Consistency of ARP rod bolt length

https://www.enginelabs.com/news/what-i-learned-today-with-jeff-smith-reverse-rod-bolt-stretch-tech/

This article says you can look up the ARP part number for a rod bolt, get the length, and measure it on an already assembled engine to determine if it has the proper stretch/torque.

I have not found the lengths to be sufficiently consistent. Even on one set of rods they vary enuff that I have reset the length gauge from one bolt to the next.

What have you found for length consistency?

I have found this not to be the case on rods that come with ARP bolts. Some are the same, some 2-3-6 thousands off using the same tool in the article.

Possibly a NEW package of un used bolts from ARP might show different. Bit I do not know.

That article does not seem to be correct if they claim all bolts are the same from the start.

The last two engines with ARP 2000 rod bolts (Molnar rods) had around 0.006 variance, so the gauge was different on nearly every bolt.

I feel like the wording is vague, and don't think Jeff Smith was actually suggesting measuring the bolts without loosening and measuring the change. The way I read the article, you take a baseline measurement, loosen the bolt, recheck the length to calculate change and that will tell you if they were torqued correctly or not. Odds are if 1-2 rod bolts are correct, you don't have to check all 16. I pasted the paragraph below for quick reference. He didn't say look up the length as much as look up the original stretch requirements... I actually challenge that approach from a different angle because ARP typically defers required rod bolt stretch to the rod manufacturers.

This technique can also be used to check the veracity of an engine that you may not know the history of. If the rod bolts are from ARP, you can look up the part number and then search for the online instructions on the ARP website to find the original stretch numbers and compare these numbers to what you see on the actual bolts. You may be surprised at what you find, since many engine builders do not use rod bolt stretch when torquing the rod bolts.

In my experience none of the bolts are close. You need to check them individually.
Doug

Exactly my experience as well. Measure individually…..it is definitely important and worth it to do it. Next rebuild, it could prevent a potential bomb.

I've used the stretch method for torquing rod bolts for a lot of years now on ARP and other "quality" bolts. The ARP 8740 bolts and their 2000 and L19 bolts all had some minor length differences in all of them Say from .0003 to .0050
Set the dial indicator at zero for each bolt individually and then stretch them, tighten, torque them and remeasure them for the proper lengths

Recent set of rods with ARP bolts.
1.7590
1.7615
1.7550
1.7571
1.7630
1.7605
1.7628
1.7626
1.7588
1.7567
1.7556
1.7594
1.7592
1.7574
1.7630
1.7588

It would be SO nice if they would precision grind the length. Then we could set the gauge once.

I've been using an angle gauge, then check the length. The angle gauge is pain when the motor is already installed.

I try to write down the torque needed for each bolt to get it to stretch to the middle of recommended lengths, IE.0057 to .0062 shoot for .0059 to .0060.
I do this on the bench with the rods in a rod vice, one bolt at a time
If i was smart I would remove all the bolts and measure the free lengths and then match them up in the rods so both bolts are the same length to start with Instead of doing one at a time starting with no torque and setting the gauge each time on every bolt
I had one Molnar bolt overstretch at 55 Ft. lbs. to start with, all the rest needed 68 Ft lbs. to get anywhere near close the minimum stretch

I've had that happen to me more than once, I didn't feel comfortable with using those bolts so I changed them.

Same here, I record each bolt, before & after, went through 3 "warm-up" cycles before I did the final install.

Having said that, Eagle recommended 75 ft-lbs for 0.0064-0.0068 stretch on my H-beam rods with ARP S2000 bolts...I went up to 85 ft-lbs and that only got me to about 0.0055, take a look at the attachment tracker.

so now with .001 [approximately] less than recommended stretch on the bolts, at 10ftlb more torque than recommended, i wonder what that does to the roundness of the rod diameter ?
also, how does the above affect bearing crush and clearance ?

As far as the roundness of the rod without the bearing in place and torque down to that tightness you should find out
Same thing with the bearings in placed and torqued I have
Most aftermarket replacement bearings will have more oil clearance at the sides where the cap and rod meet than if you make the same measurement aligned with the rod bottom and wrist pins
I've seen from.0010 to .0018 difference at the bearing mating surfaces, that is designed to store oil and lubricate the crank when the engine is running is what Iwas told years ago at one of the Mopar Drag clinics

agreed Cab.
i was wondering what the OP got for a measurement on the big end. [if he measured it as was described by the stretch and torque he mentioned]

Sorry, I'm a little late with the follow-up to your question.

Well, here is another table with the values.

My process actually was to:
1) put the rod in the rod-vise, go through 4 bolt tightening cycles
2) put the rod & bearings in the rod-vise, go through 1 more cycle and measure the bearing ID

All that goes into my table, which gives me an actual bearing clearance, as close to the operating conditions as possible (less heat, stretch, etc.).

Not sure why I had missed the 'HOUSING' size recording for the rods...or it could be that I just tossed that on my whiteboard and missed recording it in my spreadsheet.

All in all I got pretty consistent bearing clearance of 0.002 with a low spot of 0.0019 and a high of 0.0023, but given how tiny that difference is I was happy with the results.

I haven't used torque for so long, I can't remember any measurements. I use an angle gauge, then measure stretch. The big ends check fine. If it takes more torque to achieve proper stretch on any given bolt, it shouldn't affect the big end distortion. Stretch is an indicator of clamping force. If the stretch is within spec, the clamping force should be equal regardless of how much torque it took to achieve it. Variations in the rolling of the threads during manufacturing can affect torque requirements.

I measured the ARP 2000 rod bolt stretch on a set of Scat 7.100 long rods with the Mopar big end today, I had to call Scat to try and get their recommended stretch and torque recommendations on thses bolt( 1.800 under head bolt length, 7/16 bolt diameter. No luck so i called the machine shop that I had pin fit these rods to the wrist pins in the pistons I'm going to use and had them check the rods for roundness and fit on the I.D for the rod bearings, they didn't return the instructions that came with those rods so I called then 2nd. They had to look and called me back and siad they didn't find the original sheet but looked on line at Scat site and came up with 70 Ft. lbs. with ARP lube and no longer than .0060 stretch.
My message is I saw around .0032 rod bolt length variances on these rod bolts with no load, I torque them all to70 Ft. Lbs. and that stretched them between .0041 up to .0053
I'm thinking I will loosen several of them tomorrow and retorque them up to 75 Ft. lbs. and see if that helps getting them closer to .0057 up to .0060

that won't get you up there. Don't chase the stretch number. 75lbs is fine.

Cab : "I measured the ARP 2000 rod bolt stretch on a set of Scat 7.100 long rods with the Mopar big end today, I had to call Scat to try and get their recommended stretch and torque recommendations on thses bolt( 1.800 under head bolt length, 7/16 bolt diameter. No luck so i called the machine shop that I had pin fit these rods to the wrist pins in the pistons I'm going to use and had them check the rods for roundness and fit on the I.D for the rod bearings, they didn't return the instructions that came with those rods so I called then 2nd. They had to look and called me back and siad they didn't find the original sheet but looked on line at Scat site and came up with 70 Ft. lbs. with ARP lube and no longer than .0060 stretch.
My message is I saw around .0032 rod bolt length variances on these rod bolts with no load, I torque them all to70 Ft. Lbs. and that stretched them between .0041 up to .0053
I'm thinking I will loosen several of them tomorrow and retorque them up to 75 Ft. lbs. and see if that helps getting them closer to .0057 up to .0060 "......Cab

i think my old noodle is finally figuring this out. [torque plus stretch] i hope........
he!!, back in my junkyard days, when my partner [R.I.P. Bill. ] and i built engines, we didn't know any more than to mic the crank, measure the inside of the caps with bearings installed, then use plastigauge to double check when the bolts/nuts were tightened. we didn't even calibrate the torque wrenches we were using !
fast forward to today, [50 years ! ] it's a whole new science, so i haft'a learn new tricks, and unlearn my bad habits.
thank you guys for being so patient with such a doofus as i have shown myself to be !