| Tight Enough? Working on vehicles as we do, we have to loosen and tighten nuts, screws, bolts and the like as we’re setting up and servicing the vehicles. Some of us have a tendency to “put our all” into it as we tighten up those bolts.There may be something satisfying about pulling a wrench as hard as you can until it won’t move another hair . . . however you aren’t doing the equipment any favors. In fact, most of the torque (bolt tightness) specifications would really surprise you. |
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| Besides the obvious problem of the bolt being impossible to remove by the next guy, there are some more serious issues that arise when a bolt is overtightened. Overtightened bolts undergo more stress than it was designed to handle. This not only applies to the nut, screw or bolt, but also to the framework you’re bolting into. This extra stress can cause the bolt or the nut to fatigue, weakening them and compromising the safety of the machine.Not only that, but many injuries occur during the process of overtightening. You can pull a muscle and the opportunity for the wrench to slip off the nut increases dramatically causing a severe hand injury. | |
| HARDWARE |
Periodically the vehicle should be inspected for loose fasteners. Fasteners should be tightened in accordance with the Torque Specifications table.
Use care when tightening fasteners and refer to the Technician’s Repair and Service Manual for specific torque values.
Generally, two grades of hardware are used in the vehicle. Grade 5 hardware can be identified by the three marks on the hexagonal head. Unmarked hardware is Grade 2.
| TORQUE SPECIFICATIONS | |
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ALL TORQUE FIGURES ARE IN FT. LBS. (Nm) chart specifies ‘lubricated’ torque figures. Fasteners that are plated or lubricated when installed are considered ‘wet’ and require approximately 80% of the torque required for ‘dry’ fasteners. |
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| BOLT SIZE |
1/4″ |
5/16″ |
3/8″ |
7/16″ |
1/2″ |
9/16″ |
5/8″ |
3/4″ |
7/8″ |
1″ |
| Grade 2 |
4 |
8 (11) |
15 (20) |
24 (33) |
35 (47) |
55 (75) |
75 (102) |
130 (176) |
125 (169) |
190 (258) |
| Grade 5 |
6 (8) |
13 (18) |
23 (31) |
35 (47) |
55 (75) |
80 (108) |
110 (149) |
200 (271) |
320 (434) |
480 (651) |
| Grade 8 |
6 (8) |
18 (24) |
35 (47) |
55 (75) |
80 (108) |
110 (149) |
170 (230) |
280 (380) |
460 (624) |
680 (922) |
| BOLT SIZE |
M4 |
M5 |
M6 |
M8 |
M10 |
M12 |
M14 |
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| Class 5.8(Grade 2) |
1 (2) |
2 (3) |
4 (6) |
10 (14) |
20 (27) |
35 (47) |
55 (76.4) |
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| Class 8.8(Grade 5) |
2 (3) |
4 (6) |
7 (10) |
18 (24) |
35 (47) |
61 (83) |
97 (131) |
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| Class 10.9(Grade 8) |
3 (4) |
6 (8) |
10 (14) |
25 (34) |
49 (66) |
86 (117) |
136 (184) |
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Ref Tsp 1
