:
- Starter clutch gear contacting surfaces Damage/pitting/wear Replace the starter clutch gear.
4. Check:
- Starter clutch operation
a. Install the starter clutch gear "1" onto the starter clutch and hold the generator rotor.
b. When turning the starter clutch gear clockwise "A", the starter clutch and the starter clutch gear should engage, otherwise the starter clutch is faulty and must be replaced.
c. When turning the starter clutch gear counterclockwise
"B", it should turn freely, otherwise
the starter clutch is faulty and must be replaced.
Removing the starter clutch
1. Remove:
Starter clutch bolts "1"
NOTE:
While holding the generator rotor "2" with the
sheave holder "3", remove the starter clutch
bolts.
Do not allow the sheave holder to touch th ...
Installing the starter clutch
1. Install:
Starter clutch assembly
Starter clutch bolts "1"
NOTE:
While holding the generator rotor "2" with the
sheave holder "3", tighten the starter clutch
bolts.
Do not allow t ...
Other materials:
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 numbers face up.
2. Install:
Piston "1"
Piston pin "2"
Piston pin clips "3"
NOTE:
...
Checking the spark plug
1. Remove:
Right side cover
Refer to "GENERAL CHASSIS" on page 4-1.
2. Disconnect:
Spark plug cap
3. Remove:
Spark plug
CAUTION:Before removing the spark plug, blow away
any dirt accumulated in the spark plug well
with compressed air to prevent it from falling
...
Installing the drive chain
1. Lubricate:
Drive chain
Master link
2. Install:
Drive sprocket
Drive sprocket retainer bolts
3. Install:
Master link
O-rings
Master link plate
Master link clip "1"
CAUTION:
The closed end of the master link clip must
face in the direction of drive ch ...