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:
Installing the rear wheel (disc)
1. Install:
Rear brake disc
NOTE:
Tighten the brake disc bolts in stages and in a
crisscross pattern.
2. Check:
Rear brake disc
Refer to "CHECKING THE REAR BRAKE
DISC" on page 4-33.
3. Lubricate:
Rear wheel axle
Contact surface of rear wheel hub and rear
wheel
Whee ...
Checking the piston rings
1. Measure:
Piston ring side clearance
Out of specification Replace the
piston
and piston rings as a set.
NOTE:
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
2. Install:
Piston ring
(into the cylind ...
Checking the timing chain and timing chain guide
1. Check:
Timing chain
Damage/stiffness Replace the
timing
chain and camshaft sprocket as a set.
2. Check:
Timing chain guide (intake side)
Damage/wear Replace.
Checking the oil strainer
1. Check:
Oil strainer
Damage Replace.
Contaminants Clean with solvent.
...