Doing the Twist: Checking Fastener Tightness

The common ingredients on all race cars include the nuts and bolts used to hold things together. If you look at the simplicity of a nut and bolt, you can see that it is really amazing just how far they have come. They withstand an unbelievable amount of force given their size, but we tend to take the simple nut and bolt for granted.

We've all heard the old saying, "What goes up must come down," and something similar can be said of nuts and bolts: If you tighten, it will loosen. You can be sure that sooner or later your race day will be affected by some nut or bolt loosening up and creating a failure of some type. It may be a simple thing, such as the hardware on a weight bracket, or something as serious as a bolt on a header or valve cover loosening up. These types of failures are completely preventable.

You may be using nuts with a nylon locking ring, and this type of nut can be helpful if you don't use it over and over again. Over time, the locking ability of that nylon ring in the nut degrades and loses its ability to perform as a locking device. If you don't replace this type of nut on a regular interval, then you can't expect it to be much better than a free-running nut, from a locking perspective. That said, it will make disassembly more difficult, as the lock ring will not prevent the nut from loosening, although it will keep it from being a free-running nut. The same can be said of nuts with a metal locking ring.

The other issue with metal lock nuts is that they are very hard on the bolt or stud and can cause more trouble than they prevent. These types of nuts can damage a bolt in the best of environments, and on a race car they can cause problems you do not want to deal with on race days or in the shop (e.g., stripped and/or broken bolts).

There are many chemical locking compounds on the market that you can apply to a bolt or nut to keep it from getting loose when it should be tight. These compounds have their place, and they can work very well. For those products to really work, the bolt and the threaded hole or nut has to be clean and oil free. That's not always a real possibility at the racetrack, no matter how hard you may try to prepare the surface. One other problem is that these compounds often need some time to cure to work properly. At the track, you may find yourself in a hurry with no time to wait for the compound to completely cure. Also, the nuts and bolts could be in an area that gets hot, and the majority of the products available to the racer become liquid and ineffective around 400 degrees F.

Sometimes you just need a mechanical way to keep your nuts and bolts tight and in place. The safety wire (or lock wire) technique is just about the simplest and most economical way to keep nuts and bolts in place. This apparatus is impervious to heat, within reason. If it gets hot enough to melt a stainless steel wire, you have some other problems that will overshadow a loose nut or bolt. The safety wire process is not complex, and if you use the right hardware it is just as effective as any other thread-locking mechanism out there. An added plus is that safety wire is inexpensive and the process can be used over and over again.

Hardware that is already pre-drilled for safety wire application is readily available and not that expensive. The aerospace industry is responsible for the availability of a good number of high-quality fasteners that are already drilled for safety wire.

If you have a special application, there are many tools on the market that will help you drill the hardware yourself. These tools are available for either drilling holes in the threaded portion of the bolt or drilling the head of the bolt on the hex portion or through the corners on the nut. These products are essentially drill jigs and help to hold the bolt or nut in a rigid fashion while you drill. Drilling holes in a standard bolt is not the best solution, as it can severely weaken the bolt. I would suggest obtaining hardware designed with the holes already drilled. They do not cost that much more, and your time may be better spent doing other value-added functions rather than drilling holes in bolts and nuts. However, racers being racers, many of you may opt to do the drilling yourselves.