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:
Adjusting the exhaust gas volume
NOTE:
Be sure to set the CO density level to standard,
and then adjust the exhaust gas volume.
1. Remove:
Rider seat
Refer to "GENERAL CHASSIS" on page 4-1.
2. Set the main switch to "OFF".
3. Disconnect:
Self-diagnosis signal connector "1"
4. Connect:
FI diagnostic tool "2 ...
General information
NOTICEThis manual was produced by MBK Industrie.
primarily for use by Yamaha dealers and their qualified
mechanics. It is not possible to include all the knowledge of a mechanic
in one manual. Therefore, anyone
who uses this book to perform maintenance and repairs on Yamaha vehi ...
Removing the front fork legs
The following procedure applies to both of the
front fork legs.
1. Stand the vehicle on a level surface.
WARNINGSecurely support the vehicle so that there
is
no danger of it falling over.
2. Loosen:
Handlebar pinch bolt "1"
Handlebar bolt "2"
Upper bracket ...