Know your torque wrench

We should all have a torque wrench and know how to use it. Alisdair Cusick walks us through the rights and wrongs of using one

We should all have one, but what’s the rights and wrongs of using one?

ALL Land Rovers use fixings to hold parts together, and those fixings, wherever they are, work by being under tension, which causes the fixing’s threads to grip and hold. Too much tension will strip threads, crack heads off bolts, or damage alloy casings. Too little will mean the items don’t work as intended, wear rates increase, or worse, fixings work loose. Rather than use the Mk1 elbow and guesswork, there’s a tool we should all own for those times when we need to be certain of a fixing’s torque. Indeed, the torque wrench is an essential for fixings requiring to be tightened to a certain torque as specified by Land Rover.

Torque is a turning effect (or turning moment). It’s simply the amount of force applied multiplied by the leverage (distance from the bolt centre to where your hand is pulling on the spanner). Thus, torque is shown in units of force and distance, such as 50 pounds force feet (lbf ft) in imperial units, which is roughly 68 Newton metres (Nm) in metric units. To illustrate this, if you put a 1 foot long spanner on a bolt head and pulled from the end of the spanner with a force of 50 lbs, the torque you initially applied to the bolt would be 50 x 1 = 50 lbf ft. If using a 2 feet long breaker bar with the same pulling force, you would apply a torque of 50 x 2 = 100lbf ft.

It’s important to be aware of this when using the device. Torque values are usually given for dry fixings, new, and free from corrosion because friction dictates the torque value. Heavily corroded or damaged fixings may not be fully tightened even though the torque wrench registers the intended value, because part of that torque is overcoming the restriction on the threads, rather than tightening the bolt in the way intended. Likewise, fixings slathered in oil will over tighten due to lower friction. Every fixing will have a torque value which you’ll find in the workshop manual. Note that some bolts, such as cylinder head bolts are single use because they’re designed to stretch. They also might have a torque value plus setting, meaning a value plus a specified number of degrees further tightening.

Torque wrenches come in four principal types: beam, where a pointer refers to a scale on the wrench arm; dial, where a dial shows the measurement of the applied torque; click, where the arm clicks as the specific torque is reached; and electronic, where an audible beep or buzzer is heard at the specified torque. Some are simpler to use than others. You may struggle to read a beam wrench under a dark bonnet when doing head bolts, and an electronic version always needs a good battery – though its ability to store a number of values for instant recall is useful.

Because torque values vary from small to large, they are available with various size drives. If you want one for common uses, then a good half inch drive click torque wrench will be the one you reach for the most.

To make them last as long as possible, the sacred rules are never to use them as a breaker bar, nor to undo fixings. Store them carefully, keep them clean, and always return them to zero after use. It is possible to have them recalibrated, and that’s worth doing. Contact your tool’s manufacturer for their service department.