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 cylinder head breather hose
    1. Remove: Left side panel Refer to "GENERAL CHASSIS" on page 4-1. 2. Check: Cylinder head breather hose "1" Cracks/damage → Replace. Loose connection → Connect properly. CAUTION:Make sure the cylinder head breather hose is routed correctly. ...

    Adjusting the engine idling speed
    The engine idling speed must be checked and, if necessary, adjusted as follows at the intervals specified in the periodic maintenance and lubrication chart. The engine should be warm before making this adjustment. Remove panel A. Check the engine idling speed and, if necessary, ...

    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. ...

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