How to use a torque wrench?
All to often those that do their own car repair think in terms of force. Whether they are under the hood, or changing a tire, they think the more force they can apply to the different fasteners present on their car, the better.
If you have ever glanced through your car's user guide, however, you may have noticed, particularly when it talks about changing your tires, that the manual recommends only tightening your lugs to a certain amount of lb-ft. That is not referring to how many pounds of extra pressure you should apply to your lug nut wrench as you stomp on the wrench with your foot. Instead, that refers to the maximum tightness the fastener should be tightened to. How is that measured? With a torque wrench, of course.
Even if you have never used a torque wrench, its basic operation should not be totally new to you. Many torque wrenches resemble a simple socket wrench with one major difference. No matter which type, there is some sort of indication of the applied torque to the fastener.
For the uninitiated, the correct amount of torque for any fastener may simply be to turn it until it will not turn any more. On its face, this may seem to make sense. If we do not want something to come loose, we want to tighten it to the point that we also struggle mightily to remove it. After all, that is the only way to make sure it is correctly tightened, right? In practice, however, that can be a very harmful attitude to have.
To full illustrate why a torque wrench should be a part of your tool collection, it is important to go all the way back to the basics and understand what torque is all about. In its purest essence, a fastener is one of the simplest kind of tools. Torque of that fastener is essentially rotational energy about an axis or pivot point, very similar to a simple lever. Properly employed, it keeps your spark plugs in their cylinder head, or your wheels on your car.
Using your car's wheels as an example, think about the effect of torque. Too little torque represents an obvious danger. Over time, the lug will simply come loose and you can risk losing your wheel. Over tightening can be just as dangerous, though. Applying too much torque puts the pivot point under a lot of pressure, and can result in stripped lug nuts, warped brake rotors or even lugs that snap off. Things get even more complicated when you move inside an engine, where there may be gaskets between two parts. Compromising one of those could negatively effect how your engine performs, and lead to long-term problems.
To the rescue are torque wrenches. A majority come in two types, a bending-beam type or a micrometer. Both types have their pros and cons, and which is best for you may depend largely on the job you are using it for.
The bending beam style of torque wrench employs an external pointer that displays the amount of torque being applied to the fasteners as you tighten the fastener. If you are not going to have many uses for a torque wrench, this may be the type for you. The disadvantage of using a bending beam type is that you must be able to look straight at the pointer and gauge as you tighten. If you are under your hood, getting a good view of the pointer may be a challenge. You may also have a hard time fitting the wrench in to tight spaces.
Micrometer wrenches are a more exacting tool, which of course also means it can be more expensive. However, if you are going to be doing more than just rotating tires on your car, this is the wrench to buy. It will be easier to fit into tight spaces, and unlike the bending beam style, a micrometer torque wrench responds by clicking once a fastener has reached proper torque. Some may even release torque once the target it hit. They are a much more fine-tuned tool, and requires special care in handling.
In this way, a torque wrench is unlike any other in your toolbox. While you might not think twice about banging away at a finicky bolt with either a channel locks or your common socket wrench, doing so with a torque wrench is a recipe for disaster. Anything that can throw off the calibration of your wrench is to be avoided. With micrometer wrenches, it is even important to reset the tool back to zero before returning it to storage. A torque wrench should also not be used to fully tighten the fastener, but should only be used at the end when fine-tuning is necessary. While many torque wrenches may also be bi-directional, they should only be used for tightening, and not loosening.
There are some other important tips to make sure your are using your torque wrench as intended. First, every effort should be made to keep the wrench as level as possible when being used. Force should also be applied in the middle of the handle. Having the wrench at a wrong angle, or having your hand in the wrong place when tightening can have a huge impact on the actual torque being delivered to the fastener.
Tightening fasteners to their proper torque helps maximize their abilities, while maintaining the safety and security necessary. It will also prolong the life of all the parts involved.
So do yourself and your car a favor. The next time you tighten sensitive fasteners on your car, grab a torque wrench and keep your feet and your weight off of your lug nut wrench. Your automobile fasteners will thank you.