Yamaha YZF-R125 Service Manual: Installing the shift forks and shift drum assembly
1. Install:
- Shift fork-L "1"
- Shift fork-C "2"
- Shift fork-R "3"
- Shift drum assembly "4"
- Springs
- Shift fork guide bar "5"
NOTE:
The embossed marks on the shift forks should face towards the right side of the engine and be in the following sequence: "R", "C", "L".
2. Check:
Transmission
Rough movement 
Repair.
NOTE:
- Apply engine oil to each gear and bearing thoroughly.
- Before assembling the crankcase, make sure that the transmission is in neutral and that the gears turn freely.
Assembling the main axle and drive axle
1. Install:
Toothed washer "1"
Circlip "2"
NOTE:
Be sure to install the circlip so that its sharp
edge "a" is facing away from the toothed washer
and gear.
Be sure the circlip ends ...
Cooling system
...
Other materials:
Checking the cylinder head breather hose
1. Remove:
Left side panel
Refer to "GENERAL CHASSIS" on page 4-1.
2. Check:
Cylinder head breather hose "1"
Cracks/damage → Replace.
Loose connection → Connect properly.
CAUTION:Make sure the cylinder head
breather hose is
routed correctly.
...
Adjusting the engine idling speed
NOTE:
Prior to adjusting the engine idling speed, the air
filter element should be clean, and the engine
should have adequate compression.
1. Start the engine and let it warm up for several
minutes.
2. Remove:
Rider seat
Refer to "GENERAL CHASSIS" on page 4-1.
3. Lift the fuel tank. ...
Checking the primary drive gear
1. Remove:
Primary drive gear
Refer to "BALANCER GEAR" on page 5-53.
2. Check:
Primary drive gear
Damage/wear Replace the
primary drive
gear and clutch housing as a set.
Excessive noise during operation
Replace
the primary drive gear and clutch housing as
a set
...