Yamaha WR250F Owner's Service Manual page 153

DISASSEMBLING THE
CRANKCASE
1. Separate:
• Right crankcase
• Left crankcase
Separation steps:
a. Remove the crankcase bolts "1",
hose guide "2" and clutch cable
holder "3".
Loosen each bolt 1/4 of a turn at a
time and after all the bolts are loos-
ened, remove them.
b. Remove the right crankcase "4".
• Place the crankcase with its left
side downward and split it by insert-
ing a screwdriver tip into the split-
ting slit "a" in the crankcase.
• Lift the right crankcase horizontally
while lightly patting the case split-
ting slit and engine mounting boss
using a soft hammer, and leave the
crankshaft and transmission with
the left crankcase.
Use soft hammer to tap on the
case half. Tap only on reinforced
portions of case. Do not tap on
gasket mating surface. Work slow-
ly and carefully. Make sure the
case halves separate evenly. If the
cases do not separate, check for a
remaining case bolt or fitting. Do
not force.
CRANKCASE AND CRANKSHAFT
c. Remove the dowel pins and O-
ring.
REMOVING THE CRANKSHAFT
1. Remove:
• Crankshaft "1"
Use the crankcase separating
tool "2".
Crankcase separating
tool:
YU-1135-A/90890-
01135
Do not use a hammer to drive out
the crankshaft.
REMOVING THE CRANKCASE
BEARING
1. Remove:
• Bearing "1"
• Remove the bearing from the
crankcase by pressing its inner
race.
• Do not use the removed bearing.
CHECKING THE TIMING CHAIN
AND TIMING CHAIN GUIDE
1. Inspect:
• Timing chain
→
Cracks/stiff Replace the timing
chain and camshaft sprocket as a
set.
2. Inspect:
• Timing chain guide
→
Wear/damage Replace.
5-59
CHECKING THE CRANKCASE
1. Inspect:
• Contacting surface "a"
→
Scratches Replace.
• Engine mounting boss "b", crank-
case
→
Cracks/damage Replace.
2. Inspect:
• Bearing
Rotate inner race with a finger.
→
Rough spot/seizure
3. Inspect:
• Oil seal
→
Damage Replace.
CHECKING THE CRANKSHAFT
1. Measure:
• Runout limit "a"
• Small end free play limit "b"
• Connecting rod big end side
clearance "c"
• Crank width "d"
→
Out of specification
Use the dial gauge and a thick-
ness gauge.
Dial gauge and stand:
YU-3097/90890-01252
Standard
Runo
0.03 mm (0.0012
ut lim-
in)
it:
Small
end 0.4–1.0 mm
free (0.016–0.039 in)
play:
Side 0.15–0.45 mm
clear- (0.0059–0.0177
ance: in)
55.95–56.00
Crack
mm (2.203–
width:
2.205 in)
Replace.
Replace.
<Limit>
0.05
mm
(0.002
in)
2.0 mm
(0.08 in)
0.50
mm
(0.02 in)
—