Disassembling The Crankcase; Removing The Crankcase Bearing; Checking The Timing Chain, Timing Chain Guide, Oil Strainer; Checking The Crankcase - Yamaha YZ250F Owner's Service Manual

DISASSEMBLING THE CRANKCASE

EAS1SM5279
1. Separate:
• Right crankcase
• Left crankcase
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a. Remove the crankcase bolts.
TIP
Loosen each bolt 1/4 of a turn at a time and af-
ter all the bolts are loosened, remove them.
b. Remove the right crankcase "1".
TIP
• Place the crankcase with its left side down-
ward and split it by inserting a screwdriver tip
into the splitting slit "a" in the crankcase.
• Lift the right crankcase horizontally while light-
ly patting the crankcase splitting slit and the
engine mounting boss using a soft hammer,
and leave the crankshaft and the transmission
with the left crankcase.
ECA33DD041
NOTICE
Use soft hammer to tap on the case half.
Tap only on reinforced portions of case. Do
not tap on gasket mating surface. Work
slowly 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.
c. Remove the dowel pins and O-ring.
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REMOVING THE CRANKCASE BEARING

EAS1SM5280
1. Remove:
• Bearing "1"
TIP
• Remove the bearing from the crankcase by
pressing its inner race.
• Do not use the removed bearing.
CHECKING THE TIMING CHAIN, TIMING
EAS1SM5281
CHAIN GUIDE, OIL STRAINER
1. Check:
• Timing chain
Stiffness  Replace the camshaft sprocket,
timing chain and crankshaft sprocket as a
set.
2. Check:
• Timing chain guide
Damage/wear  Replace

CHECKING THE CRANKCASE

EAS1SM5282
1. Wash:
• Crankcase
TIP
1
• Wash the crankcase in a mild solvent.
• Remove any remaining gasket from the
crankcase mating surface.
2. Check:
• Crankcase
Crack/damage  Replace.
• Oil delivery passages
Obstruction  Blow out with compressed
air.
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CRANKCASE
a