ARP 2017 Catalog r3

28 800-826-3045 FASTENER TECH The Lubricant Is The Key The main factor in determining friction in a threaded 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 ability to “control” the normal function of friction inherent in all high performance engine fasteners. As discussed earlier in this section, friction is at its highest point when a new fastener is first tightened. This “friction” inhibits the fasteners ability to achieve the required preload 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 friction and achieve the required preload. Slicker lubricants may reduce the required torque by as much as 20-30% to achieve the desired preload, but compromise in areas of major importance such as preload repeatability, and may yield the fasten- er prematurely. Typically, the slicker the lubricant, the greater the “preload scatter” or preload error there will be during installation. The bottom line: Preload repeatability and preload consisten- cy 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 instal- lation. Preload repeatability is the foundation for maintaining round housing bores, and preload consistency ensures the same preload 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 new assembly lube called ARP Ultra-Torque®. As shown in the graph above, ARP Ultra-Torque® clearly provides the repeatability and preload consistency that no other fastener assembly lubricant on the market can provide today. For more information on ARP Ultra-Torque® see page 121 . Fastener Surface Finish and Condition of Receiving Threads In addition to the lubricant used, friction is affected by the surface finish of the fastener itself and the condition of the receiving 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 sig- nificantly affect the amount of torque required to achieve the recommended preloads. All bolt holes should be thoroughly cleaned using special “Chaser Taps” to optimize the threads before installation. ARP offers these special cleaning chaser taps on page 123. 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 accura- cy. In fact, ARP field technicians 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 pro- cedure has long been the standard of civil engineering. It has been suggested that torque angle is a relatively simple and valid procedure to use in “blind” 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 dependent 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 fastener, and the amount of engaged thread. It’s important to note that for the same degree of rotation, the amount of bolt stretch will be criti- cally different between an aluminum or cast iron cylinder head, or when installing a steel main cap on a cast iron or aluminum block. Furthermore, there is a significant difference in stretch between the long and short cylinder head bolts or studs on the same head. The torque angle method can be accurate – but only if each individual application has been previously 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 accuracy, always use ARP Ultra-Torque ® fastener assem- bly lubricant whenever possible. ARP’s computer-controlled torque-tension machine can apply a given “torque” or “angle” to a fastener and measure the actual preload. Through test cycles, it is possible to chart the “preload scatter” with vari- ous 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 Preload Scatter Comparison (Target Preload 18,000 lbs @ 120 ft-lbs)