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Old 11-18-2005, 06:07 PM   #1
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Tightening Torque

I just bought a Workshop CD and start reading it. It mentions about tightening torque for almost all screw-tightening move. For example, tightening tongue should be 3-4Nm for the MAF screws.... 50Nm (37 ftlb.) for the oil plug...etc. Do I need to care about tightening torque if I am not using powered tools? How do I know how much tongue I put when I use a manual screwdriver or nut driver? How critical is tightening tonque??

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Old 11-18-2005, 07:15 PM   #2
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For bolts it's very important. Torque values are set to make sure a bolt is tight enough not to come out, but not so tight it damages the threads or completely strips them. The smaller bolts that are holding two parts together with a gasket sandwiched between them are torqued to make sure the gasket seals properly. Over-torqued can cut or damage the gasket and under-torqued can leave gaps and cause leaks. Bolts that are on spinning or vibrating parts will often have two torques. The first allows the bolts to be evenly tightened around the part, then the second makes sure they tightened to a point where they won't back out.

For small screws, it's about impossible to torque them with regular tools. The torques are mostly set to make sure you don't break plastic parts that are being held with the screw. You just need to make sure you're not allowing the screw to dig into the plastic or metal that it's holding down.
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Old 11-18-2005, 10:26 PM   #3
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Actually, to understand Torque, you need to understand how Threaded Fasteners work.

Nuts, Bolts and Machine Screws work because they are elastic. Tightening them to spec actually stretches them and imparts an Elastic Tension between them, It is this Elastic Tension which keeps them from coming loose. Without it, they would soon loosen due to vibration, changes in temperature (expanding and contracting), etc.

Too much Tension and you will exceed the strength of the Threads, causing them to give way - Strip. Too little tension and the Fastener doesn't stretch sufficiently to hold and will eventually work itself loose. Ever notice that once you bolt something down completely you can still turn it a good to a Full Turn? This is the Fastener stretching.

Using a measuring device such as a Torque Wrench, or a Torque Angle Meter, allows you to control the specific amount of stretch which you impart to the Fastener which is often expressed as Nm or Ft./Lbs.

One more thing about Torque Specs, unless specifically stated, all Torque Specs assume a Dry Thread. Fully 50% of the Torque you apply is necessary to overcome the Friction of the Threads, and this is factored into determining the Torque Spec. Using any kind of Lubricant, ThreadLocker, whether liquid or dry, eliminates this Friction between the Threads. If using any Lubricant or ThreadLocker on a Fastener (unless specifically noted in the Torque Spec), you need to reduce the Torque Spec by 50% (a good Rule of Thumb) to prevent overtightening the Fastener.

Torque Specs on a Wood Screw or Sheet Metal Screw are less important as these primarily use the Friction between the Threads to hold. Hope this helps...

Happy Motoring!... Jim'99
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Old 11-19-2005, 09:07 AM   #4
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Thank you all once again! I think I will go buy a Torque Wrench or Torque Angle Meter.

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