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Harley-Davidson U-Series Engine Displacement

To use this Chart

1.

Find your bore size in Column 1.

2.

Move right to Column 2 to the exact size for boring (decimal) 

3.

Select your stroke in Columns 3 through 8

Bore,

Relative

Bore,

Absolute

4-9/32"††

4.28125

4-1/2"‡

4.500

4-5/8"‡

4.625

4-3/4"‡

4.750

5"‡

5.000

5-1/4"‡‡

5.250

 Std.*

3.3125"

73.79

77.56

79.72

81.87

86.18

90.49

+.010

3.3225

74.24

78.03

80.20

82.37

86.70

91.04

  .020

3.3325

74.68

78.50

80.68

82.86

87.22

91.58

.030

3.3425

75.13

78.97

81.17

83.36

87.75

92.13

.040

3.3525

75.58

79.45

81.65

83.86

88.27

92.69

.050

3.3625

76.04

79.92

82.14

84.36

88.8

93.24

.060

3.3725

76.49

80.40

82.63

84.86

89.33

93.80

.070

3.3825

76.94

80.87

83.12

85.37

89.86

94.35

.080

3.3925

77.40

81.35

83.61

85.87

90.39

94.91

.090

3.4025

77.86

81.83

84.11

86.38

90.93

95.47

.100**

3.4125

78.31

82.31

84.6

86.89

91.46

96.03

 Std.+

3.421875

78.74

82.77

85.07

87.37

91.96

96.56

 Std. repro++

3.4375

79.46

83.53

85.85

88.17

92.81

97.45

.010†

3.4475

79.93

84.01

86.35

88.68

93.35

98.01

.020

3.4575

80.39

84.50

86.85

89.19

93.89

98.58

.030

3.4675

80.86

84.99

87.35

89.71

94.43

99.15

.040

3.4775

81.33

85.48

87.85

90.23

94.98

99.73

.050

3.4875

81.79

85.97

88.36

90.75

95.53

100.30

.060

3.4975

82.26

86.47

88.87

91.27

96.07

100.88

.070

3.5075

82.73

86.96

89.38

91.79

96.62

101.46

Notes

*

Std. bore 3-5/16" 1937-48 U/UL 11-fin cylinders; also 1936-52 E, EL

**

Largest commercially-available piston oversize (based on 3-5/16")

+

Std. bore 3-27/64" 1937-41 UH/ULH 13-fin cylinders; also 1930-36 V-Series

++

Std. bore 3-7/16" of reproduction 80" pistons; +.0155" over original bore size

† 

Add .0155" to this size to get the actual oversize based on the original

UH/ULH bore (see ++, above)

†† 

Std. stroke 1937-48 all U-Series

Available from KNS Cycle, S&S, Truett & Osborne

‡‡

Extremely complex construction, not practical

"Harley-Davidson" name for reference purposes only. Not affiliated with Harley-Davidson Motor Co.

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