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 ...

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    Throttle position sensor
    1. Check: Throttle position sensor a. Connect the digital circuit tester to the terminals of the throttle body sensor assembly coupler as shown. Positive tester probe → gray/red terminal "1" Negative tester probe → gray/black terminal "2" b. Measure the throttle pos ...

    Checking and lubricating the cables
    The operation of all control cables and the condition of the cables should be checked before each ride, and the cables and cable ends should be lubricated if necessary. If a cable is damaged or does not move smoothly, have a Yamaha dealer check or replace it. WARNING! Damage to the out ...

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