I have multiple rod/piston mockups to do on a 360. will multiple torqueing/removeing/retorqueing rod nuts cause an integrity problem with them? I heard once where useing old rod nuts for this is a good plan (easier on the threads). I think these are aftermarket rod bolts. thank you for your time.

I have to wonder why you need to torque the nuts if all you are doing is mock-up. Also, recall that when you torque a bolt/nut that the bolt will stretch. Perhaps repeated stretch cycling should be avoided.
If you really need a tight bolt/nut you could use an old oem part.

As long as you do not exceed the elastic limit of the bolt or nut you can torque and retorque forever. Torque to yield bolts are designed to exceed that limit and should not be reused. I have never heard of a rod bolt being TTY.

Not a problem. there are some that believe cycling the nut on a bolt several times before final torque makes for a more accurate torquing in the end. I dunno if this is because they think it burnishes the threads or what, but it isn't an issue regardless.

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.

Alright I will torque em to spec the several times I need to & not sweat it (& might be beneficial) & Wayfarers' point is well taken that if full torque IS a problem then why the need to max out on the mockup checks. thanks guys.

You don't want to use other nuts on the rod bolts. Also put the nuts on the same rod bolt in the same direction every time, don't put them in a box and mix and match nuts.

Noted & actually way back I had heard that maultiple torqueings weakens the thread fit & I'm surprised to find it is the other way around. speaking of the stretch gauge, where do you go to find out how many thousands you want it to get stretched to? EDIT & think these ones I'm dealing with here are flanged so at least that part is taken care of & I will keep em on the same bolt.

To the bolt manufacturer. There will be little intents in the head and end of bolt if a stretch gauge is to be used on that bolt.

Good stuff bro, I had no idea!

More than one machinist told me this. Makes sense to pull the threads the same direction on the same pieces.

Others say it doesnt matter. Use your best judgement.

Nanket I am gonna (religiously) do that from now on. that does make good sense when you think about it. Now all I gotta do is fix the leaking head gasket from Hell.