Nervous about ARP Rod bolts, used a stretch gauge

[Kemo]

All,

I just got finished installing the rods on my SC's crank. I used the Summit Racing stretch gauge. The ARP instructions clearly stated that if I didnt have a stretch gauge to just torque to 50 ft/lbs using the ARP thread lube. Out of curiosity, I just wanted to know how much the bolt would stretch as i got up close to 50 ft/lbs. So I set my torque wrench to 40 ft/lbs, tightened up a bolt and noted that it moved about .004" (about 4 ticks on my gauge). So I kept going in 2 ft/lb increments till i got to 50 ft/lbs. At 50 ft/bs, the stretch was only at .005". I quit keeping track and tightened until i got to the .0095 to .010 which took a bit more work to get there.

Others have mentioned that the actual torque is not the important part but rather the stretch. I just want to get some verification here because im pretty sure the total torque it took to stretch to .010 is north of 60 ft/lbs.

Did i ruin my ARP rod bolts?

Thanks for any input.

[RedCoupe]

Did you write down the initial measurement of the bolts before you stretched them? If they return to the original dimensions when you loosen them, then you are fine. ARP says their bolts may be reused. The only concern is when a particular bolt doesn't return to the original dimension, or even close.

[Jonny042]

Stretch is a better indicator and is more trustworthy than torque.

I checked my torque against stretch on those same bolts and found it to be predictable and close to 50 ft/lbs.

Did you lube the threads and bottom of the nut well with the ARP Lube? It's also possible your torque wrench is out of whack.

[patkeefe]

In the world of stress and strain, ARP (and Raceware) want you to stretch a bolt to close to the "plastic range", where stretch is irreversible. I have called them and spoken to the engineering staff. The result was that if you get half as much stretch, for example, you get almost as much strength out of the fastener.

The only way to know if you screwed up the fasteners is to compare the length to the original length before stretching. Plastic range means they won't come back-they exceeded the yield strength. That's probably why they say 50 ft-lb; it is a safe stretch.

Light reading:
https://en.wikipedia.org/wiki/Stress–strain_curve

The good news is that you likely didn't pass the ultimate strength.

[jons911]

I ran into a similar issue when I was installing my Carrillo rods. They are set by stretch but have a max torque. I wasn't getting quite to the recommended stretch at the max torque, so I called Carrillo and asked whether I should use the torque or stretch as my limiting factor. They told me stretch, as I expected, is what matters and the bolts can take way more torque. Based on the measurements I had, he recommended I go up another 8 ft-lbs or so to be in range.

I would venture a guess that ARP hardware is very similar. As long as you remain in the elastic range for the material, which the stretch range provided by ARP should do for you, the torque isn't that big of a factor.

[Jeff Alton]

Well known that ARP bolts take more than spec torque to attain the stretch measurement. You will be fine.

[1979-930]

The friction of the nut, washer and threads is inconsistent and causes torque values to vary from bolt to bolt on everything.
That’s why stretch is the proper way to measure.


Sent from my iPhone using Tapatalk

[Kemo]

thanks for the input! I used the ARP thread lube only on the threads, not on the entire bolt. All of mine are at or about .010 in stretch and believe it or not, you could feel when they got real close to that. Its like everything just stopped moving. id say at about .008, you could tell it was like an exponential change in the force needed to move just a little bit. And that is what worried me. But it seems like im on the right track. These were new bolts from EBS that came on the rods after a standard Rod reconditioning service.

[T77911S]

i will be doing this in the future.

so what would be the best way to go about this.
torque them to 50lb then start angle torqueing them and checking thing for stretch say every 45 degrees or so?

the reason I say angle torque is when I did my rear bearings on my 930 (crush sleeve) after torqueing to 320 I found that if I angle torqued past that I was able to get the sleeve to crush and get it to spec.

[boyt911sc]

Originally Posted by T77911S

i will be doing this in the future.

so what would be the best way to go about this.
torque them to 50lb then start angle torqueing them and checking thing for stretch say every 45 degrees or so?

the reason I say angle torque is when I did my rear bearings on my 930 (crush sleeve) after torqueing to 320 I found that if I angle torqued past that I was able to get the sleeve to crush and get it to spec.

Ty,

Use torque and stretch gauge at the same time and compare your data. To play safe you must have a “control gauge” in case something happens to your stretch gauge and affected its calibration. I use an Excel spreadsheet and took 3 measurements:
a). Initial measurements of the bolts (3x) and calculate the average.
b). Apply 30 ft.lb. torque and take measurements (3x). Tabulate.
c). Adjust torque wrench to 40 ft.lb. take measurements. Tabulate.
d). Adjust torque wrench to 50 ft.lb. take measurements. Tabulate.
NOTE:
Apply the supplied lubricant as per instruction from the manufacturer.

In some of engine rebuilds that I used ARP bolts and the above procedures, I had about 9 out 10 bolts within the spec and a few bolts very close to the lower value after the final 50 ft.lb application. The key to this task is using a good and well calibrated torque wrench to obtain consistent values.

Tony

[gtc]

I used a torque adapter from napa (example here) and a beam style torque wrench while also using a stretch gauge.
This method required an extra pair of hands, but made it easier to record stretch and torque at the same time, without switching back and forth between tools.

[911pcars]

Don't confuse torque specs for typical threaded fasteners. Those specs are designed to stretch the fastener a set percentage to create a preload on the joined materials.

Torque-to-yield fasteners are used in some applications to ensure a more accurate torque that includes stretching fasteners into their plastic deformation range and thus shouldn't be reused. Torquing and torque-to-yield are not the same.

Instead of using random suggestions, I would consult with the manufacturer for their recommendations and specs. For example:

https://arp-bolts.com/p/faq.php
https://www.counterman.com/torque-to-yield-fasteners-where-theyre-used-and-why-they-need-to-be-replaced/

A talking head describes tightening with a torque wrench and stretch gauge:
https://www.youtube.com/watch?reload=9&v=_Uhul4DmWuw

Sherwood