Yamaha YZF-R125 Service Manual: Checking the cylinder and piston

Yamaha YZF-R125 Service Manual / Engine / Cylinder and piston / 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.

Checking the cylinder and piston

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.

Checking the cylinder and piston

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 thermostat
1. Check: Thermostat Does not open at 80.5-83.5 C (176.9-182.3 F) Replace. a. Suspend the thermostat "1" in a container "2" filled with water. b. Slowly heat the water "3". c. Place a thermometer "4" in the water. d. While stirring the water, observe the thermostat and th ...

Checking the diode
1. Check: Diode Out of specification Replace. NOTE: The pocket tester or the analog pocket tester readings are shown in the following table. a. Disconnect the diode from the wire harness. b. Connect the pocket tester ( × 1) to the diode terminals as shown. c. Check the diod ...

Checking and replacing the rear wheel sprocket
1. Check: Rear wheel sprocket More than 1/4 tooth "a" wear Replace the rear wheel sprocket. Bent teeth Replace the rear wheel sprocket. b. Correct 1. Drive chain roller 2. Rear wheel sprocket 2. Replace: Rear wheel sprocket a. Remove the self-locking nuts and the ...