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Bolt Torque
What is it?
Wayne Scraba / autoMedia.com
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Heat and Tension
Another big factor in the torque picture is heat, primarily in aluminum. Both Mac Tools and ARP note that the thermal expansion rate of aluminum is greater than steel. Because of this, it is possible to stretch a fastener beyond yield as the aluminum expands when heated. The solution? Produce a more flexible bolt.
There’s a definite limit on how much a specific type and grade of metal can be stressed or stretched safely. In essence, that is the elastic limit of the material. Mac Tools states: “After the correct fastener and material have been chosen, the design engineer establishes the exact amount of torque to be applied. This torque specification will induce a stress or elongation of the bolt of approximately 60-70 percent of its ultimate elastic limit.”
Another factor is tension. What is it? According to Mac Tools, tension is straight pull and is measured in pounds. Torque wrenches are at times referred to as “tension wrenches.” This is incorrect. Mac states: “Wrenches that are designed to measure or limit the amount of torque applied to a nut or bolt are definitely torque wrenches.”
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.
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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.
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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).
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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.
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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.
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Re: Chevy 3.8L Engine cutout I would call it in intermediate job. You will need some special tools to do it, but if you have some experience doing repairs, and not jus ... more... |
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