Fabulous

Hello all,
I bought the ARP2000 rod bolts and tightend them with stretch gauge to 0,001inch as recommended. Unfortunately I recognized that due to a weak spring in the gauge I got some inaccurancy. I made several try outs and came to the conclusion that due to that inaccurancy the stretch is somewhere between 0,0009 and 1,0012. tolerance is defined with 0,001-0,00105. So the question whether I can stay as it is or to scrap all bolts.
Any recommendations?
Thanks and regards
Fabian

Noah930

I don't know the answer to your question, but doesn't ARP have a technical.assistance line staffed by engineers to answer this type of question?

Igooz

It is always wise to acccurately measure the length of any critical bolt before you stretch it.

If you have done that very accurately, then proceed and can remove the rod bolts that you think were (slightly?) over-stretched. If in free-standing they return to their exact length prior to the stretch, you can use them again. You only want to do this once or twice, that's it. If they are stretched, then they are toast and not worth it.

If you did not measure them at the starting point, then you should take the safe path and replace all the ones that were over stretched.

When stretching rod bolts, you will need to make sure that you are using the correct lubricant. ARP makes their own versus engine oil or other internet snake oil.

It has been a while for me, but check your numbers. 0.001" is too small a stretch to me.

Fabulous

Yes you're right. I typed in wrong values. correct stretch is 0,01-0,0105 inch.
Unfortunately I did not measure each bolt before assembly so I cannot evaluate if the bolts have stretched or not.
ARP didn't answer the question yet and I cannot find any analysis how much a bolt at 0.01 stretch is stressed. A stress strain diagrams would help but I cannot find for ARP2000 material.
I think the tolerance can be greater than 0.01-0.105inch because when you just torque it to 40ft/lbs (value from ARP) the stretch tolerance will be much higher and the bolt will also work in the engine, right?

Igooz

If you are torquing to 40 lb/ft, then you better make sure that your torque wrench is 100% accurate and calibrated. And don’t forget the lubricant part as it throws off the reading.
Accurate stretch measurement is the best way for rod bolts although I know that for a 100 years people didn’t do it that way. ARP and similar companies view their material property as proprietary and will not share.

So, if I understand correctly, you stretched up to 1” instead of 0.01”? Or is it 0.0105” vs. 0.01”? I really cannot tell from your description. If you have stayed within 10% of allowable stretch then you are ok. If you think that you are more than that, then replace the bolts with new and proper lubricant and do it over. stress vs. strain curves are linear until you hit yield strength and it goes (almost) flat. I am guessing that ARP will handle my 10% rule easily.

Fabulous

Hello Igooz,

sorry for confusing...so ABP recommends a stretch value of 0.01-0.0105inch. I torqued my bolts with the stretch gauge to 0.01inch. But my stretch gauge has some reading-tolerances though handling. I made some statistics and came to the result that actually my bolt stretches vary from 0.009 - 0.012inch.
So that means that my bolts could have slightly more or less stretch than recommended and I'm questioning myself if it's still ok. Even if you lubricate your bolts well, torquing with just a torque wrench will result in higher tolerances than my 0.009-0.012inch or am I wrong?

Regards
Fabian

Igooz

OK, thank you for spelling it out for me. And it looks like you wan to do this by the book.

1. You are correct! Lubrication will throw off the torque reading evenif you use the lubricant that the fastener supplier recommends. I would recommend using ARP's lube, unless you have your own empirical data from using other engine oil weight as rod bolt lubricant. --> Either way, this is why the recommendation is stretch gauge instead of torque measurement. Torque numbers include too many errors: accuracy of wrench, thread differences, friction on threads, lubrication kind, etc...
2. The fasteners that are under stretched, you can undo, clean, put ARP lubricant on, and re-torque to the correct stretch. Stay within ARP's 5% (0.0105") which is better than my cowboy 10% (0.011").
3. The fasteners that are sitting at 0.012" are obviously over the limit of 0.0105 by 15%. I would recommend replacing those with new and follow step 2. It is just not worth it. Even though I know that fasteners recommended stretch is not to 100% yield but a number less than that and you probably have margin, it is just not worth as over time, damage occurs and the outcome is catastrophic.

* Make sure that your stretch gauge is accurate!
** Just because you have torqued something correctly it does not mean that you have the correct stretch because of the variables that impact stretch. So the final truth is stretch.
*** You are not the first to make this error
**** rod bolts maybe the most important thing you will be setting on a high rpm engine, so take your time.

Fabulous

Hello all,
I replaced my bolts with new ARP2000 bolts and this time I documented nearly everything :-)
Torquing went pretty well but two bolts were let's say quite different regarding necessary torque to achieve 0.01inch stretch.
10 of 12 bolts had a final torque between 40 - 44 ft/lbs
2 of 12 bolts needed 55 respectively 59 ft/lbs. I untightend these bolts, applied some more ARP Ultra Fastener and torqued again. But result wasn't different, still high ft/lbs.
Can you give me some recommendation how I should deal with this situation. Can I stay with these bolts?

Thanks in advance and regards
Fabian

Igooz

I don't want to the only person that responds! I hope that others chime in.

Stretch is the true measure of bolt tension and not torque. So if your Stretch gauge is accurate, then you are Golden, go and relax.

When torquing a fastener, some of that torque goes into:
a) friction in threads: lube helps but it does not 100% eliminate it and so you will have unit to unit torque variation
b) friction under the head to the mating surface: lube helps but it does not 100% eliminate it and so you will have unit to unit torque variation
c) actual tension generated in the bolt that you are stretching: There are unit to unit variations in the bolt, but this is typically not much when using a high quality and high grade fastener such as ARP

And finally, there are unit to unit variations between torque wrenches, as well as variations in the same torque wrench torquing fasteners.

And remember that at "proper" stretch, the fastener is typically at 65-75% yield, so there are still margins.

Have a nice day!

Fabulous

I wrote a mail to ARP and they replied that as long as stretch value is in spec, it is ok. They say that difference in needed torque is just friction. So I will stay with it. But to me it is still confusing that friction is varying so much when ultra fastener lube is used…