Thousands of studs await the heat-treat process.
For those of you who think race car technology takes a back seat to aerospace, this article may surprise you. If you think the options for fasteners are either a Grade 5 or Grade 8 bolt, well, you really have something to learn. And if you're serious about racing, quality fabrication, and engine building, you must read this article.
Racing fasteners are just that-nuts, bolts, screws, and studs that hold the race car together. How well they do that will make the difference between winning and losing races, and will determine whether your engine and other important components can withstand the severe conditions of racing: large load demands, high and changing temperatures, vibration and harmonics, and cycling of stresses. By obtaining proper fastener performance, costly repairs can be avoided that could result from the use of lower quality fasteners or incorrect applications.
To get the lowdown on fastener technology, we went to the king of race car fasteners: Automotive Racing Products (ARP). For more than 30 years, this company has been one of the industry's pioneers in adapting state-of-the-art materials and manufacturing technology to the motorsports market. From NASCAR, NHRA, Formula 1, and IndyCar, to late-models and go-carts, ARP is heavily represented in every type of race car fastener.
Types of Fasteners
To be sure, race car fasteners include all bolts, studs, nuts, and connecting hardware within the engine-nowhere else will you find the extreme loads put on such critical pieces. Although there are basic applications of fasteners used for holding automotive components together-such as air-cleaner studs, water-pump bolts, valve-cover bolts, wheel studs, and body hardware-the real magic of technology shows itself in the important connections of items like rocker-arm adjusters, head and main studs and bolts, and the most critical of all connecting bolts: rod bolts. This is where a single failure could not only cost the race, but also result in wasting a $20,000 to $50,000 engine.
ARP's cold-forging machines perform five quick operations faster than you can blink an eye
"The application of fastener requirements to race car engines is unique," says Robert Florine, vice president of ARP. "Unlike most aircraft fastener connections, where redundancy is part of the design criteria, each connection within the racing engine is basically the weakest link. If a rod bolt breaks, that engine is history-it will probably fail catastrophically. In aircraft, even in the engines, a (fastener) failure should not lead to a catastrophic failure. There is a lot of overdesign in aircraft."
"Race cars don't have that luxury. A single failure can end the race and be extremely costly. That is why the quality of fasteners and their correct application is critical to good engine building and proper fabrication of the car. Connection failures cannot be an option in racing, and to eliminate failures it takes a good understanding of each important connection, the fastener requirement, and correct installation and maintenance."
Not every connection requires the quality of a fastener used in rod bolts and other high-stress applications. Chassis fasteners, for example, may need only the amount of strength required for a single bumper impact. The key to selecting the proper type and grade of fastener is to know the type of loading the fastener will endure and the rate, in cycles, it will encounter.
Loading of Fasteners
Two basic types of loading occur in fasteners: shear loads and tension loads. Many chassis bolts and studs are put under shear loads. This occurs when two forces move laterally in opposite directions-the bolt or stud is in shear tension. Fasteners such as these infrequently see material structure failure; it is not difficult to engineer good-quality bolts and studs that can withstand tremendous levels of shear loading. Drive-plate bolts and wheel studs are good examples of fasteners operating under shear loading.
The other loads that fasteners see are tension- and, to a lesser extent, compression-loads. In the case of a connecting rod bolt, for example, the bolts are continually being stretched (once for every cycle the bolt material is put in tension), then the material is relaxed. Combine this severe tension loading with hundreds of thousands of cycles, and you can begin to appreciate the physical requirements of fasteners operating in these extreme circumstances.
Because of the different loading requirements on a fastener, many different grades of materials are used. In fact, four grades are generally recognized in fastener manufacturing: commercial, aircraft, CHQ (cold head quality), and SDF (seam- and defect-free). SDF is typically the highest-grade steel available and is what ARP uses. The use of different materials will provide bolts with strengths ranging from 120,000 psi (tensile strength) all the way up to 300,000 psi. With that type of variance in strength of fasteners, understanding use and load requirements is essential.
Quality ProductionPrevents Fastener Failure Incorrect application and/or installation is the result of 80- to 90-percent of fastener failures, says Florine. That's a high figure, but after a tour of the operations of ARP, you begin to realize why manufacturing or material defects are essentially nonexistent. Except for the purchase of specialty premium-grade wire from the best mills in the country, ARP completes 100 percent of the manufacturing in-house (actually, ARP has four different plants for production). That's everything from cold and hot forgings to heat-treating, to machining, and finally, plating. There is a good reason why ARP chooses to have complete production control.
"There are many steps to making superior-quality fasteners, which start from proprietary steels with extremely high tensile strengths and proceeds with up to 20 or 30 separate operations," says Florine. "Each step has to be closely monitored to ensure exact tolerances. For example, heat-treating is critical to bolt strength. We found that we could not get the consistency we required from outside sourcing, so we brought complete heat-treating equipment in-house. That's not an easy thing to do, but it is part of our dedication to making the finest quality fasteners available."
Testing is an integral part of fastener development and production consistency. Whether it's an initial design or just sampling a production run, ARP pushes the limits on fastener strength. It's one of the things that separates race car fasteners from aircraft fasteners. Most aerospace industry standards set test standards at 120,000 cycles. ARP will test bolts until they break. That can mean running bolts through millions of cycles.
Great emphasis is put on discovering why a fastener fails in use, and often a broken fastener can lead to the discovery of another problem.
"When we see a failed connecting rod bolt, for example, we must look at everything to discover what caused the bolt to break. Most often that broken bolt will lead to what caused it to break, such as a lack of oil for lubricating the piston. Obtaining the real cause of a broken fastener requires that we look at all the related components. Essentially, we must solve the puzzle to find the real reason for a problem."
ARP is not the only company making quality fasteners, but its diversified product line allows them to be uniquely specialized in all areas of race car fastener production. This has led to some unique answers when faced with real racing problems.
Troubleshooting fastener problems are what every fastener manufacturer must face. Making engines and race car parts lighter, faster, stronger, and more reliable requires constantly upgrading performance. For fastener manufacturers, that means solving problems posed by the racing industry.
Only premium-grade steel is used in all of ARP's fasteners, many of which are proprietary.
In the early '80s, Buddy Baker lost his chance to win at Daytona due to a broken wheel stud. The problem was brought to ARP's attention for a solution to the stud problem (the company did not manufacture the broken stud). Upon examination, even new studs showed cracks at the root of the thread. ARP addressed the problem by starting with the toughest design criteria. It calculated the load on the right-front wheel studs of a car (the most-loaded tire) running at Daytona at 200 mph (before restrictor plates), and designed a stud so one stud alone could hold the wheel. That required a new material for higher strength. ARP also added the now-common bullet-tip end and large-diameter lead-in to make cross-threading virtually impossible. Finally, the company applied a baked-on lubricant, which significantly speeded up pit stops (up to two full seconds). The result was a big step in safety and performance, and a tribute to ARP's philosophy of designing fasteners for their specific applications.
In another case, ARP's final solution to a head-cracking problem was the development of a stud kit that incorporated four different-diameter studs, two different materials, and three different tensile-strength levels. The solution was complex, but the problem was solved.
Whether it be a Winston Cup wheel stud, a late-model rocker-arm adjuster, or a head stud, fastener manufacturers strive to build the best piece for a specific application. But manufacturing the fasteners is one thing. Their proper use and installation are another.
Knowledge Is King
"Understanding how fasteners perform optimally is absolutely essential for a race team-too many things are riding on the quality and performance of fasteners. Engine and chassis performance, race results, costs, and most importantly, safety, are all at stake when choosing and installing fasteners," says Florine.
Robert Florine shows off part of ARP'sin-house heat-treating plant. Correct heat-treating
Ironically, it is probably more difficult for the Saturday-night racer to understand all the technology and applications than a Winston Cup crew member. At the Cup level, each crew member has a specific area of expertise: engine, drivetrain, suspension, and so on, and his concentration is in one area only. But for most racers, the crew chief and driver must often be aware of every application, since they are involved in virtually every facet of the car's operation. How does one learn all there is to know about all these fasteners, as well as their correct application and installation?
The answer: knowledge and experience. Like everything else in racing, information is the key to knowing how to get the most out of your equipment.
"We are always providing information to racers through trade shows, seminars, our catalog, and our tech line. It is in our best interest to educate racers to the highest level possible," says Florine. "Fasteners are cheap insurance. Their proper use is essential to quality race cars."
The knowledge it takes to become an expert in fastener technology and application would take a complete book to present, but Florine had these important points to make in choosing fasteners and installing fastener hardware:
First, get the proper fastener for the proper application. That means you don't underkill or overkill the fastener application. Having a fastener that can't meet strength demands can have obvious ramifications, but having ones that don't tighten properly (require extreme torque to tighten), for example, can lead to crushing the base material (aluminum). Each connection on a race car has its own performance requirements, and each fastener must be chosen to meet those requirements.
Inspection and testing are part of the ongoing quality control at ARP. The instrument hold
Second, use a good quality lubricant. Many tension fasteners must be lubri-cated to achieve proper tension strength for the bolt. Motor oil is one good lubricant, but ARP makes a special moly lube for properly preloading bolts. Properly seeding and preloading bolts ensures that the backup torque value (that which is required to loosen the bolt) will be as close as possible to the bring-up (tightening) torque value. That will prevent any possibility of loosening problems due to vibrations and harmonics. Consult ARP or a qualified speed shop for more information on this.
Third, make sure bolts and nuts don't bind when handtightening. Any undue friction when tightening means there is an obstruction, causing a false preload condition. Clean parts and retap threads if necessary.
Fourth, for most tension-loading applications, don't use locking devices. They prevent proper preloading to take place. Due to heat and vibration, the locking mechanism is subject to change and could result in a loosening of the bolts. Properly torqued bolts will withstand all the changing dynamics of a bolt or stud application. Note: It is essential to have a thorough understanding of proper torque values for a given bolt in a given application. Obtain a torque table from ARP or other fastener manufacturer, and when in doubt, contact the company for expert advice.
Finally, do the research necessary for complete fastener information. That knowledge and its application might save you a race car or engine someday-not to mention a heap of money.