Lately I feel like all I’ve been doing is telling people they need to safety wire their cars. Specifically exhaust hardware on turbo vehicles. I’m surprised how many people have never heard of the technique or understand its purpose. If you have any doubts of the need for safety wire, you need only to look at the rulebook of any regional motorcycle race event – where it is MANDATORY to safety wire a number of components, including the oil drain plug, fill cap and filter.
So to begin: Safety Wire(ing) is the process of using thin stainless steel wire to hold a bolt head or nut in place, and to make it impossible for that fastener to loosen. You can safety wire hardware to other solid parts, or to other nuts and bolts in a pattern that they will all keep each other tight.
What’s the point?
The reason its so important to safety wire exhaust components (specifically on a turbocharged car) is because when the system gets red hot everything expands so much that it can stretch or yield the bolts holding the assembly together. As it cools, it seems the bolts lose their clamping force and can loosen – eventually to vibrate right off of the assembly. It’s not that you didn’t tighten them – it’s that the cycles of extreme heat and cooling cause the hardware to loosen off. Safety wiring these bolts ensures they can never vibrate loose – even if they lose all of their clamping load. This is why different types of locking nuts and other locking fasteners do not work in this application:
Nylon nuts melt the nylon. Lock washers get so hot they lose their spring. Serrated nuts don’t work if the bolt or stud stretches. Metal distortion nuts do work, but they destroy the stud upon removal and so are not a good option for cars where we dis-assemble these things every year. Welding sometimes does not even work, as the heat and expansion cracks the tack welds.
How To Safety Wire:
Start with some thin safety wire that you can purchase from a number of places, including Brafasco, Aircraft Spruce, and other hardware supply places. You’ll also need a set of safety wire pliers if you want to do a nice job. Before you’re able to safety wire, you’ll need to drill the bolt head or nut to accept the safety wire. If you want to be proper, you should always tighten the bolts in place first, mark where you want to drill the hardware. This ensures you can line the bolt heads up perfectly so that the wire is laid out in the best possible arrangement. However, this is unrealistic for most of us. No matter where the bolt holes end up, you can always run the wire in the correct orientation so that it is “pulling” the bolt head tight – so don’t worry too much. There are a number of nice drilling jigs available that make drilling bolt heads and nuts easier, but you can always just use a vice.
Safety wire pliers spin the wire into a nice tight braid by pulling on the bottom of the handle.
Buy the safety wire that comes in a tube, it’s easier to work with. 0.032″ is a good size.
When drilling nuts, you need to drill through the corner of the hex so that you do not pass through the threads. This way you don’t have to first tighten the nut, and drill through the nut and stud with the part assembled (which is sometimes impossible). The nut drilling jigs from Pegasus and other vendors make this a lot easier, but you can also do it in a vice if you are careful. Once you’ve drilled the bolts for safety wire, tighten all of the hardware in place – its now time to safety wire.
Pegasus has a nice safety wire jig for drilling nuts – which goes through the corner of the hex so you do not need to pass through the threads.
A typical bolt head safety wire jig as offered by Aircraft Spruce
The key is to route the wire in a way so that if bolt were to try and loosen – it would be constrained by the wire. You can imagine that only one side of the bolt head will “pull” when loosening, and one side will loosen. Having the safety wire on the wrong side would allow the bolt to back off 180 degrees before the saftey wire stops it from turning further. You want to spin the wire with your tool between all of the mounting points or bolts, so that the wire is protected. Be very careful not to nick or damage the wire – broken safety wire is not going to help you. Here are a few examples:
These example layouts show different arangements to tie 3 bolt heads together. Notice that if you were to try and loosen any of the bolt heads they would be held by the wire – and the wire would be pulling the opposing bolt head tighter as well.
How to tie two bolts together, and one bolt to a fixed plate or bracket.
If a picture is worth 1000 words, then a video is worth 1,000,000 words. Watch these youtube videos to get a better idea on how to safety wire.
Here’s some random guy with no sound safety wiring what looks to be a Volvo fuel rail: http://www.youtube.com/watch?v=HfasycekSLo
Some crazy jet engine that is fully safety wired (he calls it lock wire): http://www.youtube.com/watch?v=OwFjUX6SaY8
Finally, some bro named Jimmy teaches you how to safety wire a bike: http://www.youtube.com/watch?v=oOEbMsi-2QU
That’s it guys. Hopefully this helps – please safety wire all turbo and wastegate components of any turbocharged car, and use stainless hardware. It can’t hurt to safety wire other items like drain plugs, bolts, and specifically any other fasteners that are hard to check or inspect – it adds a bit of peace of mind.