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:
Rear wheel
To remove the rear wheel
WARNING
To avoid injury, securely support the
vehicle so there is no danger of it
falling over.
Loosen the axle nut.
Axle nut
Drive chain slack adjusting bolt
Locknut
Brake caliper
Lift the rear wheel off the ground
according to the pr ...
Drive chain slack
The drive chain slack should be
checked before each ride and adjusted
if necessary.
To check the drive chain slack
Place the motorcycle on the sidestand.
TIP
When checking and adjusting the drive
chain slack, there should be no weight
on the motorcycle.
Shift the transmission in ...
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 compression
stroke, align the "I" mark "c" on the camshaft
sprocket with the mark "d" on the
cylinder h ...