I have been getting my hands dirty since early 2000. That falls a little more than a year before the first revolutionary Pulsar was launched. As time passed by, I delved deeper into the nitty-gritty of motorcycles. I transitioned from tightening the brakes to mild maintenance of the whole motorcycle. After practicing on a few 110cc motorcycles, I tired on a few Pulsars and Karizmas. I still remember the first time I tried tightening the tappets of a Pulsar, only to end up overdoing it. Little did I know about things like rotating force and the axis which needed to be applied to tighten a bolt, whether it was a drain plug or an axle nut, let alone a tappet.
So here I am, after working on tuning, and using more than a dozen motorcycles over these years, to tell you about torque and its importance.
Let’s understand torque first. Torque is a combination of forces applied from a distance from an axis to create a twisting action. Now I am pretty sure everyone reading this must’ve operated a door latch that has a lever which rotates 90 degrees to open and close. So, the place where the key inserts is the axis. Now, imagine if the actual handle is too short to operate, you would need more force to pull the lever down, wouldn’t you? Contrarily, if I double the length of the handle, I will get the same torque at axis but with half the force. Hence, torque is all about the lever arm length, the door handle in this case.
Now let’s look at the relationship between the lever arm length and the force applied at the end of it. Torque isn’t just limited to nuts, bolts or other fasteners on a motorcycle. Its also a significant factor in acceleration. Bolts, are used to clamp parts together. The bolt’s fitting location decides the size and type of a bolt, depending on the stress it will undergo. A lot of calculation and testing has been done to determine the right size and type. But it is not only limited to what size and type of a bolt is used, but the how much to tighten it. This is crucial. When two parts are clamped together using a nut and bolt, there is continuous friction between them.
Importance of bolt tightening
There is also a fair chance that a bolt might break if it is tightened too much. That’s because of its insertion into the threading hole. Also due to tightening it with the nut from the opposite side as the bolt starts to stretch to occupy the hole fully. Simultaneously there is an equal and opposite force applied on the same. When the clamped parts are operated, basically acting like a spring, until a point. If the bolt is tightened too much, it stretches to a point that it exceeds its ‘elastic limit’. This leads to deformation and breakage.
On the other hand, if the bolt is too loose, it will not hold the clamped parts together, which will makes life miserable (as you can imagine). This is why there is a torque range usually mentioned in a service manual for specific parts on a specific motorcycle, a recommendation given by the engineers who made the motorcycles.
Correct application of the torque
Now that we know what torque is and why there are different sizes and types in it, how do we ensure that we are applying the right torque on right bolt? Well, the answer to that is a simple tool called a torque range spanner or, simply, torque wrench. This tool allows you to tighten every single bolt within its recommended torque range. Of course there are lot of them out there, but you can start with the basic ‘click-type’ torque wrench that you’ll find in most automotive retailers or online as well. However, torque wrenches usually come only with the lever arm, not the sockets that are used for different bolts. So you might want to buy them separately.
The basic ones in the market start with 1/8 inch drive torque wrench. This should be good enough for you to start some basic motorcycle work. It comes with a decent range of torque values. After adjusting the scale for the torque at the socket end, it will make a ‘click’ sound. This is to tell you that you have reached the bolt’s desired torque.
- There may be times when the service manuals might not have the same units which the torque wrench has, however, there are many apps that convert the value in a jiffy.
- Always check whether the service manual says that the bolt is supposed to be dry or lubricated while tightening it into a thread hole.
- Always keep the movement as smooth as possible while tightening or loosening the bolt.
- Storing the wrench is as important as using it for the right torque. Even the basic ‘click type’ torque wrench is considered to be a precision instrument. It has a spring loaded in the handle. This spring stretches and retracts every time you change the setting. So it is a good practice to loosen the tension off the spring.
- There are ways to calibrate a torque wrench in your own garage if you do not have access to bigger garages where calibration is a regular once-a-week practice.
- Most torque wrenches are supplied in a plastic case nowadays. Do store them in the case; or worst case just keep them somewhere where they’ll avoid knocks.
- Finally and most importantly, do not drop them!
Words by Vishal Joshi