Yamaha YZF-R125 Service Manual: 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 opening pressure
Below the specified pressure
Replace the radiator cap.
a. Install the radiator cap tester "1" and radiator
cap tester adapter "2" to the radiator cap "3".
b. Apply the specified pressure for ten seconds and make sure there is no drop in pressure.
4. Check:
- Radiator fan
Damage
Replace.
Malfunction
Check and repair.Refer to "COOLING SYSTEM" on page 8-25.
Radiator
...
Installing the radiator
1. Fill:
Cooling system
(with the specified amount of the recommended
coolant)
Refer to "CHANGING THE COOLANT" on
page 3-15.
2. Check:
Cooling system
Leaks Repair or replace any
...
Other materials:
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
...
Installing the thermostat
1. Install:
Thermostat
NOTE:
Install the thermostat with its breather hole "a"
facing up.
2. Install:
Copper washer
Coolant temperature sensor
CAUTION:Use extreme care when handling the
coolant
temperature sensor. Replace any part that
was dropped or subjected to ...
Installing the exhaust assembly
1. Install:
Exhaust assembly "1"
Exhaust pipe nuts "2"
Exhaust assembly bolts "3" "4"
NOTE:
Do not fully tighten the nuts and bolts.
2. Tighten:
Exhaust pipe nuts "2"
Exhaust assembly bolt "4"
Exhaust assembly bolt "3"
...