How to Select and Use a Torque Wrench
How to select and use a torque wrench is a skill you will require if you intend to work on your vehicle, motorcycle, or boat. There are many pieces on these vehicles that will require setting torque values during reassembly. This article will present the various types of torque wrench styles and how to use each one. The choice of a torque wrench should be based on the vehicles or equipment it will be used on and the torque value ranges that are required.
Type of torque wrenches
How you use a torque wrench depends on the type of torque wrench it is. There are several styles of torque wrenches. Torque wrenches come in different physical sizes. They also measure different torque values. Also, they can be 1/4″, 3/8″, or 1/2″ drive or larger. So let’s look at the first thing, torque wrench styles.
Style of torque wrench
There are many styles of torque wrenches. But let’s look at the four styles of torque wrenches used on autos, boats, and motorcycles.
Beam style
The beam style wrench is the simplest type to use. It does not have a setting for torque target value it just flexes when tightening which moves a scale across a pointer. There is no indication(audible or mechanical) left behind by the torquing action. You must watch the needle as you apply torque to the bolt.
Dial style
The dial style torque wrench is a little more complex than the beam style. The torque target value can not be set. It has a dial that is set to zero. It has two needles that sweep across the dial when applying torque. Both the needles move, but only one moves when the torque wrench tightens. The other needle is pushed by the moving needle and leaves an indicator of how much torque was applied. You must still watch the needle while you tighten the bolt. The indicator needle will need to be returned manually to zero after each torque application.
Dial Torque Wrench with Red Blue Needles
Click Style
Click style torque wrenches are the most common style you can find. The torque value can not be set until a lock mechanism(differs by manufacturer) is released. The proper torque value is set by using a labeled/etched scale on the tool(large increments) and the handle(fine adjustments). Rotate the knurled handle of the tool to set the final torque value. Then lock down the mechanism.
As you tighten the bolt the torque wrench will “click” when it reaches the torque value you have set. This style of torque wrench does not require that you view a dial or needle you simply listen for the “click” to verify that you have achieved your set torque value. It is immediately ready for the next torque application. It does not need to be reset.
How to set a torque value target on a click torque wrench
Example of how to set the torque wrench below to a target torque value of 29.5 inch-pounds.
- Loosen the lock mechanism.
- The increments on the torque wrench body are marked in 5 inch-pounds.
- One complete rotation of the knurled handle equals a change of 5 inch-pounds.
- Rotate the knurled handle so the zero on the handle lines up with the horizontal 25 inch-pound line at the vertical line.
- The divisions on the knurled handle are marked in .5 inch-pounds
- Continue to rotate the knurled handle past the 25 inch-pound mark until the number 4.5 on the handle lines up with the vertical line.
- Tighten the lock mechanism.
- Congratulations you’ve set the torque wrench target to 29.5 inch-pounds.
Scale for setting torque value in inch pounds
Electronic/Digital Style
This is the most complex torque wrench you can buy. First thing, it will require batteries. It can be set to any value you desire within its range by pressing buttons. This torque wrench has an LED display of the set torque value. It can have a vibration or an audible beep when you have reached the torque target. Also, this style of torque wrench can be used for angle values if so equipped. It can come in the normal shape(with a handle) or it can be shaped as an adapter that will fit onto a standard ratchet or breaker bar.
Digital Torque Wrench LED Display in Newton Metres
Torque wrench range
Ok, let’s look at the second important thing physical size and torque range. But that’s two things, right? Let’s look at the range. Torque is measured in different values. Those measurements are Newton metres, foot-pounds, and inch-pounds. There are other measurement values that are used but let’s concentrate on only those values used on autos, motorcycles, and boats.
Not all torque wrenches are built the same. Two torque wrenches with the same physical lengths and drives(1/4″, 3/8″, 1/2″) can have different torque ranges. One torque wrench can have a range of (10-150 ft lbs) while the other wrench has a torque range of (50-150 ft/lbs).
As a general rule of thumb, the physical size of the torque wrench will be different for ones measuring in inch-pounds(3/8″ drive or smaller) versus those that measure in foot-pounds(1/2″ drive or larger). So a torque wrench that is used for inch-pounds can be rather small. While a wrench that is measuring in foot-pounds can be physically two to four feet in length.
But don’t count on this rule as being absolute. I have seen 1/4″ drive torque wrenches that measured in foot-pounds. Always check the range of the torque wrench you are interested in purchasing. Personally I like the 1/2″ drive size for high-value torque targets. I wouldn’t want to be applying 80 ft-lbs of torque on a 1/4″ drive torque wrench, it would feel like I was going to twist off the drive or tear the socket apart.
Storage
For click (or other micrometer) types, when not in use, the force acting on the spring should be removed by setting the scale to its minimum rated value in order to prevent permanent set in the spring.
No-Noes
- Never use a torque wrench for loosening bolts. It is not a breaker bar, it could impact the calibration of the wrench.
- Never drop a torque wrench.
- Don’t put the click torque wrench into storage with it set to a torque value, zero it.
Torque wrench configurations
Torque wrenches can come in different configurations. Just like ratchets, they can have flexible heads that will allow an angular change. I prefer a fixed head ratcheting torque wrench especially in models that measure in foot-pounds. The reason being that I don’t want the torque wrench to be able to move sideways when setting a high torque value, for example, tightening lug nuts on a wheel. If I need head flexibility I’ll add an adapter such as a wobble extension or a universal joint.
Newton metres, inch-pounds, foot-pounds
Torque wrenches measure different torque values. If you are shopping for a torque wrench check that the wrench is measuring in the correct value and with a large torque range. Some models of torque wrench have scales for both Newton metres and foot-pounds so you don’t have to purchase two tools.
There are websites that will convert Newton metres to foot pounds if you don’t wish to purchase a separate Newton metre torque wrench. Inch-pounds can be easily converted to foot-pounds by dividing by twelve. You can use the following website for converting inch-pounds to Newton metres.
How to use a torque wrench
When you use the torque wrench you will need to approach the target torque value as a precision operation. The style of torque wrench does impact how you use it. You may need to view a dial or needle, or look at a scale or listen for a click or audible signal.
Whatever torque wrench you have chosen when using the torque wrench, as you get close to the torque target you will need to apply slow, steady pressure until you hear or see your target achieved. It is very easy to over tighten the bolt if you jerk the torque wrench while tightening.
If you’re using a click-type torque wrench return it to its lowest torque setting before storage. If the torque wrench comes with a case keep it in the case to protect it from accidental banging. No case? Store the tool separate from other tools. Want a DIY calibration check of your torque wrench? Check out this procedure with pictures.
That’s it you now have all the information you need for how to select and use a torque wrench.
My torque wrenches
I have two torque wrenches. One torque wrench for foot-pounds. It is a 1/2″ drive, ratcheting, fixed head click type wrench. Its range can easily handle the high target torque needed for autos, motorcycles, and such. I also have a 3/8″ drive, ratcheting, fixed head click-type torque wrench for inch-pound torque values. If I need to use Newton metres I convert them to foot or inch-pounds. Between these two wrenches, I haven’t found a target torque that I couldn’t achieve.
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