How to Use a Torque Wrench

using a torque wrench on a jet engine
Whether it's a lawn mower blade, wheel nut, or intake bolt, using a torque wrench will assure proper assembly. https://media.defense.gov/2015/Dec/11/2001497257/-1/-1/0/151210-F-IE661-025.jpg

Wheel nuts, like ketchup bottles, always seem to either be too tight or too lose. When it comes to wheel nuts, too loose and you might make a mess or lose a wheel. Too tight, and you might need pliers come grilling time or you could break something. Unfortunately, it seems most DIYers tend to err on the side of “tighter is better,” leading to frustration, broken bolts and threads, even damage.

For convenience, repeatability, consistency, and safety, engineers specify how much fastener compression is needed for every cap – yes, there is a ketchup bottle cap torque specification – screw, bolt, nut, sensor, and spark plug. Every DIYer needs to learn how to use a torque wrench at have at least one or two in the toolbox.

What Is a Torque Wrench?

a beam-type torque wrench
Invented about 100 years ago, the beam-type torque wrench measures twisting force. https://commons.wikimedia.org/wiki/File:Western_Forge_Craftsman_beam_torque_wrench.jpg

When it comes to both opening ketchup bottles and tightening wheel nuts, torque is an important measure to understand. Torque an indirect measurement of how much compression the bottle cap or wheel nut is exerting on the bottle or the hub, wheel, and brake rotor. We say “indirect” because there’s no practical way to measure compression or how much the bolt stretches, but what is “torque,” anyway?

Torque is a measure of twisting force, typically expressed in lb·ft, lb·in, or N·m (pound·foot, pound·inch, newton·meter), that is force times distance. To visualize this, imagine removing wheel nuts with a 2-ft breaker bar. With the socket fixed on the wheel nut, applying 50 lb of force to the end of the breaker bar results in 100 lb·ft of torque on the wheel nut, that is, 50 pounds force multiplied by 2 feet of lever. With a 3-ft breaker bar, you’d only need to put 33.3 lb of force to get 100 lb·ft of torque, while a 1-ft ratchet would require 100 lb of force.

Since human beings weren’t made with calibrated force meters in their hands, there’s no way to consistently measure how much force you put on a wrench and how much torque you put into a nut or bolt. A calibrated torque wrench is exactly what you need to ensure proper tightening of everything from oxygen sensors and spark plugs to valve cover gasket bolts, wheel nuts, and cylinder head bolts.

Types of Torque Wrenches

diagram showing the function of a click-type torque wrench
Internally, a spring and detent device enables a click-type torque wrench to detect when a certain amount of force is being applied. https://commons.wikimedia.org/wiki/File:Direct_pawl_clicker_torque_concept.png

Depending on the application, there are several torque wrench types available, but three of them are most-common in the automotive field, including beam, click, and electronic torque wrenches. Each type works slightly differently to accurately measure how much twisting force you apply to a given fastener.

  • Beam: Invented about a century ago, beam-type torque wrenches are the simplest and easiest to use. The main beam has a handle on it, which you use to apply force to the socket. The indicator beam is fixed to the socket head and does not move when tightening a fastener. The gauge on the main beam measures the distance that it’s deflected, giving you a torque reading.
  • Click: Click-type torque wrenches look more like standard ratchets, though they have special internal mechanisms for measuring torque. The most common is the micrometer-adjust, which compresses a spring inside. The spring presses a ball or cube, which sits in a detent in the head. When the specified torque is reached, the ball or cube shifts out of the detent, making a click sound. The tighter the spring, the harder it is to push the ball out of the detent.
  • Electronic: Using a piezo-electric sensor, which changes resistance depending on how much it deforms, electronic torque wrenches have no moving parts. Electronically, they sense how much twisting force is applied to the socket, delivering a readout on a digital display. For setting a specified torque, the display can usually be set to blink, vibrate, or beep when reached. Electronic types may also include a torque-angle function.

Beam torque wrenches don’t ratchet, and can be used for tightening or loosening. Most click-type torque wrenches are ratcheting, and may be used for tightening or loosening, though some only allow you to apply tightening torque. Beam and click-type torque wrenches can be used for loosening, but exceeding the maximum torque specification can damage the wrench. Split-beam torque wrenches should only be used for tightening, as loosening can cause damage to the wrench.

Torque Wrench Sizing

a typical nut and bolt
The size of the fastener and its application dictate how much torque it requires and which torque wrench you'll use to tighten it. https://commons.wikimedia.org/wiki/File:EN_14399_Pre-load_bolt_assembly_(System_HR).png

To use a torque wrench properly, the first thing you need is a torque specification. Torque specifications are found in the repair manual, but not usually in the owner’s manual. The torque wrench you choose will depend on the torque specification – you wouldn’t use a small pound·inch torque wrench on a wheel nut, and you wouldn’t use a large pound·foot torque wrench on valve cover bolts.

  • Small torque wrenches, ranging from 10 to 250 in·ft, are useful for valve covers, throttle bodies, transmission valve bodies, some intake manifolds, and interior fasteners.
  • Medium torque wrenches, ranging from 5 to 100 lb·ft, are useful for engine accessories, suspension components, brake components, interior components, and some wheel nuts.
  • Large torque wrenches, ranging from 20 to 250 lb·ft, are useful for cylinder head bolts, major components, wheel nuts, and wheel bearing hubs.

Use a Torque Wrench Properly

assembling an automatic transmission valve body
Proper torque is essential for proper sealing and longevity. http://www.gettyimages.com/license/171384362

Any torque wrench requires a firm and steady hand. If there is a torque sequence, such as for tightening wheel nuts, cylinder head bolts, and some internal engine and transmission parts, follow the steps carefully to prevent damage and ensure proper operation. Some fasteners, such as torque-to-yield cylinder head bolts, require an additional measurement, beyond twisting force. After setting the bolt to a specified torque, an additional angle will be specified, turning the bolt further, regardless of torque. You can sometimes use paint marks, but torque-angle gauges and electronic gauges are more accurate.

To use a beam torque wrench, watch the gauge carefully until it reaches the torque required, then stop applying force to the handle. To use a click-type torque wrench, whether it’s a spring or split-beam, adjust the dial and lock it in to the required torque specification, then gradually tighten the fastener. When the torque limit is reached, you’ll feel and hear a “click” in the handle, at which point you stop applying force. Electronic torque wrenches are used in similar fashion as click-types, except the adjustment and notification is electronic. When torque is reached, signified by a beep, vibration, or flashing light, stop applying force to avoid over-tightening the fastener.

Split-beam and beam torque wrenches don’t need any special care on storage, but micrometer-adjust click-type torque wrenches should be zeroed out. This will prevent the spring from “setting” and skewing future torque readings. Torque wrenches should be stored in their protective cases and never dropped. About once a year, you should have your torque wrench calibrated to keep it within tolerances.

The Ketchup Bottle

By the way, a plastic ketchup bottle with a 28-mm plastic cap seals best at around 14 lb·in torque – tighter is not necessarily better.