Yamaha YZF-R125 Service Manual: Checking the valves and valve guides

Yamaha YZF-R125 Service Manual / Engine / Valves and valve springs / Checking the valves and valve guides

The following procedure applies to all of the valves and valve guides.

1. Measure:

  • Valve-stem-to-valve-guide clearance Out of specification Replace the
    valve guide.

Valve-stem-to-valve-guide clearance = Valve guide inside diameter "a" - Valve stem diameter "b"


Checking the valves and valve guides


2. Replace:

  • Valve guide

NOTE:

To ease valve guide removal and installation, and to maintain the correct fit, heat the cylinder head to 100 C (212 F) in an oven.

a. Remove the valve guide with the valve guide remover "1".

Checking the valves and valve guides


b. Install the new valve guide with the valve guide installer "2" and valve guide remover "1".


Checking the valves and valve guides


a. Valve guide position

c. After installing the valve guide, bore the valve guide with the valve guide reamer "3" to obtain the proper valve-stem-to-valve-guide clearance.

Checking the valves and valve guides


NOTE:

After replacing the valve guide, reface the valve seat.


3. Eliminate:

  • Carbon deposits (from the valve face and valve seat)

4. Check:

  • Valve face Pitting/wear Grind the valve
    face.
  • Valve stem end Mushroom shape or diameter larger than the body of the valve stem Replace
    the valve.

5. Measure:

  • Valve margin thickness D "a" Out of specification Replace
    the valve.

Checking the valves and valve guides


6. Measure:

  • Valve stem runout Out of specification Replace
    the valve.

NOTE:

  • When installing a new valve, always replace the valve guide.
  • If the valve is removed or replaced, always replace the valve stem seal.

Checking the valves and valve guides


    Removing the valves
    The following procedure applies to all of the valves and related components. NOTE: Before removing the internal parts of the cylinder head (e.g., valves, valve springs, valve seats), make sure th ...

    Checking the valve seats
    The following procedure applies to all of the valves and valve seats. 1. Eliminate: Carbon deposits (from the valve face and valve seat) 2. Check: Valve seat Pitting/wear Replace the ...

    Other materials:

    Checking the transmission
    1. Measure: Main axle runout (with a centering device and dial gauge "1") Out of specification Replace the main axle. 2. Measure: Drive axle runout (with a centering device and dial gauge "1") Out of specification Replace the drive axle. 3. Check: Transmiss ...

    Air induction system
    1. Air induction system hose (air filter case to reed valve assembly) 2. Air induction system reed valve assembly 3. Air induction system hose (reed valve assembly to exhaust pipe) Checking the air induction system Air injection The air induction system burns unburned exhaust gases b ...

    Installing the front wheel (disc)
    1. Install: Front brake disc NOTE: Be sure to install the front brake disc with the arrow mark "a" on the disc facing out. Tighten the brake disc bolts in stages and in a crisscross pattern. 2. Check: Front brake disc Refer to "CHECKING THE FRONT BRAKE DISC" on page 4 ...

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