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 shift shaft
1. Install: Stopper lever "1" Stopper lever spring "2" NOTE: Install the stopper lever spring as shown in the illustration. Hook the ends of the stopper lever spring onto the stopper lever and the crankcase boss "3". Mesh the stopper lever with the shift drum segment assembly. ...

Checking the front fork legs
The following procedure applies to both of the front fork legs. 1. Check: Inner tube Outer tube Bends/damage/scratches Replace. WARNINGDo not attempt to straighten a bent inner tube as this may dangerously weaken it. 2. Measure: Spring free length "a" Out of sp ...

Multi-function display
Multi-function display Multi-function display "RESET/SELECT" button WARNING Be sure to stop the vehicle before making any setting changes to the multi-function display. Changing settings while riding can distract the operator and increase the risk of an accident. The multi- ...