Yamaha YZF-R125 Service Manual: Checking the piston rings
1. Measure:
Piston ring side clearance
Out of specification 
Replace the
piston
and piston rings as a set.
NOTE:
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings. 
2. Install:
- Piston ring (into the cylinder)
NOTE:
Level the piston ring into the cylinder with the piston crown.
a. 40 mm (1.57 in)
3. Measure:
- Piston ring end gap
Out of specification
Replace
the piston ring.
NOTE:
The oil ring expander spacer end gap cannot be
measured. If the oil ring rail gap is excessive, replace
all three piston rings. 
Checking the cylinder and piston
1. Check:
Piston wall
Cylinder wall
Vertical scratches Replace the
cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
Piston-to-cylinder clearance
a. Mea ...
Checking the piston pin
1. Check:
Piston pin
Blue discoloration/grooves
Replace the
piston pin and then check the lubrication system.
2. Measure:
Piston pin outside diameter "a"
Out of specification ...
Other materials:
Checking the steering
Worn or loose steering bearings may
cause danger. Therefore, the operation
of the steering must be checked as follows
at the intervals specified in the periodic
maintenance and lubrication
chart.
Place a stand under the engine to
raise the front wheel off the
ground. WARNING! To ...
Checking the front wheel
1. Check:
Front wheel axle
Roll the wheel axle on a flat surface.
Bends → Replace.
WARNINGDo not attempt to straighten a bent wheel
axle.
2. Check:
Tire
Front wheel
Damage/wear → Replace.
Refer to "CHECKING THE TIRES" on page
3-23 and "CHECKING TH ...
Checking the valve springs
The following procedure applies to all of the
valve springs.
1. Measure:
Valve spring free length "a"
Out of specification Replace the valve
spring.
2. Measure:
Compressed valve spring force "a"
Out of specification Replace the valve
spring.
b. Installed length
3. ...