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:

Installing the steering head
1. Lubricate: Upper bearing Lower bearing Bearing races 2. Install: Lower ring nut Rubber washer Upper ring nut Lock washer Refer to "CHECKING AND ADJUSTING THE STEERING HEAD" on page 3-22. 3. Install: Upper bracket Steering stem nut NOTE: Temporarily tighten t ...

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