By Ron Ceridono – Photos by Brian Brennan, Ron Ceridono & Courtesy of ARP
For those who have been playing with hot rods as long as the editorial staff of Modern Rodding, there are countless tales of woes resulting from youthful ignorance. Take the time a buddy of an unnamed impressionable lad used all-thread to replace two missing main bearing bolts in a Flathead Ford. The results were not pretty. Gary Holzapfel also bore witness to fastener failure, seeing catastrophic failures in various race engines, albeit for far less ridiculous causes than what a clueless kid created. Holzapfel saw a need for quality fasteners and used his aerospace background to create Automotive Racing Products (ARP). Today, ARP’s line of products includes virtually all the fasteners found in an engine or driveline, ranging from high-quality OEM replacement parts to specialty fasteners used in every form of racing on land or water.
One of the reasons for ARP’s success is the complete control of the manufacturing process and the use of the best materials. ARP notes, “The alloys employed in manufacturing fasteners come in various grades; ARP uses only the purest grades, which are superior to commercial and aircraft-quality material. All heat-treating is done in-house (as are all manufacturing operations) to ensure reaching the proper strength level, with special racks used to guarantee precise, even penetration. Threads are rolled (not cut) after the heat-treating process for superior (up to 20 times better) fatigue life.”
When it comes to replacing fasteners, the experts at ARP explain that it’s done for various reasons. Chief among them are age, stress, hydrogen embrittlement, and corrosion. They also point out that critical fasteners like rod bolts stretch a certain amount when the desired torque is reached. Given the number of cycles rod bolts endure, replacing them during a rebuild makes good sense; the same applies to head bolts. ARP has tested nearly every fastener used in popular engines manufactured from the 1950s to the present—even flathead V-8s going back to the ’30s—and has developed high-performance replacements. There are thousands of special kits in ARP’s catalog, all designed to be reused.
Many contemporary engines use torque-to-yield (TTY) fasteners. These fasteners are torqued to a prescribed value then tightened further by turning them a specified number of degrees to stretch them. ARP notes that while TTY fasteners are suitable for OEM applications, additional stress from engine modifications can cause them to fail. For that reason, and because reusing these fasteners is not generally recommended, ARP has developed replacement bolt kits for engines with TTY fasteners, each with application-specific torque specs.
A common question asked of ARP’s factory tech representatives is, “Which are better, bolts or studs?” The answer is, “It all depends on the application.” For stock to mildly modified street engines, ARP head bolts are more than adequate. Once the argument for bolts over studs was that for street-driven vehicles with many accessories in a tight engine bay bolts made it easier to remove the cylinder heads with the engine in the car. However, ARP studs are hex broached on the ends, making them just as easy to remove as bolts, so there’s no real downside to using them. Additionally, studs offer several advantages—they simplify head and main cap installation and, in performance applications, provide more consistent torque loading. As the ARP tech guys explain, “When you use bolts, the fastener is actually being ‘twisted’ while it’s being torqued to the proper reading. Accordingly, the bolt is reacting to two different forces simultaneously.” When a stud is properly installed (hand-tight), as the nut is torqued, the stud will stretch only along the vertical axis, thereby applying an even clamping force.
ARP emphasizes the importance of properly tightening fasteners of all types. They note that general torque recommendations are only guidelines; following the specific torque instructions provided is essential. Another key factor when torquing fasteners is the use of appropriate lubricants. Using oil, moly, and common assembly lubricants can lead to what’s called “preload scatter,” which means different torque amounts on adjacent fasteners.
ARP’s Ultra-Torque provides consistent and repeatable torque readings during assembly and helps prevent corrosion. Since head gaskets may compress during installation, always consult the gasket manufacturer to determine if retorquing is necessary.
When it comes to rod bolt torque specifications, they are critical. ARP tells us a typical 3/8-inch small-block Chevy rod bolt must be stretched between 0.0055 and 0.0060 inch to achieve the approximately 10,000 pounds of preload required. Of course, the most accurate way to measure that is with a stretch gauge, which is usually only found in high-end race shops. As a result, in most cases, a torque wrench becomes the tool of choice when tightening rod bolts, which requires some consideration. First and foremost, a proper lubricant must be used; ARP specifies Ultra-Torque. Second, it’s essential to follow the rod bolt stretch/torque specifications provided with the bolts (found in the ARP catalog). Third, ensuring the torque wrench is accurate is important. Maintaining accuracy involves returning the torque wrench to 0 after use and never using it as a breaker bar to remove fasteners.
Along with all their high-performance fasteners, ARP also offers show-quality engine and accessory fastener kits for all popular engines. Virtually everything you need is labeled and organized in one convenient package. Kits are available in black oxide finish chromoly steel or polished stainless; both are available with hex or 12-point heads.
In addition to engine kits, ARP offers bolts in packages of 5 in standard sizes from #10 to ½ inch and metric sizes from M6 to M12; matching nuts and washers are also available. When it comes to holding your hot rod’s engine, driveline, and suspension together, ARP has all the nuts and bolts it will take. MR
Check out this story in our digital edition here.
