3.2 ARP Rod Bolts Torque

[mskar]

Hi All!

I was torquing down my rod bolts for my 3.2->3.4 build and was concerned about the stretch procedure. The instructions say that if you are not using the stretch method, then torque them to 40 ft-lbs.

I went through the process, tightening both sides and keeping an eye on the stretch. It went well, but at 40lbs I was still only at 5 (.0005). Using a torque wrench I kept kicking it up by 5, I was at 55ft-lbs and the stretch was pretty even at about 9 (.0009). The process went fine but I'm concerned that my torques are so much higher than the "alternate" recommended torque spec ARP states.

AFAIK, torque wrench is tip-top, its a digital snap-on and I"ve been using it for years. The torque seemed high, so I figured I'd ask if anyone else went through this. My fear is that I just over-torqued these bolts. Can anyone help me out?

Thanks!
Marc

[mskar]

Sounds like 50 ft-lbs or greater is not that unusual. This post:
https://forums.pelicanparts.com/porsche-911-technical-forum/1039455-nervous-about-arp-rod-bolts-used-stretch-gauge.html
Mentions that the poster's ARP installation instructions had 50 ft-lbs as the "non-stretch-method" final torque value. Some older posts mentioned torque values as high as 65 ft-lbs, consensus being: use the stretch value.

Since ARP bolts are reusable, would it make sense to release them all and try again to see if everything is repeatable? Threads and nut faces are well lubed with ARP goo.

[PeteKz]

There's no mechanical reason to not loosen them and retighten to see if you get the same values.

[mikedsilva]

Originally Posted by mskar

Hi All!

I was torquing down my rod bolts for my 3.2->3.4 build and was concerned about the stretch procedure. The instructions say that if you are not using the stretch method, then torque them to 40 ft-lbs.

I went through the process, tightening both sides and keeping an eye on the stretch. It went well, but at 40lbs I was still only at 5 (.0005). Using a torque wrench I kept kicking it up by 5, I was at 55ft-lbs and the stretch was pretty even at about 9 (.0009). The process went fine but I'm concerned that my torques are so much higher than the "alternate" recommended torque spec ARP states.

AFAIK, torque wrench is tip-top, its a digital snap-on and I"ve been using it for years. The torque seemed high, so I figured I'd ask if anyone else went through this. My fear is that I just over-torqued these bolts. Can anyone help me out?

Thanks!
Marc

Yes, a few of us have learned that with arp and carrillo fastners, the stretch method will often (not always) result in a final torque much higher than the specified (in this case) 40 lbft.

Sounds like you're taking a cautious and intelligent approach to your build.

[Dpmulvan]

Had the same problem left them at 50.

[mskar]

Thanks guys. I've had this car off the road since 2015, I got distracted by a couple of needy 928s. I have all of my machine work back and have spent probably 25 hrs on block cleaning since December. I was really hoping to start laying parts into the case this weekend but thankfully I'm catching my mistakes. I have a first edition of Wayne's book (2003?), it says to bring your rods to the machine shop with the old bolts. Current wisdom (as well as the ARP instructions) says to get your rods conditioned with the bolts at final torque. This makes perfect sense but I didn't realize these bolts could be retorqued. Thank God for this forum, seems like there's a hundred different ways to screw up your rebuild.

[stownsen914]

I had a similar experience using ARP bolts in Carrillo rods. The published torque number, while different from the bolts you are using, was substantially below the torque it took to get to the stretch number (.0065" in my case). Took an extra 20 ft-lbs. Wound up talking to Carrillo and ARP to make sure I wasn't missing something.

I saw in your other thread that you're sending your rods back to the machine shop. Was going to say, for ARP bolts, you need to check that the rods don't go out of round when torqued to the higher number / stretch per ARP instructions. This may be what you have in mind, but wanted to mention. In my case, I was able to verify with a bore gauge that there was no out of roundness with my Carrillos when torqued to the higher number.

By the way, you mention that you were looking at .0005-0009" stretch. I think you mean .005-009" ? That would be more in line with typical rod bolt stretch values.

[MoreGAS]

Hello Mskar
What you are trying to achieve is roughly a preload value of 70% of the bolt's yield strength, which is difficult to achieve reliably w a Tqe wench for a variety of reasons; your Tqe wrench's health, the lubricity of the nut in the threads(use only the assembly lube supplied) , the friction under the nut, cleanliness, technique (ie-sailing passed where the wrench clicks )...With all this in mind it is easy to see why Torquing is not very accurate and it is often reported that you may only get within 25% of your targeted value.


Your ARP fastener kit instruction set is here
https://arp-bolts.com/kits/instructions.php?RecordID=1200

and from memory they were never at the huge range as you call out .005-.009" but I sense these have been revised recently, which seems to be happening with our common Hi Perf. rod bolts lately( w Carrillo also) lately. They all are looking for greater strength in this joint. I recall the old values were more like .009-.0105 " . I cannot recall ever seeing an ARP bolt in a Carrillo rod, at least not the last 20 years as it was always SPS Carr bolts, PS, or WMC bolts.
Stown914 make sure you don't have some Chinese knock offs!

This is why a stretch gauge is the far (and only) superior way to approach this task for the most critical fastener in the engine, really the Achilles heal of these engines. They are available for not alot of dough, maybe 125-150 USD.

Remember to check your big end bores once you put the upgraded Bolts in tightened to the correct stretch, they can distort, and if they do you will need to have them resized. This is not uncommon now that Carrillo no longer uses SPS Carr bolts, but switched to a different Pro Stock bolts, with a much greater amount of torqe-ing required to get to the stretch specified.

We have seen this case where the stretch will not come-in at the upper limit that is often given for a not to exceed value Your spec sheet above does not provide one so I would contact ARP and ask them. We typically run in to this w Hi end bolts servicing Titanium rods, and sometimes on SPS Carr bolts or Pro stock bolts. IN this case we back them off and Torque again to upper limit given and stop there. We haven't experienced these 9mm ARP bolts having this issue as they are so long, and w the tapered waist they stretch like taffy (compared to others) but would still be good to know what ARP says is the limit. If you logged their individual length new as they note, you would know if you over did it by seeing one retain more than .001" stretch, basically it has yielded. New their lengths can vary as much as .006-.007 " which can be a little off-putting. So you must have recorded each of them new(based on position) to assess.

This also reminds me of a poster here sharing that you don't need the Hi end bolts like SPS Carr or PS bolt for the street, the basic upgraded bolts will be fine at 7200 ish RPM. What we need to consider is that once in a great while where you mean to stick it in 3rd but you accidentally stuff it in 1st, and now you hit 9500-10K instead of 7200 limit in your mind. In this dept. one cannot overdue the technique or the best material choices .

Good Luck

Kevin
GAS Motorsport

[stownsen914]

Thanks Kevin. I bought from Summit Racing to (hopefully) eliminate the chance of counterfeit parts. The ARP bolts are a product they make as a replacement for the Carrillo SPS Carr bolts.

[mskar]

Thanks for the feedback guys. I pulled the rods back off the crank yesterday, they returned to their pre-stretched sizes. I retorqued them onto the rods so that I can bring them to the machine shop, this time it took only 40-45 ft-lbs to get the correct stretch value (which is .0100-.0105 if I got the decimal right this time!). I very much appreciate the help!