Yamaha YZF-R125 Service Manual: Checking the cylinder head

Yamaha YZF-R125 Service Manual / Engine / Cylinder head / 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

Checking the cylinder head


2. Check:

  • Cylinder head Damage/scratches   Replace.

  • Cylinder head water jacket Mineral deposits/rust
    Eliminate.

3. Measure:

  • Cylinder head warpage Out of specification Resurface
    the cylinder head.

a. Place a straightedge "1" and a thickness gauge "2" across the cylinder head.

Checking the cylinder head


b. Measure the warpage.

c. If the limit is exceeded, resurface the cylinder head as follows.

d. Place a 400-600 grit wet sandpaper on the surface plate and resurface the cylinder head using a figure-eight sanding pattern.

NOTE:

To ensure an even surface, rotate the cylinder head several times.

    Removing the cylinder head
    1. Align: "I" mark "a" on the generator rotor (with the stationary pointer "b" on the generator cover) a. Turn the crankshaft counterclockwise. b. When the piston is at TDC on the compre ...

    Checking the camshaft sprocket and timing chain guide
    1. Check: Camshaft sprocket More than 1/4 tooth wear "a" Replace the camshaft sprocket, timing chain and crankshaft as a set. a. 1/4 tooth b. Correct 1. Timing chain roller 2. C ...

    Other materials:

    Checking the shift shaft
    1. Check: Shift shaft Bends/damage/wear Replace. Shift shaft spring Damage/wear Replace. Checking the stopper lever 1. Check: Stopper lever Bends/damage Replace. Roller turns roughly Replace the stopper lever. Stopper lever spring Damage/wear Replace. ...

    Installing the drive chain
    1. Lubricate: Drive chain Master link 2. Install: Drive sprocket Drive sprocket retainer bolts 3. Install: Master link O-rings Master link plate Master link clip "1" CAUTION: The closed end of the master link clip must face in the direction of drive ch ...

    Replacing the front brake pads
    NOTE: When replacing the brake pads, it is not necessary to disconnect the brake hose or disassemble the brake caliper. 1. Measure: Brake pad wear limit "a" Out of specification Replace the brake pads as a set. 2. Install: Brake pad support Brake pad spring Brake pads ...

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