2018 ARP Catalog rev4

28 800-826-3045 FASTENER TECH The Lubricant Is The Key A major factor that influences friction in a fastener is the lubricant used, and therefore influences the torque required for a particular installation. One of the most overlooked aspects of choosing a fastener assembly lubricant is…the lubricant’s abil- ity to stabilize friction inherent in all high performance engine fasteners. As discussed earlier, friction is at its highest point when a new fastener is first tightened. This friction inhibits the fasteners ability to achieve the required clamp load on the first several cycles. In fact, ARP’s in-house Research and Development department has proven that new fasteners using motor oil and other commonly used lubricants such as Moly and EPL typically require 5-7 cycles before final torquing to level out the initial fric- tion and achieve the required clamp load. Slicker lubricants may reduce the required torque by as much as 20-30% to achieve the desired clamp load, but compromise in areas of major importance such as repeatability, and may yield the fastener prematurely. Typically, the slicker the lubricant, the greater the clamp load scatter will be during installation. The bottom line: clamp load repeatability and consistency from a fastener to fastener perspective, should be the number one consideration when choosing a fastener assembly lubricant. Remember even the best fastener is only as good as its installa- tion. Clamp load repeatability is the foundation for maintaining round housing bores, and consistency ensures the same clamp load from one fastener to another across a large area, such as the deck surface of a cylinder block. These two fundamentals are the cornerstone of every successful fastener installation and that’s why ARP’s engineering team set out to develop the “ultimate” fastener lubricant. The result of several years of extensive R&D is a remarkable assembly lube called ARP Ultra-Torque®. As shown in the graph above, ARP Ultra-Torque® clearly provides the clamp load repeatability and consistency that no other fastener assembly lubricant on the market today can provide. Fastener Surface Finish and Condition of Threads In addition to the lubricant used, friction is affected by the sur- face finish of the fastener itself and the condition of the threads. For example, black oxide behaves differently than a polished fastener so it’s important to follow the torque recommendations with each fastener kit. Then there’s the very real problem of burrs and debris in the bolt holes that can significantly affect the amount of torque required to achieve the recommended clamp load. All bolt holes should be thoroughly cleaned using thread chasers to clean the threads before installation. ARP offers these special cleaning chaser taps on page 128. Torque Wrench Accuracy It is possible for even the most expensive torque wrench- es to lose accuracy over time. Rough use or repeated loos- ening of fasteners using your torque wrench as a “breaker bar” will exacerbate the loss of accuracy. In fact, ARP field tech- nicians have seen a wide range of torque wrench reading errors as much as 15-30%. This just emphasizes the importance of treating torque wrenches with the utmost of respect and having them checked periodically for accuracy. The Torque Angle Method Since the amount that a bolt or nut advances on the thread per degree of rotation is determined by the thread pitch, it would appear that any amount of stretch in a given bolt or stud can be accurately predicted by measuring the degrees of turn from the point where the underside of the bolt head or nut face contacts the work surface. Termed the “torque angle” method, this proce- dure has long been the standard of civil engineering. It has been suggested that torque angle is a relatively simple and valid proce- dure to use in blind hole installations—where it is not possible to physically measure the actual bolt stretch. ARP has conducted extensive evaluations of the torque angle method, and concluded that – for high performance engine appli- cations – it is suitable only when calibrated for each installation. Our investigation has proven that installed stretch is depen- dent not only on the pitch of the thread and the degree of rotation, but also on the amount of compression of the clamped components, the type of lubrication, the length of the male fas- tener, and the amount of engaged thread. It’s important to note that for the same degree of rotation, the amount of bolt stretch will differ from aluminum to cast iron cylinder heads, or when installing a steel main cap on a cast iron or aluminum block. Furthermore, each length fastener requires a unique torque-angle to obtain the correct stretch for that fastener. The torque angle method can be accurate – but only if each individual application has been calibrated by direct measurement of bolt stretch. If you do employ the torque angle method, it’s best to begin calibrating rotation from some small measured torque rather than the first point of contact with the work face. To achieve optimum accu- racy, always use ARP Ultra-Torque® fastener assembly lubricant whenever possible. ARP’s computer-controlled torque-tension machine can apply a given torque or torque-angle to a fastener and measure the clamp load. Through test cycles, it is possible to chart the clamp load scatter with various fasteners and lubricants. EPL Moly Oil Torque Cycle 17,000 16,000 15,000 14,000 13,000 Preload in lbs 1 2 3 4 5 6 7 8 9 10 Torque Cycle 19,000 18,000 17,000 16,000 15,000 14,000 13,000 Preload in lbs ARP Ultra-Torque EPL Moly Oil 1 2 3 4 5 6 7 8 9 10 Torque Cycle 17,000 16,000 15,000 14,000 13,000 12,000 Preload in lbs 1 2 3 4 5 6 7 8 9 10 Oil Moly EPL Installation Clamp Load Scatter Comparison (Target Preload 18,000 lbs @ 120 ft-lbs)