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:
Removing the front brake caliper
NOTE:
Before disassembling the brake caliper, drain
the brake fluid from the entire brake system.
1. Remove:
Brake hose union bolt "1"
Copper washers "2"
Brake hose "3"
NOTE:
Put the end of the brake hose into a container
and pump out the brake fluid carefully.
...
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 spark plug cap
1. Check:
Spark plug cap resistance
Out of specification Replace.
a. Remove the spark plug cap from the spark
plug lead.
b. Connect the pocket tester ( × 1k)
to the
spark plug cap as shown.
c. Measure the spark plug cap resistance. ...