Tech Tuesday: Importance of Proper Bolt Torque
NEWS December 13, 2011
Photo by Brian J. Nelson
This week we’re going to cover the importance of using the correct torque values for bolts. Each motorcycle manufacturer has service manuals for the majority of their models which list the suggested torque value for any particular bolt. These numbers are not fictitious numbers that someone with a white coat just decided on, they are important, because each bolt has its own stress point, grade of material and thread tensile strength. The numbers that are given in manuals are the values that not only result in the proper tightness of the bolt, but also allow for flexibility and expansion, if needed.
One example that we will use to diagram the importance of proper torque values is a swing arm pivot bolt. There are usually three or more sets of torque values that are associated with this item alone. For the demonstration today, we will be using the 2007 Suzuki GSX-R750 and will be referencing Suzuki’s service manual for that model to identify the proper torque values and procedures.
The first step is to ensure that you have the proper protective equipment and tools needed to complete the maintenance task safely. In the very front of the Suzuki service manual, there is a chapter called precautions. This is a great source of information which describes the protective equipment and procedures needed to complete any tasks that will be performed based on the manual. The second chapter is about the proper tools that are needed to complete any service task on the motorcycle. You will also see in the manual that you should inspect all of your equipment for proper functionality before beginning any maintenance task.
On to the task at hand, the manual explains that the main pivot bolt threads through the frame into the swing arm. This bolt needs to be torqued to ensure proper placement of the swing arm, specifically the spacing between the swing arm and the frame. The pivot bolt pushes on the spacers/inserts in the swing arm, which rests on the bearings. If the pivot bolt is over tightened, it can wear on the bearing and cause major drag or bearing failure. If the pivot bolt is too loose, it will not allow the spacer/inserts to seat correctly and the swing arm will have free play in the frame. This can cause bearing failure, binding in the swing arm movement and other catastrophic failures.
Next, the locking nut usually has a washer and some form of locking mechanism on the threading of the nut itself. The locking nut has to be torqued properly to ensure the proper swing arm pinch. When this locking nut is too tight, it may cause binding in the swing arm movement, in turn hindering the suspension activities. When this bolt is too loose, binding in the swing arm movement may also occur, as well as potentially losing the nut or even the swing arm pivot bolt entirely.
Lastly, there is a swing arm pivot locking nut, also known as a castle nut. This swing arm pivot locking nut holds the pivot bolt in place without letting it back up out of its originally torqued place and ensures proper alignment in the frame. The swing arm pivot locking nut is usually a softer compound than the swing arm pivot bolt and can gouge much faster. On the 2007 Suzuki GSX-R750, this nut also requires a special tool for correct installation.
The swing arm pivot bolt is just one example of an item on your motorcycle that needs proper fastener torque procedures. Each fastener on your motorcycle has its own procedure and value but the importance of each is just as critical as the swing arm example cited above. This example was for a Suzuki GSX-R750, but each manufacturer makes service manuals for the majority of their brands available to the general public.
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