Torque Wrench Basics and How to Use Them 

Anybody interested in working on their motorcycle will inevitably come up against the topic of torque wrenches. After all, many screw connections on the machine must be tightened using a precisely defined force. Too much force could cause the screw to break off or lead to destruction of the thread. Too little force, e.g. when tightening axle nuts or brake caliper pins, could pose a significant safety risk with potentially dire consequences.

If used correctly, the torque wrench guarantees the precise tightening torque and the optimum clamping force between the screw and thread.

By the way – The tightening torque (M) is calculated from the radius of the lever distance (r) times the applied force (F).

Manufacturers provide specific tightening torques for application-related screw connections in vehicles which can be obtained by referring to the workshop manual or operating instructions for the motorcycle. Examples of these are the axle nuts, oil drain plugs, brake caliper pins, pins on the triple tree, cylinder head screws and various engine screws. If these torque specifications are exceeded, the component could deform and the resulting tension could lead to warping (e.g. of a sealing surface), a thread tearing out or could cause the pin to snap off. 

Furthermore, standard tightening torques exist for standard screws, which depend on the thread diameter, thread pitch, material and quality grade. These can be used for orientation in the absence of any other specifications for a screw connection. These values can be found on the Internet, in the specialist customer- or telephone directory for metal or motor vehicle technology and excerpts of this information are also provided in Screws Basic Info in our DIY tips.

The simplest and normally the most favourable form is essentially a torsion bar, whose rotation in relation to a fixed bar is represented by a value on a scale or dial gauge. When turning the wrench, the pointer must be carefully observed and the turning motion stopped immediately once the reference value has been reached.

With these torque wrenches, the reference value must be set before the application starts. A signal indicates when the reference value is reached. The signals can be heard or felt (click wrenches). However, the signal can also be a slipping (slipper wrench) or folding motion (breaking wrench) or can be shown on a display.

The most commonly used torque wrench is a click wrench and this is therefore described below together with its use.

First, look up the tightening torque for the screw in the workshop manual or operating instructions.  Then fasten the lock at the end of the handle. The value can be set as follows by turning the handle. 

Example 1: A screw is to be tightened to 40 Nm. To do this, turn the turning handle until the reference edge, when turned to the zero position, is exactly aligned with the mark for 40 on the scale.

Example 2: A screw is to be tightened to 44 Nm. To do this, turn the turning handle until the reference edge is in the zero position and lines up exactly with the 40 mark on the scale. Now keep turning the turning handle until position 4 on the turning handle lines up with the vertical line of the scale.

Finally, slide the lock at the end of the handle back into the locking position. The torque wrench is now ready to use.

The screwed connection, previously tightened by hand, can now be tightened with the torque wrench. To do this, fit the torque wrench with suitable attachment (socket wrench nut or bit attachment) onto the bolt and operate the handle of the lever arm, applying a continuous gentle force. 

The set tightening torque being reached is indicated by a noticeable small jerk accompanied by a click noise. Pay attention to the triggering of the wrench! On no account whatsoever should you continue tightening as otherwise you will exceed the set tightening torque. 

If you get the impression during the tightening process that a bolt is unable to withstand the tightening torque or feels "soft" or similar, stop tightening it immediately. The thread is probably defective or the bolt material too soft. Check the components before the thread breaks off and the bolt potentially becomes difficult to remove.

If the component has several parallel screw connections, e.g. cylinder head, tighten the screws in stages: initially with a low torque, then a medium torque and the final torque should be applied in the third step. This allows the workpiece being tightened to settle evenly which prevents it from warping or breaking.

Also bear in mind that some components have several screw connections that must be tightened in a certain sequence, e.g. crosswise or starting from the inside and working towards the outside. In these cases always follow the manufacturer's specifications.

Once you have finished using the torque wrench, it must be unlocked and the adjustment turning handle turned back until the edge lines up with the lowest value on the scale, but not any further. The spring inside the torque wrench is only relaxed in this position. Every continuous load, whether tensile or compressive, would wear out the spring and the accuracy of the display would gradually deteriorate.