ARP2000 rod bolts

[FabianK]

Hello all,
I have some questions regarding the ARP2000 bolts:
1) I installed the bolts with a stretch gauge and torqued them to the recommended stretch of 0,01inch. Unfortunately I found out that the gauge has some accurancy though handling. I made a statistic and came to the result, that my real stretch of the bolts is somewhere between 0.009 - 0.012inch. Tolerance is 0.01-0.0105inch.
I'm questioning myself whether I can stay with it or not. Does somebody know how close 0.01inch is to the tensile strength? I hope there is still some safety, especially when you torque without a stretch gauge to the specified 40ft/lbs the tolerance will be much more then 0.01-0.0105inch, or am I wrong?

2) When I compare the bolts to the original bolts I'm questioning myself if there really such a big difference. Why do I think so. Torquespec of the original bolts are 15ft/lbs + 90degree. The thread has a pitch of 1mm = 0.04inch. So the original rod bolt will have a stretch value also around 0.01inch like the ARP2000 bolt. As both materials have a similar e modulus there can not be such a big difference in clamp load or let's say just a little difference if original rod bolt has a smaller elastic range. Or do I have a mistake in my calculation.

Appreciate your help!
Regards
Fabian

[Flat6pac]

The later info on the OE rod bolts is a second 90 degrees.
It has to do with the spec on the bolt top, newer ones torque twice, early ones torque once.
Bruce

[Tippy]

I believe there is a chart showing the yield stretch dimension. I bet you are fine, but I'd confirm.

[FabianK]

unfortunately I cannot find a yield stretch diagramm. And ARP is not really a help. They just say, if there is a chance that stretch is More then 0.0105 I should replace. No comment if there is some safety or not. Which I don‘t understand because as I wrote torquing with just a torque wrench will result in higher tolerances. Or will 40 ft/lbs lead to a far lower stretch than 0.0105inch?

['78 SC]

Did you record the length of each bolt when new with no tension? Do they all still measure the same? That would be the first check on whether the bolts have been overtightened (beyond the elastic limit).

[FabianK]

Unfortunetly not. I know that was a Kind of stupid…I ordered already new ones.

[FabianK]

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

[AVI_8]

Fabian, it was my understanding that these bolts can be torqued more than once anyway so long as they are measured before stretching and they go back to their original size when removed.

For an example when re-sizing rods the ARP bolts are used during this process and then re-used during engine assembly.

I know its too late now as you’ve replaced the bolts but if you haven’t thrown the old ones away it would be interesting for you to measure them and see if any of them had stretched beyond their original size which would indicate if a particular bolt had been stretched beyond its yield strength. If not your original bolts are probably still usable.

[FabianK]

Hello Avi,
unfortunately I did not measure my first bolts so I have no chance to evaluate if they have original size. That is why I bought new ones.

Regarding my torque values. Have you made similar expiriences?

[AVI_8]

I haven’t started my engine rebuild yet, that’ll be later this year, I’ve rebuilt several engines in the past (not Porsche) and only ever used a torque wrench but yes from many of the engine rebuild threads I’ve read on here it’s not unusual to have varying torque settings on different bolts in order to get the required stretch value.

[ahh911]

I don't know how relevant to arp bolts, but when I intentionally overtorqued the original rod bolts in my 81 sc (around 75Nm I believe) in a test setup, they stretched, and everytime thereafter even with lesser torque they stretched again. I would not rely on this statement as science, but it seemed to work that way (i'd have to double check my notes). Basically below the original yeild point but much greater than the spec'd 55Nm they would not yield, once above the yield point and stretched, they would stretch between 55Nm and the original yield point of around 75 Nm and stretch more and more from there on. Check with arp about this statement, you should call them before you put the replacements in as you may get a refund.

I see you've installed the new ones, why not test the above statement with the ARP bolts? The hardest part is creating a good test fixture that has good repeatability. I would like to know the result of the test, maybe it's common knowledge already to those immersed in the field.
Phil

[faapgar]

I have used many sets of these over the years.In the 70,s we were buying 917 Titanium rod bolts for the 2.4-2.7 type engine.ARP bolts have always been very consistent as far as stretch.The 2 that torqued at 55-59 lbs.I would be suspicious of.The 917 bolts could be used again and again.The key was during a freshening when rod bearings were changed after 40 hours to keep a written log of the length.If they did not change just reuse with new nuts.If you use the Blue Pac of ARP lube your torque will be consistent.SPS Carr hardware is also very good.Fred

[FabianK]

Hello,
I untorqued both bolts with high ft/lbs and they came back to original length, so no permanent stretch. But when I retorque them both bolts need same high torque to archieve the desired stretch of 0.01inch. I do not think that material is varying much so the high difference will ne either high friction in the threads or under the nut.
Fabian

[BURN-BROS]

My experience with the ARP 10mm bolts is around 50lbs to get my desired stretch. This is on multiple sets spanning 10 years.

[FabianK]

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…

[BURN-BROS]

Torque is the least reliable way to measure fastener preload. I rely on stretch and verify I am close to the torque spec or higher. I have kicked out a few that went to stretch well before the torque requirements just as a precaution.

[LJ851]

If it’s not the bolt and it is friction related to the rod, you could verify this by removing another bolt that stretched with the lower torque value and install it in place of the higher torque value bolt.

[FabianK]

Thanks all for your comments.
I read somewhere that friction consumes 90% of friction, so there cannot be another reason that torque is nearly 50% higher, than on other bolts.
I think the reason is the nut and its higher friction to the rod or the thread itself. When I torqued the first bolts, I had the same phenomenon, but on another rod.

[stownsen914]

It's generally accepted that stretch is better than torque to achieve the desired clamping force. But if you need 50% more torque to achieve desired stretch on a bolt, it would lead me to dig in to ask why. I'd ask questions like:
Did I make a mistake?
Is there a flaw in the bolt or nut?
Is my torque wrench broken or miscalibrated?

['78 SC]

Originally Posted by ahh911

I don't know how relevant to arp bolts, but when I intentionally overtorqued the original rod bolts in my 81 sc (around 75Nm I believe) in a test setup, they stretched, and everytime thereafter even with lesser torque they stretched again.
Phil

I'm not a mechanical or materials engineer, but I think that's pretty much the definition of stretching a bolt beyond it's elastic limit.


As far as needing to use different torques to get the same stretch, I went through the process of measuring the torque needed to get proper stretch on a set of ARP bolts a few years ago. Highest torque was 75 Nm (53 ft-lb), lowest was 64 Nm (45). Most (9 bolts) were +/- 2.5 Nm (1.8). I used the recommended ARP lubricant and loosened and re-torqued each bolt several times to get the measurements.

My torque wrench is not certified, so I can't vouch for absolute numbers. In this case I just needed repeatability, since I was installing a set of rods without splitting the case and I needed to know the torque needed to bring each bolt to correct stretch.