Yamaha YZF-R125 Service Manual: 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. Measure cylinder bore "C" with the cylinder bore gauge.
NOTE:
Measure cylinder bore "C" by taking side-to-side and front-to-back measurements of the cylinder.
Then, find the average of the measurements.
b. If out of specification, replace the cylinder, and replace the piston and piston rings as a set.
c. Measure piston skirt diameter D "a" with the micrometer.
b. 5.0 mm (0.20 in) from the bottom edge of the
piston 
d. If out of specification, replace the piston and piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula. 
f. If out of specification, replace the cylinder, and replace the piston and piston rings as a set.
Removing the piston
1. Remove:
Piston pin clips "1"
Piston pin "2"
Piston "3"
CAUTION:Do not use a hammer to drive the piston
pin
out.
NOTE:
Before removing the piston pin c ...
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 ...
Other materials:
Checking the relays
Check each switch for continuity with the pocket
tester. If the continuity reading is incorrect, replace
the relay.
1. Disconnect the relay from the wire harness.
2. Connect the pocket tester ( × 1) and battery
(12 V) to the relay terminal as shown.
Check the relay operation.
Out ...
Multi-function display
1. Multi-function display
2. "RESET/SELECT" button
The multi-function display is equipped with the
following:
a speedometer (which shows the riding speed)
an odometer (which shows the total distance
traveled)
two tripmeters (which show the distance traveled
since they were last ...
Avoid Carbon Monoxide Poisoning
All engine exhaust contains carbon
monoxide, a deadly gas. Breathing carbon
monoxide can cause headaches,
dizziness, drowsiness, nausea, confusion,
and eventually death.
Carbon Monoxide is a colorless, odorless,
tasteless gas which may be
present even if you do not see or smell
any en ...