What about washers? The purpose of a washer is to distribute the load under the bolt head and nut face. However most washers can move during the tightening process causing problems. This sort of defeats the whole purpose.
One alternative it to use something called an SAE Flat Washer. These are a tighter fit on the bolt and they have a smaller outside diameter. They’re usually made from a low carbon steel and zinc coated.
If you’re serious about washers you should look at the ARP or Pegasus catalog. They have a huge selection of washers. They have washers that are made from chrome moly steel and are parallel ground. If you need a washer for a 3/8” diameter bolt ARP makes it in four different outside diameters and three different thicknesses.
You can also go to an aircraft supply company where the array of washers is even greater. Most aircraft washers are manufactured with a +/- of .005” outside and inside diameter tolerance. You can even get stainless steel washers.
Instead of using flat washers some people prefer to use flanged fasteners. A flanged nut is simply a nut with an integrated washer. One problem that can occur with washers is that they can move when being tightened so that the washer can rotate with the nut or bolt head rather than remaining fixed. This can affect the torque tension relationship. You end up measuring the friction between the washer and the head of the bolt. A flanged washer eliminates that possibility.
Locking the nut in place: Let’s assume you’ve done everything correctly and the tension on the bolt is correct. Nuts can come loose simply from vibration or changes in temperature. This allows movement that results in a loss of tension. The most common solution is to use a chemical thread locker, which is an adhesive that uses anaerobic technology. The chemicals fill up the thread engagement area. You can use a thread locker on any nut, bolt or threaded component.
These threadlockers come in different strengths. Loctite has three classes: Low, medium and high strength. The low strength allows disassembly using hand tools. If you use the medium strength disassembly is still possible with hand tools. Once you get to the high strength such as Loctite 272 or 278 you might need to apply heat to loosen the nut. If you’re going to use these chemical as locking devices make sure you go to their web sites and learn about them.
How many threads should be showing? If the end of the bolt is flush with the face of the nut you’re not getting full engagement with the threads. Look carefully at the end of any bolt and you’ll notice a partial starting thread. In order for there to be full engagement a full thread must exist This means that you want one to two full threads protruding past the face of the nut.
If you’re going to avoid thread stripping the full height of the nut should be used. Make sure that the thread protrudes through the nut. Also use a standard height nut as this is designed so that the bolt will break before the threads start to strip. Jam nuts are simply not suitable.Studs vs. bolts: This is really a question about your engine hardware. It’s also an easy one to answer. Whenever possible it’s better to use a stud rather than a bolt. When you use a stud there is a more accurate and consistent torque loading. Consider that when you’re installing a bolt you’re actually twisting the bolt as you reach the final torque setting.
Studs on the other hand are installed in a relaxed mode. At least they should be. Never use jam nuts to install a stud. Now when you place the cylinder head on the block and tighten the nut you’re only applying a vertical load on the stud. The stud will only stretch on the vertical axis.
Fine thread vs. course thread: There are a lot of reasons to prefer fine threads over course threads. For any given size a fine thread is stronger than a course thread. This is true of both tension and shear. Fine threads are less prone to loosening from vibration because the thread incline is smaller. Finally a fine threaded bolt allows finer adjustments because of the smaller thread pitch.
Wheel Studs: This is the nut and bolt that gets removed and reused more than any other nut and bolt on your car. How long do these things last anyways? The better question is how much do you abuse your wheel studs. Impact wrenches, both air and electric, have destroyed more wheel studs than any other tool in the shop. Elastic deformation is the wheel stud’s ability to stretch and spring back to its original shape. The yield point is a situation where the bolt has been stretched past its elastic limit and can no longer spring back to its original shape. If a wheel stud is over-torqued, and stretched past its yield point it can no longer maintain the proper clamp load.
Over-torquing the wheel stud is common because so many people insist on using impact wrenches. Using an impact wrench to install wheels can cause the wheels to have three to five times the specified lug nut torque. The use of lubricants and anti-seize compounds on the threads can cause an even higher degree of over-torquing. You wouldn’t use your impact wrench when you install your cylinder heads. So why are you using it on your lug nuts?
