Notes gleaned from several sources on OldIHC.org
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Cylinder Compression
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| The following table shows the theoretical compression pressures for the various compression ratios. The pressure is given in pounds per square inch at cranking speed, which is approximately 125 to 150 revolutions of the engine. It’s a lot easier to turn the engine over and get good readings if all of the spartk plus are removed during the test. |
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Compression Ratio
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Compression Pressure
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4.6–
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–69
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4.8–
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–73
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5.0–
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–77
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5.2–
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–81
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5.4–
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–85
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5.6–
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–90
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5.8–
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–95
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6.0–
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–100
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6.2–
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–105
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6.4–
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–108
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6.6–
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–113
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6.8–
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–117
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7.0–
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–121
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7.2–
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–126
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7.4–
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–130
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7.6–
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–135
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7.8–
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–140
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8.0–
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–144
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8.2–
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–148
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| A compression test on each cylinder will substantiate the necessity for valve reconditioning. A variation in compression between cylinders of 10 or more pounds is cause for alarm. |
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Compression Ratios
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GRD-214–
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–6.3
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GRD-233–
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–6.3
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