Yamaha Wr250r 2008 Manual

							 
CYLINDER AND PISTON 
5-27 
d. If out of specification, replace the cylinder,
piston and piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
piston and piston rings as a set.

 
EAS24430 
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 cylinder)
NOTE:
 
Level the piston ring into the cylinder with the 
piston crown.
3. Measure: 
 
Piston ring end gap
Out of specification   
→  
 Replace the piston
ring.
NOTE:
 
The oil ring expander spacer’s end gap cannot
be measured. If the oil ring rail’s gap is exces- 
sive, replace all three piston rings. 
EAS24440 
CHECKING THE PISTON PIN 
1. Check: 
 
Piston pin
Blue discoloration/grooves   
→  
 Replace the
piston pin and then check the lubrication sys-
tem.
2. Measure: 
 
Piston pin outside diameter “a”
Out of specification  
→  
 Replace the piston pin.  
Piston-to-cylinder clearance =
Cylinder bore  
“ 
D 
” 
 -
Piston skirt diameter  
“ 
P 
” 
Piston-to-cylinder clearance
0.010 
– 
0.035 mm (0.0004 
– 
0.0014
in)
Limit
0.10 mm (0.0039 in)
Piston ring side clearance
Top ring side clearance (installed)
0.030 
– 
0.065 mm (0.0012 
– 
0.0026
in)
Limit
0.115 mm (0.0045 in)
Second ring side clearance (in-
stalled)
0.020 
– 
0.055 mm (0.0008 
– 
0.0022
in)
Limit
0.115 mm (0.0045 in) 
a. 40 mm (1.57 in) 
Piston ring end gap
Top ring
End gap (installed)
0.15 
– 
0.25 mm (0.0059 
–  
0.0098 in)
Limit
0.50 mm (0.020 in)
2nd ring
End gap (installed)
0.30 
– 
0.45 mm (0.0118 
–  
0.0177 in)
Limit
0.80 mm (0.031 in)
Oil ring
End gap (installed)
0.10 
– 
0.40 mm (0.0039 
–  
0.0157 in) 
						

							 
CYLINDER AND PISTON 
5-28 
3. Measure: 
 
Piston pin bore diameter “b”
Out of specification  
→ 
 Replace the piston.
4. Calculate: 
 
Piston-pin-to-piston-pin-bore clearance
Out of specification  
→ 
 Replace the piston pin
and piston as a set. 
EAS24450 
INSTALLING THE PISTON AND CYLINDER  
1. Install: 
 
Top ring “1” 
 
2nd ring “2” 
 
Lower oil ring rail “3” 
 
Upper oil ring rail “4” 
 
Oil ring expander “5”
NOTE:
 
Be sure to install the piston rings so that the 
manufacturer’s marks or numbers face up.
2. Install: 
 
Cylinder gasket 
 
Water pipe “1” 
 
Dowel pins “2” 
 
O-ring “3”
3. Install: 
 
Piston “1” 
 
Piston pin “2” 
 
Piston pin clips “3” 
NOTE:
 
 
Apply engine oil the piston pin. 
 
Make sure the mark “a” on the piston points to-
wards the exhaust side of the cylinder. 
 
Before installing the piston pin clip, cover the
crankcase opening with a clean rag to prevent 
the clip from falling into the crankcase. 
Piston pin outside diameter
16.991 
– 
17.000 mm 
(0.6689 
– 
0.6693 in)
Limit
16.971 mm (0.668 in)
Piston pin bore inside diameter
17.002 
– 
17.013 mm 
(0.6694 
– 
0.6698 in)
Limit
17.043 mm (0.670 in)
Piston-pin-to-piston-pin-bore clearance
=
Piston pin bore diameter  
“ 
b 
” 
 -
Piston pin outside diameter  
“ 
a 
” 
Piston pin/piston pin hole clear-
ance
0.002 
– 
0.022 mm 
(0.00008 
– 
0.00087 in)
b
New
New
New 
						

							 
CYLINDER AND PISTON 
5-29 
4. Lubricate: 
 
Piston 
 
Piston rings 
 
Cylinder
(with the recommended lubricant)
5. Offset: 
 
Piston ring end gaps
6. Install: 
 
Cylinder
NOTE:
 
 
While compressing the piston rings with one
hand, install the cylinder with the other hand. 
 
Pass the timing chain and timing chain guide 
(exhaust side) through the timing chain cavity. 
Recommended lubricant
Engine oil 
a. Top ring
b. Upper oil ring rail
c. Oil ring expander
d. Lower oil ring rail
e. 2nd ring
f. 20 mm 
Cylinder bolt
10 Nm (1.0 m•kg, 7.2 ft•lb)
1
23
New a
TR.. 
						

							 
STARTER MOTOR 
5-30 
EAS24780 
STARTER MOTOR 
Removing the starter motor
Order Job/Parts to remove Q’ty Remarks  
Seat/Air scoop (left/ritht)Refer to “GENERAL CHASSIS” on page 
4-1.
EXUP cable/Exhaust pipe/Muffler Refer to “ENGINE REMOVAL” on page 5-1.
1 Starter motor lead 1 Disconnect.
2 Starter motor 1
For assembly, reverse the disassembly pro-
cedure.
1
2T R..5 Nm (0.5 m • kg, 3.6 ft • Ib) T R..10 Nm (1.0 m • kg, 7.2 ft • Ib)  
						

							 
STARTER MOTOR 
5-31 
Disassembling the starter motor
Order Job/Parts to remove Q’ty Remarks  
1 Starter motor front cover 1
2 Lock washer 1
3 Armature assembly 1
4 Starter motor yoke 1
5 Starter motor rear cover 1
6 Brush holder set 1
For assembly, reverse the disassembly pro-
cedure.
1 2 34 5
6 
						

							 
STARTER MOTOR 
5-32 
EAS24790 
CHECKING THE STARTER MOTOR 
1. Check: 
 
Commutator
Dirt  
→ 
 Clean with 600 grit sandpaper.
2. Measure: 
 
Commutator diameter “1”
Out of specification  
→ 
 Replace the starter
motor.
3. Measure: 
 
Mica undercut “a”
Out of specification  
→ 
 Scrape the mica to the
proper measurement with a hacksaw blade
that has been grounded to fit the commuta-
tor.
NOTE:
 
The mica of the commutator must be undercut to 
ensure proper operation of the commutator.
4. Measure: 
 
Armature assembly resistances (commutator
and insulation)
Out of specification  
→ 
 Replace the starter
motor.

 
a. Measure the armature assembly resistances
with the pocket tester.b. If any resistance is out of specification, re-
place the starter motor.

 
5. Measure: 
 
Brush length “a”
Out of specification   
→  
 Replace the brushes
as a set.
6. Measure: 
 
Brush spring force
Out of specification  
→  
 Replace the brush
springs as a set. 
Limit
27.0 mm (1.06 in)
Mica undercut (depth)
0.70 mm (0.03 in) 
Pocket tester
90890-03112
Analog pocket tester
YU-03112-C
Armature coil
Commutator resistance “1”
0.004  
–  
0.005   
Ω  
 at 20  
°  
C (68  
°  
F)
Insulation resistance “2”
Above 1 M  
Ω  
 at 20  
°  
C (68  
°  
F)
Limit
3.50 mm (0.14 in)
Brush spring force
7.16 
–  
9.52 N (25.77  
–  
34.27 oz)
(730 
– 
971 gf) 
						

							 
STARTER MOTOR 
5-33 
7. Check: 
 
Gear teeth
Damage/wear  
→ 
 Replace the gear.
8. Check: 
 
Bearing 
 
Oil seal
Damage/wear  
→ 
 Replace the defective part
(s). 
EAS24800 
ASSEMBLING THE STARTER MOTOR 
1. Install: 
 
Brush holder “1”
NOTE:
 
Align the tab on the brush seat with the slot in the 
starter motor rear cover “2”.
2. Install: 
 
Thrust support “1”
NOTE:
 
Align the tab of thrust support with the slot of sta- 
tor motor front cover “2”.
3. Install: 
 
Starter motor yoke “1” 
 
Starter motor front cover “2” 
 
Starter motor rear cover “3”
NOTE:
 
Align the match marks on the starter motor yoke
with the match marks on the starter motor front 
cover “a” and starter motor rear cover “b”.
1 2
1
2
1 32
a b 
						

							 
CLUTCH 
5-34 
EAS25061 
CLUTCH 
Removing the clutch cover
Order Job/Parts to remove Q’ty Remarks  
Drain the engine oilRefer to “CHANGING THE ENGINE OIL” on 
page 3-11.
Drain the coolantRefer to “CHANGING THE COOLANT” on 
page 3-18.
1 Brake pedal spring 1 Remove it from the frame mounting hook.
2 Water pump housing cover 1
3 Gasket 1
4 Oil cleaner element cover 1
5 Oil cleaner element 1
6 Cover 1
7 Clutch cover 1Remove the clutch cover only if you do not 
remove the primary drive gear.
8 Clutch cover gasket 1
9 Dowel pin 2
10 Crankcase cover (right) 1
11 Crankcase cover right gascket 1
12 Water pipe 1
13 O-ring 1
14 Dowel pin 2
1
23
45
678
91011
1213 14
14
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib)  
						

							 
CLUTCH 
5-35 
For installation, reverse the removal proce-
dure.  
Removing the clutch cover
Order Job/Parts to remove Q’ty Remarks
1
23
45
678
91011
1213 14
14
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib) 
T R..10 Nm (1.0 m • kg, 7.2 ft • Ib)  
						

							 
CLUTCH 
5-36 
Removing the clutch
Order Job/Parts to remove Q’ty Remarks  
1 Clutch spring 5
2 Pressure plate 1
3 Push rod 1
4 Locknut 1
5 Friction plate 7
6 Clutch plate 6
7 Primary drive gear nut 1
8 Lock washer 1
9 Clutch boss nut 1
10 Lock washer 1
11 Clutch boss 1
12 Thrust washer 1
13 Clutch housing 1
14 Ball 1
15 Clutch push rod 1
16 Primary drive gear 1
For installation, reverse the removal proce-
dure.
23
4
5 (5)1(5)
6
78 910111213 1415
16
E
E
T R..8 Nm (0.8 m • kg, 5.8 ft • Ib) 
T R..8 Nm (0.8 m • kg, 5.8 ft • Ib) 
T R..80 Nm (8.0 m • kg, 58 ft • Ib) 
T R..75 Nm (7.5 m • kg, 54 ft • Ib) 
E