Yamaha F20A, Service Manual

Page: 42 / 444

2-4
SPEC
E
MAINTENANCE SPECIFICATIONS
Margin thickness (D)
Intake mm (in) 0.6 ~ 1.0 (0.024 ~ 0.039)
Exhaust mm (in) 0.7 ~ 1.1 (0.026 ~ 0.043)
Stem outside diameter
Intake mm (in) 5.475 ~ 5.490 (0.2155 ~ 0.2161)
Exhaust mm (in) 5.460 ~ 5.475 (0.2150 ~ 0.2155)
Guide inside diameter mm (in) 5.500 ~ 5.512 (0.2147 ~ 0.2170)
Stem-to-guide clearance
Intake mm (in) 0.010 ~ 0.037 (0.0004 ~ 0.0015)
Exhaust mm (in) 0.025 ~ 0.052 (0.0004 ~ 0.0015)
Stem runout limit mm (in) 0.016 (0.0006)
VALVE SPRINGS
Free length mm (in) 37.85 ~ 39.85 (1.491 ~ 1.569)
Free length limit mm (in) 37.85 (1.49)
Tilt limit mm (in) 1.7 (0.06)
PISTON(S)
Piston-to-cylinder clearance mm (in) 0.035 ~ 0.065 (0.0014 ~ 0.0026)
Measuring point (D)
Standard mm (in) 64.950 ~ 64.965 (2.5570 ~ 2.5573)
Oversize mm (in) 65.450 ~ 65.465 (2.5768 ~ 2.5774)
Measuring point (H) mm (in) 2 (0.007)
Pin boss inside diameter mm (in) 15.974 ~ 15.985 (0.6289 ~ 0.6293)
Oversize piston diameter
1st (except for USA) mm (in) + 0.25 (0.001)
2nd mm (in) + 0.50 (0.002)
PISTON PIN(S)
Diameter mm (in) 15.965 ~ 15.970 (0.6285 ~ 0.6287)
PISTON RINGS
Top ring
Type Rounded edge
Dimensions (B
×
T) mm (in) 1.2
×
2.4 (0.047
×
0.094)
End gap (installed) mm (in) 0.15 ~ 0.30 (0.006 ~ 0.012)
Wear limit mm (in) 0.5 (0.020)
Side clearance (installed) mm (in) 0.04 ~ 0.08 (0.002 ~ 0.003)
2nd ring
Type Tapered edge
Dimensions (B
×
T) mm (in) 1.5
×
2.7 (0.591
×
0.106)
End gap (installed) mm (in) 0.30 ~ 0.50 (0.012 ~ 0.020)
Wear limit mm (in) 0.7 (0.028)
Side clearance (installed) mm (in) 0.03 ~ 0.07 (0.001 ~ 0.003)
Oil ring
Dimensions (B
×
T) mm (in) 2.42
×
2.75 (0.095
×
0.108)
End gap (installed) mm (in) 0.20 ~ 0.70 (0.008 ~ 0.028)
Item Unit
Model
Worldwide F20A F25A
USA, CANADA — F25X
H
D
T
B
B
T
B
T