Yamaha YZF-R125 Service Manual: Adjusting the valve clearance

The following procedure applies to all of the valves.

NOTE:

  • Valve clearance adjustment should be made on a cold engine, at room temperature.
  • When the valve clearance is to be measured or adjusted, the piston must be at top dead center (TDC) on the compression stroke.

1. Remove:

  • Bottom cowling Refer to "GENERAL CHASSIS" on page 4-1.
  • Fuel tank Refer to "FUEL TANK" on page 7-1.

2. Disconnect:

  • Spark plug cap

3. Remove:

  • Spark plug
  • Ignition coil "1"
  • Plastic locking tie "2"

4. Disconnect:

  • Main switch coupler "3"
  • Left handlebar switch couplers "4"

Adjusting the valve clearance


  • Cylinder head cover
  • Cylinder head cover gasket Refer to "CYLINDER HEAD" on page 5-7.

NOTE:

When removing the cylinder head cover, lift it out from between the frame tubes.

5. Remove:

  • Timing mark accessing screw "1"
  • Crankshaft end accessing screw "2"

Adjusting the valve clearance


6. Measure:

  • Valve clearance Out of specification → Adjust.

a. Turn the crankshaft counterclockwise.

b. Align the TDC mark "a" on the generator rotor with the stationary pointer "b" on the generator cover.

Adjusting the valve clearance


c. Check that the cam lobes are positioned as shown in the illustration.

Adjusting the valve clearance


d. Measure the valve clearance with a thickness gauge "1".

Out of specification → Adjust.

Adjusting the valve clearance


7. Adjust: - Valve clearance

a. Loosen the locknut "1".

b. Insert a thickness gauge "2" between the end of the adjusting screw and the valve tip.

Adjusting the valve clearance


c. Turn the adjusting screw "3" in direction "a" or "b" until the specified valve clearance is obtained.

Adjusting the valve clearance



  • Hold the adjusting screw to prevent it from moving and tighten the locknut to specification.

d. Measure the valve clearance again.

e. If the valve clearance is still out of specification, repeat all of the valve clearance adjustment steps until the specified clearance is obtained.

8. Install:

  • Crankshaft end accessing screw (along with the O-ring )

  • Timing mark accessing screw (along with the O-ring   )

9. Install:

  • Cylinder head cover gasket

  • Cylinder head cover
  • Spark plug Refer to "CYLINDER HEAD" on page 5-7.

10.Connect:

  • Left handlebar switch couplers "1"
  • Main switch coupler "2"

11.Install:

  • Plastic locking tie "3"

NOTE:

Fasten the wire harness (to horn), wire harness (to left handlebar switch), front brake light switch lead, right handlebar switch lead, and main switch lead to the frame with a plastic locking tie.

Refer to "CABLE ROUTING" on page 2-33.

12.Install:

  • Ignition coil "4"

  • Spark plug

Adjusting the valve clearance


13.Connect:

  • Spark plug cap

14.Install:

  • Fuel tank Refer to "FUEL TANK" on page 7-1.
  • Bottom cowling Refer to "GENERAL CHASSIS" on page 4-1.
    Engine
    ...

    Adjusting the exhaust gas volume
    NOTE: Be sure to set the CO density level to standard, and then adjust the exhaust gas volume. 1. Remove: Rider seat Refer to "GENERAL CHASSIS" on page 4-1. 2. Set the main switch to "OFF" ...

    Other materials:

    Installing the generator
    1. Install: Woodruff key Generator rotor Washer Generator rotor nut NOTE: Clean the tapered portion of the crankshaft and the generator rotor hub. When installing the generator rotor, make sure the woodruff key is properly sealed in the keyway of the crankshaft. 2. Tighte ...

    Checking the cylinder head
    1. Eliminate: Combustion chamber carbon deposits (with a rounded scraper) NOTE: Do not use a sharp instrument to avoid damaging or scratching: Spark plug bore threads Valve seats 2. Check: Cylinder head Damage/scratches   Replace. Cylinder head water jacket Min ...

    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 from the piston ring grooves and piston rings. 2. Install: Piston ring (into the cylind ...

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