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Stretch is the ONLY way to measure how tight a bolt is. On carillo rods, using 1/4 inch bolts, the 912 engine, the stretch is spec at 0.006 inches. The first time it took 18 foot lbs to get this stretch, the second time it took 16 foot lbs and the third time 14 foot lbs. The threads were being burnished each time, making the torque less. Stretch is the most accurate way as torque will depend on thread condition, lubrication, and whatever. Torque values can vary over 100% for the same tightness, stretch values do not.
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