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 oil pump
1. Check:
Oil pump drive gear
Oil pump driven gear
Oil pump housing
Oil pump housing cover
Cracks/damage/wear Replace the
defective
part(s).
2. Measure:
Inner-rotor-to-outer-rotor-tip clearance "a"
Outer-rotor-to-oil-pump-housing clearance
"b"
- Oil-pump-housing-to-inn ...
Checking the shift drum assembly
1. Check:
Shift drum groove
Damage/scratches/wear Replace
the shift
drum assembly.
Shift drum segment "1"
Damage/wear Replace the
shift drum assembly.
Shift drum bearing "2"
Damage/pitting Replace the
shift drum assembly.
...
Checking the radiator
1. Check:
Radiator fins
obstruction clean.
Apply compressed air to the rear of the radiator.
Damage repair or replace.
NOTE:
Straighten any flattened fins with a thin, flat-head
screwdriver.
2. Check:
Radiator hoses
Cracks/damage Replace.
3. Measure:
Radiator cap ...