Yamaha YZF-R125 Service Manual: 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
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.
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 piston pin
1. Check:
Piston pin
Blue discoloration/grooves
Replace the
piston pin and then check the lubrication system.
2. Measure:
Piston pin outside diameter "a"
Out of specification Replace
the piston pin.
3. Measure:
Piston pin bore diameter "b"
Out of specifica ...
Installing the water pump
1. Install:
Water pump assembly "1"
O-rings "2"
NOTE:
Align the projection "a" on the impeller shaft
with the slit "b" on the camshaft sprocket bolt.
Lubricate the O-rings with a thin coat of lithiumsoap-
based grease.
2. Fill:
Cooling system
(with the specified amou ...
Engine tightening torques
Cylinder head tightening sequence:
Generator cover tightening sequence:
Clutch cover tightening sequence:
Crankcase tightening sequence:
A. Left crankcase
B. Right crankcase ...