Yamaha YZF-R125 Service Manual: Lubricating the drive chain
The drive chain consists of many interacting parts. If the drive chain is not maintained properly, it will wear out quickly. Therefore, the drive chain should be serviced, especially when the vehicle is used in dusty areas.
This vehicle has a drive chain with small rubber O-rings between each side plate. Steam cleaning, high-pressure washing, certain solvents, and the use of a coarse brush can damage these O-rings. Therefore, use only kerosene to clean the drive chain. Wipe the drive chain dry and thoroughly lubricate it with engine oil or chain lubricant that is suitable for O-ring chains.
Do not use any other lubricants on the drive
chain since they may contain solvents that could
damage the O-rings. 
Adjusting the drive chain slack
NOTE:
The drive chain slack must be checked at the
tightest point on the chain.
CAUTION:A drive chain that is too tight will
overload
the engine and other vital parts, and one that
...
Checking and adjusting the steering head
1. Stand the vehicle on a level surface
WARNINGSecurely support the vehicle so that there
is
no danger of it falling over.
NOTE:
Place the vehicle on a suitable stand so that the ...
Other materials:
Checking the clutch springs
The following procedure applies to all of the
clutch springs.
1. Check:
Clutch spring
Damage Replace the clutch
springs as a
set.
2. Measure:
Clutch spring free length "a"
Out of specification Replace
the clutch
springs as a set.
...
Checking the drive chain
1. Measure:
15-link section "a" of the drive chain
Out of specification Replace the drive
chain.
a. Measure the length "a" between the inner
sides of the pins and the length "b" between
the outer sides of the pins on a 15-link section
of the drive chain as shown in the illustration.
...
Disassembling the rear brake caliper
1. Remove:
Brake caliper piston "1"
Brake caliper piston dust seal "2"
Brake caliper piston seal "3"
a. Blow compressed air into the brake hose joint
opening "a" to force out the piston from the
brake caliper.
WARNING
Cover the brake caliper piston with a rag.
Be careful no ...