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Bolt Torque
By Wayne Scraba/autoMedia.com
Printable version
Degree of DifficultyEasy
Easy
Estimated Time15 minutes
15 minutes
It’s no secret that nuts, bolts and other fasteners come in all different types, shapes and sizes. The truth is, this isn’t a coincidence. It’s by design. Each fastener is designed to do a specific job in conjunction with a specific material. In essence, every type and grade of metal has a definite limit to which it can be safely stressed or stretched.
Nuts, Bolts and Fasteners Come in Many Shapes and Sizes
One of the most common types of torque wrench you’ll find in motorsports or in professional shops is a “clicker” variety such as this. By definition, a torque wrench is a device that is used to measure or limit the amount of torque that is being applied at a given point (on a specific fastener).
Clicker Torque Wrench
This is a close up of the business end of a torque wrench manufactured by Mac Tools. Adjustment is straightforward: The lock ring is slid toward the handgrip and then the knurled handle is turned to the exact amount shown on the graduations. Setting the tool is like reading a micrometer: It’s simple and extremely accurate.
Business End of a Torque Wrench
Torque wrenches are precision measuring instruments. Treat them accordingly. It’s a wise practice to store the torque wrench in the container it is shipped or sold in. These Mac Tools torque wrenches are sold in protective plastic cases. And that’s where they should take up residence until you need to use them.
Treat Torque Wrenches as Precision Measuring Instruments
Common Mistakes
So what if you don’t tighten a fastener sufficiently. That resolves the over-tightening scenario, but if a nut or bolt is not tightened enough, it will eventually work loose and drop off. On the other hand, getting too rigorous with a bolt in the tightening department will likely snap it off. Neither the “too loose” or the “too tight” situations work. That’s why you should follow specific torque recommendations, and that’s also why you should use an accurate, quality torque wrench.
 
Another big mistake is to test the accuracy of one torque wrench against another wrench. Mac Tools provides this example: “If a Mac wrench is used to tighten a bolt to 90-foot-pounds, and another torque wrench is used to loosen the bolt as an accuracy test for either wrench, then you will likely obtain different readings. This is a test that is frequently performed and it inevitably results in the assumption that one of the two torque wrenches is not calibrated correctly.
 
“What is not generally known or understood is that the break-away or break-loose torque is considerably less than the applied torque. This means that the torque required to loosen a bolt previously tightened to 90-foot-pounds would be considerably less than the 90-foot-pounds of applied torque. In view of the above, it is easy to see why one of the torque wrenches could be considered inaccurate. A torque wrench should be tested on a torque wrench-testing machine to determine its true accuracy.”
 
As you can see, bolt torque isn’t a complex topic, but it’s pretty clear there’s a bit more to torquing fasteners than you might first think. Before you break out the easy-outs and thread repair kit, follow the recommendations made by the Pros. It’s something you won’t regret.
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