Correct installation of ARP fasteners—particularly connecting rod bolts and main studs—is essential for ensuring the performance, safety, and longevity of high-performance engines. These fasteners are designed to endure extreme forces and must be handled with precision to avoid mechanical failure. The following article draws on official installation instructions, technical evaluations, and best practices from ARP documentation and related discussions to provide a comprehensive guide to ARP fastener installation.
Overview of ARP Fastener Installation
ARP (Automotive Racing Products) is a leader in the design and manufacturing of high-performance fasteners. Its products, including connecting rod bolts, head studs, and main studs, are engineered for high-stress environments in racing and high-horsepower engine applications. Correct installation is crucial not only for performance but also for the safety of the engine and the operator.
ARP fasteners are available in various materials, including 8740 chrome moly, stainless steel, and exotic alloys used in aerospace applications. These materials are selected for their strength, durability, and resistance to fatigue under repeated loading.
The installation process for ARP fasteners typically involves the use of specialized tools such as stretch gauges and torque wrenches. Proper lubrication is also a critical factor in achieving consistent and accurate preload. ARP recommends the use of its proprietary lubricant, ARP Ultra-Torque®, to ensure the most consistent and repeatable results.
Installing ARP Connecting Rod Bolts
Connecting rod bolts are among the most critical components in an engine. These bolts must withstand immense forces generated during engine operation, and improper installation can lead to catastrophic failure. ARP provides detailed instructions for installing its connecting rod bolts, with a strong emphasis on using a stretch gauge to measure bolt elongation.
Preparation and Installation Steps
Disassemble and Clean Components: Before beginning installation, it is important to clean the connecting rod and all associated components. This includes removing any rust preventative and ensuring that the threads on the bolts and rod beam are free of debris.
Apply ARP Molylube: ARP recommends the use of ARP Molylube on the threads and under the head of each bolt. This lubricant helps to reduce friction and ensures consistent torque readings.
Assemble the Rod to the Piston: Care must be taken to align the rod bearing notches with the intake side of the engine, due to the crankshaft's rotational direction. Each rod is numbered, and the same number must be present on both the cap and the beam to ensure proper alignment.
Install the Bolts Properly: Bolts should not be used to pull the cap into position. Instead, the cap and beam should be tapped into alignment first. Once aligned, the bolts can be installed and tightened to the correct specifications.
Monitor Bolt Stretch: ARP strongly advises using a stretch gauge to measure bolt elongation. This is considered the most accurate method for measuring preload. The recommended stretch values vary depending on the bolt type and size.
Torque and Stretch Specifications
ARP provides detailed specifications for the stretch and torque values of its connecting rod bolts. The following table summarizes the key data from ARP documentation:
| Type | Size (Inch) | Size (Metric) | Stretch (Inch) | Stretch (mm) |
|---|---|---|---|---|
| ARP 2000 | 5/16" x 1.500" | 7.9mm x 38.1mm | 0.0056" | 0.14224mm |
| ARP 8740 | 3/8" x 1.600" | 9.5mm x 40.64mm | 0.0047" | 0.11938mm |
| ARP 2000 | 3/8" x 1.600" | 9.5mm x 40.64mm | 0.0058" | 0.14732mm |
| ARP 8740 Wave Loc | 3/8" | 9.5mm | 0.0063" | 0.16002mm |
These values should be used in conjunction with a stretch gauge for the most accurate results. If the bolts show a permanent increase of 0.001" or more in length after installation, they should be replaced due to potential deformation.
Installing ARP Main Studs
Main studs are another critical component in engine assembly. These studs secure the main bearing caps to the engine block and must be torqued correctly to ensure the engine runs smoothly and safely.
Challenges in Obtaining Main Stud Instructions
One user noted that the main stud instruction sheet was missing from a recent shipment of ARP parts. This highlights the importance of retaining official installation instructions. ARP has a generic torque chart that includes torque values for various fastener types, but these values should be used with caution. For example, ARP recommends a torque value of 90 ft-lb for head studs. However, it is important to note that the load a stud can handle is significantly higher than the load the engine block can sustain, meaning that over-torquing can cause damage to the block or other components.
When using a torque wrench, it is important to understand that the friction factor changes with each cycle of tightening and loosening. This means that initial torque readings may not be consistent with subsequent readings. To ensure accuracy, it is recommended to use ARP Ultra-Torque® lubricant, which provides more consistent results and reduces the impact of friction variability.
The Importance of Calibration and Lubrication
ARP has conducted extensive evaluations of the torque angle method, which involves tightening a bolt to a specific angle after reaching a certain torque value. While this method can be effective, it must be calibrated for each specific application. Factors such as the pitch of the thread, the degree of rotation, the type of lubrication, and the amount of engaged thread all influence the amount of bolt stretch. For example, a bolt installed in an aluminum cylinder head will stretch differently than one installed in a cast iron head. This is why ARP recommends beginning calibration from a small measured torque value rather than from the first point of contact with the work surface.
ARP Ultra-Torque® is a key component in achieving consistent and repeatable results. It was developed through years of research and testing and is designed to provide the best combination of preload repeatability and consistency. These two factors are essential for maintaining round housing bores and ensuring the same preload across all fasteners in a large area, such as the deck surface of a cylinder block.
Material Grades and Quality Control
ARP uses a wide range of materials in its fasteners, including stainless steel, 8740 chrome moly, and exotic alloys used in aerospace applications. These materials are selected based on their mechanical properties and ability to withstand the stresses of high-performance engine operation.
For example, 8740 chrome moly is available in four grades, but ARP uses only the first two (SDF and CHQ), which are of higher quality and more expensive than the standard "Aircraft" grade. This decision reflects ARP’s commitment to quality and performance.
In addition to material selection, ARP follows rigorous quality control standards, including ISO 9001-2000. This system is well suited for manufacturers with engineering design functions, drawing control, and statistical techniques to achieve demanding quality requirements. It is the foundation of ARP’s World Quality Concept, which ensures that every fastener meets the highest standards of precision and reliability.
Common Installation Issues and Best Practices
Under-Torquing and Over-Torquing
Two of the most common causes of failure in connecting rod bolts and other fasteners are under-torquing and over-torquing. Under-torquing results in insufficient preload, which allows the alternating load to impose cyclic stress on the bolt. This can lead to fatigue failure over time. Over-torquing, on the other hand, can cause the bolt to be stressed too close to its yield point, increasing the risk of immediate failure.
To avoid these issues, it is essential to use the correct torque values and to verify the results using a stretch gauge or torque wrench. ARP provides detailed torque specifications for each fastener type and recommends that users maintain a record of all measurements taken during installation.
Lubrication and Reuse
ARP Ultra-Torque® is specifically formulated for use with high-performance fasteners and is recommended for all ARP installations. Its unique properties help to reduce friction and ensure consistent torque readings. Users are advised to apply a small amount of the lubricant to the threads and under the head of each bolt before installation.
It is also important to note that ARP does not recommend reusing bolts unless they have been inspected and measured for stretch. If a bolt shows a permanent increase in length of 0.001" or more, it should be replaced. This is because even a small amount of deformation can significantly reduce the bolt’s strength and increase the risk of failure.
Conclusion
Proper installation of ARP fasteners is essential for the performance, safety, and longevity of high-performance engines. Whether installing connecting rod bolts, head studs, or main studs, it is important to follow ARP’s detailed instructions and to use the appropriate tools and lubricants. The use of a stretch gauge is highly recommended for achieving the most accurate results, and users should be aware of the potential risks associated with under-torquing and over-torquing.
By following these guidelines, users can ensure that their ARP fasteners are installed correctly and that their engines operate at peak performance for years to come.