Yamaha YZF-R125 Service Manual: Checking the valve seats
The following procedure applies to all of the valves and valve seats.
1. Eliminate:
- Carbon deposits (from the valve face and valve seat)
2. Check:
- Valve seat
Pitting/wear
Replace the
cylinder head.
3. Measure:
- Valve seat width C "a"
Out of specification
Replace
the cylinder head.
a. Apply Mechanic's blueing dye (Dykem) "b" onto the valve face.
b. Install the valve into the cylinder head.
c. Press the valve through the valve guide and onto the valve seat to make a clear impression.
d. Measure the valve seat width.
NOTE:
Where the valve seat and valve face contacted one another, the blueing will have been removed.
4. Lap:
- Valve face
- Valve seat
NOTE:
After replacing the cylinder head or replacing the valve and valve guide, the valve seat and valve face should be lapped.
a. Apply a coarse lapping compound "a" to the valve face.
| CAUTION: Do not let the lapping compound enter the gap between the valve stem and the valve guide. |
b. Apply molybdenum disulfide oil onto the valve stem.
c. Install the valve into the cylinder head.
d. Turn the valve until the valve face and valve seat are evenly polished, then clean off all of the lapping compound.
NOTE:
For the best lapping results, lightly tap the valve seat while rotating the valve back and forth between your hands.
e. Apply a fine lapping compound to the valve face and repeat the above steps.
f. After every lapping procedure, be sure to clean off all of the lapping compound from the valve face and valve seat.
g. Apply Mechanic's blueing dye (Dykem) "b" onto the valve face.
h. Install the valve into the cylinder head.
i. Press the valve through the valve guide and onto the valve seat to make a clear impression.
j. Measure the valve seat width "c" again. If the valve seat width is out of specification, reface and lap the valve seat.
Checking the valves and valve guides
The following procedure applies to all of the
valves and valve guides.
1. Measure:
Valve-stem-to-valve-guide clearance
Out of specification Replace the
valve
guide.
Valve-stem-to-valve ...
Checking the valve springs
The following procedure applies to all of the
valve springs.
1. Measure:
Valve spring free length "a"
Out of specification Replace the valve
spring.
2. Measure:
Compressed valve ...
Other materials:
Checking the transmission
1. Measure:
Main axle runout
(with a centering device and dial gauge "1")
Out of specification Replace
the main axle.
2. Measure:
Drive axle runout
(with a centering device and dial gauge "1")
Out of specification Replace
the drive axle.
3. Check:
Transmiss ...
Checking the engine oil level
1. Stand the vehicle on a level surface.
NOTE:
Place the vehicle on a suitable stand.
Make sure the vehicle is upright.
2. Start the engine, warm it up for several minutes,
and then turn it off.
3. Check:
Engine oil level
The engine oil level should be between the
minimum level ...
Checking the stator coil
1. Disconnect:
Stator coil coupler
(from the wire harness)
2. Check:
Stator coil resistance
Out of specification → Replace the
crankshaft
position sensor/stator assembly.
a. Connect the pocket tester ( ×
1) to the stator
coil coupler as shown.
b. Measure the sta ...