Yamaha WR250F Owner's Service Manual

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Contents

5-59CRANKCASE AND CRANKSHAFTDISASSEMBLING THECRANKCASE1. Separate:• Right crankcase• Left crankcaseSeparation steps:a. Remove the crankcase bolts "1",hose guide "2" and clutch cableholder "3".Loosen each bolt 1/4 of a turn at atime and after all the bolts are loos-ened, remove them.b. Remove the right crankcase "4".• Place the crankcase with its leftside downward and split it by insert-ing a screwdriver tip into the split-ting slit "a" in the crankcase.• Lift the right crankcase horizontallywhile lightly patting the case split-ting slit and engine mounting bossusing a soft hammer, and leave thecrankshaft and transmission withthe left crankcase.Use soft hammer to tap on thecase half. Tap only on reinforcedportions of case. Do not tap ongasket mating surface. Work slow-ly and carefully. Make sure thecase halves separate evenly. If thecases do not separate, check for aremaining case bolt or fitting. Donot force.c. Remove the dowel pins and O-ring.REMOVING THE CRANKSHAFT1. Remove:• Crankshaft "1"Use the crankcase separatingtool "2".Do not use a hammer to drive outthe crankshaft.REMOVING THE CRANKCASEBEARING1. Remove:• Bearing "1"• Remove the bearing from thecrankcase by pressing its innerrace.• Do not use the removed bearing.CHECKING THE TIMING CHAINAND TIMING CHAIN GUIDE1. Inspect:• Timing chainCracks/stiff → Replace the timingchain and camshaft sprocket as aset.2. Inspect:• Timing chain guideWear/damage → Replace.CHECKING THE CRANKCASE1. Inspect:• Contacting surface "a"Scratches → Replace.• Engine mounting boss "b", crank-caseCracks/damage → Replace.2. Inspect:• BearingRotate inner race with a finger.Rough spot/seizure → Replace.3. Inspect:• Oil sealDamage → Replace.CHECKING THE CRANKSHAFT1. Measure:• Runout limit "a"• Small end free play limit "b"• Connecting rod big end sideclearance "c"• Crank width "d"Out of specification → Replace.Use the dial gauge and a thick-ness gauge.Crankcase separatingtool:YU-1135-A/90890-01135Dial gauge and stand:YU-3097/90890-01252Standard Runout lim-it:0.03 mm (0.0012in)0.05mm(0.002in)Smallendfreeplay:0.4–1.0 mm(0.016–0.039 in)2.0 mm(0.08 in)Sideclear-ance:0.15–0.45 mm(0.0059–0.0177in)0.50mm(0.02 in)Crackwidth:55.95–56.00mm (2.203–2.205 in)—