ARP started applying technology to race fastener design and manufacturing in 1968. We’ll discuss five components of fastener technology in detail.
Today’s critical diesel fasteners – head studs and bolts, main studs and bolts, and driveline – have been designed stronger than ever before to handle the extreme loads. As a result, installation pre-loads – the amount the fastener is stretched during installation – are very high.
There are three methods that can be employed to determine how much tension is exerted on a fastener; using a torque wrench, measuring the amount of stretch, and turning the fastener a pre-determined amount (torque angle). Of these methods, use of a stretch gauge is the most accurate.
The following material is intended to provide a brief overview of the metallurgical considerations that influence the design and production of the most reliable fasteners in motorsports. It is hoped that a simple understanding of the knowledge and commitment required to produce this reliability will make your future fastener decisions much, much easier.
The materials ARP uses in fastener manufacturing are listed and compared.
There are six types of metallurgical failures that affect fasteners. Each type has unique identifying physical characteristics. The following examples are designed to be used like a spark plug reading chart to help analyze fastener failures.
Set of 16 connecting rod bolts made from Custom Age 625 Plus
The S65 engine is a race inspired engine that is capable of tremendous operating speeds. With an 8400 RPM rev limit from the factory it is a very high strung engine. The engine is built “tight” from the factory and has become known to have rod bearing issues in which replacing the bearings is required to prevent complete engine failure.
When replacing the rod bearings it is critical to use new hardware when reinstalling the bearing caps. ARP’s connecting rod bolt set is made from Custom Age 625 Plus and is specifically engineered for the S65 V8. The material of these bolts has a high tensile strength and further improves upon a weak are of the S65 V8 engine.
When installing these ARP fasteners you must use ARP Ultra-Torque Fastener Assembly Lubricant to lubricate the threads of the bolt under the head of the bolt. ARP recommends the stretch method when tightening rod bolts