I am torquing down rod bolts today using a GRP stretch gauge.

I have Scat I beams with ARP # 8740 7/16" x 1.400 cap screws rod bolts. The torque spec is 64 ft. lbs, not to exceed .0046" stretch.

Torquing to the 64 lbs, I am getting .0035, .0040 and a few that are right at .0045.

If the stretch reading was on the low end, I loosened the bolt and re did it but it usually stayed the same or only added .0005".

Am I good?

I'd be worried that you don't have enough stretch on the two "low" ones regardless of the fastener torque. Could there be a burr on the mating surfaces, or lack of lubricant?

Plenty of lube, used the ARP stuff that came in the box. I smeared it on pretty good.

Do you know for sure whether there is a recommended range or is there a specific value I am looking for? It does say NOT to exceed .0045" but I guess the question is do you actually NEED more than .0035"?

At the very least, the bolts are torqued to the recommended setting...

The stretch should override the torque, its the real measure of how much the bolt is holding, torque is the estimate of the resistance needed to get to that point.

Torque can be affected by the lube used, torque wrench, extension used, etc..

Make sure the stretch is correct is the priority.

OK, I understand the concept of stretch and how it overrides the torque spec but what is the proper amount of stretch? The box says .0046" is the stretch limit and I'm fairly close to that with most of the bolts, like .0040" or so.There's only 3-4 that are at .00035"

If I zero the dial indicator when the bolt is at rest then torque it to 64 ft. lbs., (as a starting point) I get anywhere between .0035" and .0045" stretch. Is this enough? If not, what am I looking for? This is all I am really asking here. Is there a percentage of the yield or something like that?

I only stated that the bolts were torqued to the proper spec because at least I know there is some stretch at that torque value. Again, I am not sure if it is enough or not. ARP gives the torque spec so at some level it may be sufficient. I'm not willing to roll the dice though which is why I am asking here.

Seems like there is a pretty big difference in torque between .0035" -.0046" stretch?

Write down the number and position(# 3 rod, inner bolt, #7 outer bolt and so on) of the stronger(shorter with the same torque)and try adding 5 lbs at a time until you get those bolts stretch to the middle of the range Keep those records and use them when retorquing all of the rod bolts WITH THE SAME Torque Wrench I hate it when you get a set of rods that have bolts from two different batches of heat treated bolts IHTHs

Cab, I had some of the bolts up to 80 ft lbs with no appreciable change in stretch. But I just realized I may have been getting to the final torque spec incorrectly. I'm thinking you have to undo the bolt every time you need more torque then do it in one sweep? The way I was doing it was just adding 5 lbs, then another and nothing was happening. I will undo some of the lower spec bolts and see if doing it that way helps. I suspect it will. Maybe I might end up re-doing them all if that's the case...

But again, is .0040" where I want to be regardless of the torque spec?

If the stretch spec. calls for .0039 to .0045 I would shoot for .0042 to .0043 on the stronger bolts Always loosen the bolts before adding additional torque and retorqueing

There is no specific stretch spec. though, only a limit. Hence my confusion.

I agree. The stretch method is much more accurate than torque ft lbs. Steel stretches just like a rubber band, only a lot less and when it goes past a certain point it is hurt. The other thing is, at about the number they want you to stretch it to it is at about 75 percent of that max value before the metal is hurt and that is where it will work best and have the longest life, if I understand it correctly. I have also read that a bolt stretched to half the value it needs will only support half the load, probably because it can stretch more easily and will start to stretch at some point after that smaller load is passed.

First off you don't use a torque wrench when your using the bolt stretch method. Set the gauge on the bolt at rest and with a long box end wrench start tightening the bolt until you reach .0045" bolt stretch.
You have to do each bolt separate.
That's it.

Go to K1 Technologies catalog pages 22-23 it is explained there.

This is the way I do it also, it's very time consuming and a pain to do but at least you know that every bolt is where you want it as far as stretch goes.

A lot of us use the torque wrench as a guide to how much further to go. I want to stretch the bolt to spec, and a box end wrench doesn't give you any reference point to work off.

That's what I was saying, I use the torque spec as a starting point. 64 ft lbs. is a first check. If it's too light then OK, undo the bolt and swing it up to 70 ft lbs and see where its at and so on. I stated above that I was adding torque incorrectly so that was probably my main issue right there and why I was getting the lower stretch readings.

Using a box wrench is difficult to get it to where you want it, I tried. You need a really long one with a 12 point wrench pad which I don't actually have.

Again, my main question here is whether there a minimum amount of stretch that you want to achieve beyond the zero point/free length. If there is, you would think it would be known and clearly stated like a torque spec.

However, if you go by the 75% idea then .0035" should be fine since 75% of .0046" is 0.00345".

Thanks for all the input.

I guess I don't understand what you are saying?
The stretch gauge stays on the bolt until you are done.
What do you mean no reference?
I'm telling you don't use a torque wrench for the bolt stretch method. What if you go to 70lbs/ft and the bolt stretches to .0047" the bolt is now junk because you went to far.
This is a subject that needs to be better understood by guys that don't understand the bolt strech method.

Just use the torque factor and be done with it. Don't try to use one to get the other, you will end up having a failure.

I have a better understanding of this now. It is true, you don't need a torque wrench, it actually has no bearing on the procedure. Thanks for pointing this out, much appreciated.

I called and talked with ARP today about this. The guy on the phone suggested tightening the bolts using a crow foot wrench on a breaker bar with the gauge installed so you can watch it. So right there there is clearly no need for a torque wrench. You'd be there all day loosening and tightening trying to use a specific torque value as a reference. The proper way to do it is to loosen it and come up on the 'torque' swiftly. He said if you do it slowly you end up twisting the bolt.

The guy on the phone said I was basically on the right track but I just need to keep going on the lower ones. As far as a specific stretch amount, he said he'd want to see somewhere between .0040" and the .0046" limit.

It is a little confusing that Scat publishes the torque spec and then gives a stretch limit, but I guess they figure people still don't/won't use the stretch method and would rather rely on a torque spec.

So unfortunately I don't have a 7/16 12pt crow foot. Went to Sears this afternoon, couldn't find one. Might try to use a combo wrench with a cheater pipe if I can figure out how to make it work.

Anyway, time to put the torque wrench away and do this properly.

DO NOT go less than .0003 or .0004 than the max stretch indicated for a given bolt. If it says .0046, you better be at .0043 or more. My rod bolts call for .0067 to .0071 and I shoot for .0069.
When you get to the maximum stretch figure, like .0071 in my case, that is the point that the bolt will hold the biggest load. Anything less takes away the holding capacity, proportional to the amount you are short. If your bolt calls for .0045 and you put it at .0030, you just reduced the clamping force by 1/3rd, and it is that much easier for the rod to distort.