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:

    Disassembling the front wheel
    1. Remove: Oil seal Wheel bearings a. Clean the surface of the front wheel hub. b. Remove the oil seal "1" with a flat-head screwdriver. NOTE: To prevent damaging the wheel, place a rag "2" between the screwdriver and the wheel surface. c. Remove the wheel bearings "3" with a ge ...

    Checking and lubricating the sidestand
    Checking and lubricating the sidestand The operation of the sidestand should be checked before each ride, and the sidestand pivot and metal-to-metal contact surfaces should be lubricated if necessary. WARNING If the sidestand does not move up and down smoothly, have a Yamaha deal ...

    Troubleshooting
    Any of the following fail to light: headlight, high beam indicator light, taillight, license plate light, auxiliary light or meter light. NOTE: Before troubleshooting, remove the following part(s): 1. Seats 2. Fuel tank ...

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