Cross threaded or torqued, tight is tight. Guten tight. Good enough. I am sure we have all heard these phrases or seen the memes on our favorite social media platform, but what is torque? Is it important? Do all bolts or nuts require a torque? Do you torque on the nut side or bolt side? Are there different types of torque? Hopefully I can answer some of these questions below.
To start off, lets define what torque is in the simplest of forms. Torque is used to create tension in threaded fasteners. It is the application of a force acting at a radial distance and tending to cause rotation. So what does all this mean? It is a way to set a preload tension on the fastener to clamp two joints together. This preload tension will actually stretch the fastener. If you do not torque the fastener enough, the fastener can become loose due to movement of the joints or vibrations. If the torque is too much, the fastener may permanently stretch, no longer applying the correct amount of tension on the joint. If this happens, the fastener is no longer good, and will need to be replaced.
To achieve an accurate torque on a fastener, a torque wrench must be used. This is a tool with a specified range, to precisely apply the correct tightness to a fastener for its specific application. This torque is the result of multiplying the value of force applied by the distance. To help us understand this, we can refer to the picture below. When torqueing a fastener, if the same amount of force is applied at two different distances on the handle of the wrench, the torque will be multiplied. For example 20 newtons of force at 1 meter, will give us 20 newtons of torque. If we move our hand 2 meters down the handle, with the same amount of force, we would achieve 40 newtons of torque (20Nx2M=40N). You can also achieve the same amount of torque by creating a bigger distance or arm, with less force. So, 20 newtons of force at 1 meter, equals 20N of torque. On the flip side, 10 newtons of force at 2 meters, equals the same 20N of torque. This is a very basic principle that should be understood by any beginner mechanic or engineer.
Whew, glad all that math stuff is over, lets get to following a few simple procedures that should be followed to ensure that the correct torque is applied to your fastener.
Make sure your torque wrench is calibrated. This is very important, because if it is not, then you will get false readings, and could possibly under or over torque your fastener. If you ever drop a torque wrench, please get it recalibrated before using again.
Be sure the bolt and nut threads are clean. If dirt or gunk is present on the threads, it can cause more resistance when tightening the fastener, giving you a false torque reading.
Run the nut down as close as you can to the washer or joint surface. If there is friction on the nut while you are running it down the fastener, make sure you measure this resistance and add it to your final torque value. This is called run down torque (torque to overcome the friction of the nut).
Whenever possible, apply the torque to the nut and not the bolt. This will reduce the rotation of the bolt in the hole which could cause wear.
Apply a smooth, even pull with the wrench. If jerking of the wrench occurs, you can get a false torque reading. If this happens, back off the nut and retorque.
Optional - apply torque stripe (LINK TO BLOG POST) on nut of fastener for verification of torqued fastener.
I realize all of this was a little dry, but hopefully was educational, and learning is fun right? So, should you be using a torque wrench for every nut and bolt on your car? Technically yes. Every fastener on your car will have a torque value called out in the maintenance or repair manual. Is this always done? Honestly, no, but understanding the importance of torque, will help you make an educated decision on what you should torque. There are fasteners on the car holding down things like plastic engine beauty covers, that would not be a safety concern if not torqued to the correct specification. Other parts of your car like engine internals, suspension, brakes or drivetrain should always be torqued to the correct specification called out by the manufacturer. Over or under torquing these applications could cause your car to fly apart at speeds, making you lose control and become seriously hurt. If you decide to perform maintenance to your car instead of taking it to a professional, please pick up your cars service manual, and follow the procedures. Educating yourself on these types of things will save you time and money, while making your car safer to operate.
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