Yamaha YFM250XL(C) Service Manual page 219

FINAL DRIVE GEAR AND DRIVE SHAFT
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Example:
1) If the "+01" is stamped on the final
drive pinion gear,
a = 79 + 0.01 = 79.01
2) If the "50" is stamped on the final gear
case,
b = 78 + 0.50 = 78.50
3) Therefore, "A" is,
"A" = 79.01 – 78.50 = 0.51 mm
4) Round off hundredths digit and select
appropriate shim(s).
In the example above, the calculated
number is 0.51. The chart instructs you
to round off 1 to 0 at the hundredth
place.
Thus, the shim thickness is 0.50 mm.
Hundredths
0, 1, 2
3, 4, 5, 6, 7
8, 9
Shim sizes are supplied in the following
thickness.
Final drive pinion
gear shim
0.15
Thickness (mm) 0.30
0.40
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Ring gear shim(s) selection
1.Select:
Ring gear shim(s) 1
DRIV
Round value
0
5
10
0.50
0.60
6