2023 ARP Catalog

19 A typical value for this reciprocating weight is in the vicinity of 20,000 lbs. For purposes of bolt design, a “rule of thumb” is to size the bolts and select the material for this application such that each of the 2 rod bolts has a strength of approximately 20,000 lbs. (corresponding to the total reciprocating weight). This essentially builds in a nominal safety factor of 2. The stress is calculated according to the following formula: so that the root diameter of the thread can be calculated from the formula: This formula shows that the thread size can be smaller if a stronger material is used. Or, for a given thread size, a stronger material will permit a greater reciprocating weight. The graph (see page 20) shows the relationship between thread size and material strength. It must be realized that the direct reciprocating load is not the only source of stresses in bolts. A secondary effect arises because of the flexibility of the journal end of the connecting rod. The reciprocating load causes bending deformation of the bolted joint (yes, even steel deforms under load). This deformation causes bending stresses in the bolt as well as in the rod itself. These bending stresses fluctuate from zero to their maximum level during each revolution of the crankshaft. The next step is to establish the details of the geometric configuration. Here the major consideration is fatigue, the fracture that could occur due to frequent repetition of high stresses, such as the bending stresses described above. Several factors “H” beam-deformed. Total translation contours. For loading in tension due to acceleration forces at 8000 RPM Motorsports Fastener Engineering for the Non-engineer FASTENER TECH