Supercuda's first sentence is exactly right. As a matter of fact, Blazin' Bob's memory is right too as ARP suggests torqueing new rod bolts a number of times, IIRC 3 times, to burnish the threads.

This all points back to the major problem of torqueing fasteners, which is the wide range of coefficients of friction possible between nut and stud. This results in one never being exactly sure of how much force the stretched stud is exerting on the joint. And the main reason to torque fasteners is to provide enough clamping force. Torquing is an inexact method, but one that can be understood and automated.

Measuring the bolt or stud stretch is the real way to determine the clamping force. There can be no question about that. Fasteners of critical joints in hydro plants, like main shaft coupling bolts, are usually tightened with stretch being the only value measured. When you reach the specified stretch you know what clamping force is being exerted. There is also a method that measures stretch indirectly, by heating the bolt to a specified temperature, then turning it until snug.

Torque to Yield (TTY) fasteners are a more precise way of tightening fasteners than torqueing. TTY depends on the yield strength of the bolt being constant from bolt to bolt. This is not hard for a manufacturer to do. The cross section of the bolt is known, the bolt is torqued to a minor value, then the bolt head or nut is turned a specified number of degrees. This has been calculated to be the number of degrees it takes to put the bolt or stud into its plastic region, stressing the fastener past its yield point. The curve after the yield point continues rising after a certain amount of yield, so it is necessary to limit the amount of yielding. This process is easy to automate and allows the manufacturer to tighten the fastener more accurately.

As I have pointed out before, my Mercedes M110 engine has torque to yield rod bolts which are definitely reusable. There is a necked down section and as long as it exceeds a certain diameter, the bolt can be reused. This is from the factory service manual.

R.