Is there any tightening torque loading general guideline for automobile?

Answer 1

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Always use the proper grade fastener. You should use at least grade 5 fasteners on almost everything on your motorcycle. Bolts are graded by tensile strength and are easily identified by the number of slash marks on the head of the bolt. The more marks the higher the quality. Hardware store bolts with no markings on top are usually soft, mild steel, grade 2 quality and should be avoided like the plague.

Another thing to watch is torque specs. A bolt that has been over tightened can be just as lethal as one that hasn't been tightened enough. A bolt that has been tightened beyond recommended torque specs can easily break in service. In other words the soft grade 2, 5/16-18 hardware store bolts that are attaching the bottom of your sissy bar to the back legs of your rigid frame are shaky enough to begin with, they get downright lethal when you tighten them up as tight as you can get them with a couple of 10" wrenches. Keep in mind that torque specs will be less for bolts that have oil or lubricate on them than for clean, dry bolts. Use the following tables to determine what grade of bolt you are working with and how tight to torque it.

U.S. BOLT GRADES

SAE 2 SAE 5 SAE 7 SAE 8

2 5 7 8 SOCKET HEAD CAP SCREW
I.D. Marks No markings 3 lines 5 lines 6 lines Allen head
Material Low carbon Medium-carbon, tempered Medium-carbon,
quenched & tempered Medium-carbon, quenched & tempered High-carbon, quenched & tempered
Tensile strength (Minimum) 74,000 psi 120,000 psi 133,000 psi 150,000 psi 160,000 psi

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U.S. BOLT TORQUE SPECIFICATIONS
Torque in pounds-foot
2 2 5 5 7 7 8 8 Socket head cap screw Socket head cap screw
Bolt Dia. Thread per inch Dry Oiled Dry Oiled Dry Oiled Dry Oiled Dry Oiled
1/4 20 4 3 8 6 10 8 12 9 14 11
1/4 28 6 4 10 7 12 9 14 10 16 13
5/16 18 9 7 17 13 21 16 25 18 29 23
5/16 24 12 9 19 14 24 18 29 20 33 26
3/8 16 16 12 30 23 40 30 45 35 49 39
3/8 24 22 16 35 25 45 35 50 40 54 44
7/16 14 24 17 50 35 60 45 70 55 76 61
7/16 20 34 26 55 40 70 50 80 60 85 68
1/2 13 38 31 75 55 95 70 110 80 113 90
1/2 20 52 42 90 65 100 80 120 90 126 100
9/16 12 52 42 110 80 135 100 150 110 163 130
9/16 18 71 57 120 90 150 110 170 130 181 144
5/8 11 98 78 150 110 140 140 220 170 230 184
5/8 18 115 93 180 130 210 160 240 180 255 204
3/4 10 157 121 260 200 320 240 380 280 400 320
3/4 16 180 133 300 220 360 280 420 320 440 350
7/8 9 210 160 430 320 520 400 600 460 640 510
7/8 14 230 177 470 360 580 440 660 500 700 560
1 8 320 240 640 480 800 600 900 680 980 780
1 12 350 265 710 530 860 666 990 740 1060 845

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BOLT TORQUE FACTORS