Yamaha MX250 - Page 34

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PERIODIC CHECKS AND ADJUSTMENTS
PERIODIC MAINTENANCE
3.
Pull the recoil starter slowly, and then set the piston at
TDC (top-dead-center) on the compression stroke.
TIP
Check the piston position by inserting a screw driver into
the spark plug hole.
4.
Measure:
• Valve clearance
(Between the rocker arm and valve stem end)
Out of specification  Adjust.
TIP
Valve clearance must be measured when the engine has
cooled down enough to be touched.
5.
Adjust:
• Valve clearance
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Adjustment steps:
a. Loosen the locknut “1” and insert the 0.07 mm
(0.0028 in) thickness gauge between the rocker
arm and the valve tip.
b. Using the tappet adjusting tool “2” turn the adjuster
“3” in or out to obtain the proper valve clearance.
Move the thickness gauge up and down to check for
the proper resistance.
Feeler gauge set:
YU-26900-9
Thickness gauge:
90890-03180
Valve clearance (cold):
Intake: 0.05–0.09 mm (0.0020–0.0035 in)
Exhaust: 0.05–0.09 mm (0.0020–0.0035 in)
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2
Six piece tappet set:
YM-A5970
Tappet adjusting tool:
90890-01311
Feeler gauge set:
YU-26900-9
Thickness gauge:
90890-03180