Rod bolt stretch - nuthin' but frustration

Alright...so I thought I'd try to "elevate" my game (LOL, some will agree, some will ridicule, for me it was worth a lesson learned to do so) and decided to take the connecting rod bolt stretch approach this time around.

So here is the thing, I have Eagle H-beam rods which use their ARP 2000 bolts (supposed to be a Eagle spec bolt). I got myself a nice rod bolt stretch gauge, along with a nice 0.0005" Mitutoyo digital dial indicator. Even picked up a connecting rod vise. So far so good.

The free length measured out just fine, no problem, I can spin the bolt while mounted in the gauge and the indicator shows no fluctuation. My dial indicator uses a round shaped tip.

OK, so I toss the rod into my connecting rod vise, tighten and spot-check. The Eagle spec is 75 ft-lbs for a total stretch of 0.0064-8". Now here is the source of frustration: no matter how I hold the gauge with the indicator in it, no matter if I actualy remove the whole rod from the vise and measure that way, the readings on my indicator vary by more than 0.020"...so yeah, it's all over the freaking place!!! It's like I can't find the proper 'center' fit against the rod bolt.

I have a small assortment of indicator tips...you know, round, flat, pointed (cone), etc. So I tried the cone tip thinking that maybe my rounded one was moving around on me too much (which it seems like it was). Still, readings are no better!

No way was I expecting this to be so much of a PITA...it should be much simpler, so what am I missing here? Technique maybe??? Yeah, it's my first time trying this, but holy smokes...one shouldn't need a PhD. to pull this off...right? LOL

Help me out here...what have you guys used as far as setups go, and what do I need to watch out for in order to make my results repeatable?

I had same results as you. Measurements were all over the place. I had Molnar rods with same bolts. I just use Molnar's direction of torque to yield. Torque to 30# then clock bolt 60* if i remember right. Had great results. I think with the Hemi i will just torque the L19's to 95# spec and be done with it.

I got one of the cheap stretch gauges from Summit, and I just lift up on it and twist the gauge. If the needle moves a little, the longest measurement should be the length of the bolt. I find that most rod bolts, about 5 more foot lbs than the spec, puts the stretch right about on the money. With a little practice, I get good results.

I don't rely on the spring pressure of the dial indicator to read rod bolt stretch. Holding the frame of the stretch gauge with the pointy anvil firmly on one end of the bolt, I put the point of the dial indicator on the other end of the bolt and gently press the other end of the dial indicator towards the bolt as I move it around to make sure it's centered and get the lowest reading. So I'm pinching the bolt between the anvil of the stretch gauge and the dial indicator point In my experience that's the best way to get repeatability. Also I don't use 0005" measuring tools for this stuff. I always get the 0001". That makes it way easier, with the tight tolerances on rod bolt stretch. Same thing for my dial board gauge that I use on the big end of the rod, and the cylinder bores, etc. Edit: I guess my memory failed me. I just looked up a picture, and my indicator on this tool is .001"

I took a spring from an ink pen and and small washer I had for rivets as rest on and that put extra tension on the dial indicator plunger so it wasn't all over the place.

You may know this already... Make sure you record all of your torque figures in accordance to the stretch on each bolt... I could save you a ton of time in the future if for some unfortunate reason you would have to break the rods down.
example 79'lbs = .0049 stretch.

I never knew it was this hard or id of never started using the stretch method.

What brand gauge did you buy?

The stretch method is bay far the best as we see even pics on here of folks using tq wrenches from $13 to $350.

ARP 2000 are dummy proof bolts for us and the L19 are idiot proof.

There is some great info on I believe speed talk from some really in the know of how far off you can have the 2000 series and the L19 bolts and they will still work perfectly. The actual specs of what it takes to hurt a arp2000 and then the 19 is pretty substantial. Far more then we will ever put them through. Other things will fail first.

Keep an eye on the entry level eagle arps and they are still a 600hp 7500 rpm bolt that wont fail.

If you get used to the type of bolt you use you learn them. You can tell when a bolt is past its service life when it simply tq-s different then the norm.

Just take a break, look on you tube far a few vids and one day you will be able to set the stretch with your gauge and a breaker bar and a socket.

I dont think my arp gauge years ago even came with instructions. Your rods came with instructions and a area to keep stretch numbers, or they used to.

Straight from arp.

I didnt view this fully.

It would blow you away how easily and quickly I can do it, id explain here but many would give me a funny look, but never ever a bad rod bolt or even a bad rod bearing during inspection.

A decent one.

Its funny he uses two vs just remembering the value and adding or subtracting.

One last tip.... dont monkey around too much running them through the cycles or you will end up buying another set of bolts.

I think my rod bolt stretch gauge and tool are Pro Form, it works great
I bought it from Comp Cams 10 to 15 yrs ago, the dial indicator measures in .0001 increments. I set it at zero on each bolt and then torque the bolts, I sneak up on what the rod makers suggests on torque and find the middle of the stretch, if I can. In other words if they want from .0059 to .0064 I shot for .0061 to .0063. If they suggest 65 Ft. Lbs. I start at 50 or 55 Ft lbs. and go up in 5 lbs. increments
I do see differences in the rod bolt lengths (.00010 to .00030) as well as what torque is needed to get them to stretch to the length I'm shooting for, even on the same rod
I guess it might be faster to remove all the bolts and wash the rust stopper off of them and then premeasure the lengths and then try to match them up on each rod

My rod bolt stretch gauge I have came with a special/modified dial gauge that is high tension/pressure. Are you using one of those?

I started with the indicator gauge method. Gave it up and took the spindle out of a micrometer and ground it to a small radius tip. Perfect, same readings every time. I did the stretch method on one engine about 12 years ago and that engine is still running strong. Have built several engines since then using torque method. Only one gave up the ghost and it was an oiling problem. So decided just torqueing has worked for years. SO why change just because some jackass with a college degree had a wild hair?

I appreciate all the responses you guys.

Yes, I did educate myself as to the tools and various ways of executing this process, but extra materials are always welcome, so "Thank You" Mr PotatoHead!

The bolts have had their free lengths all measured and recorded. Each rod set it flagged as either IN/OUT, meaning with the rod installed on the crank, is the bolt closest to the center of the block (IN), or is it facing OUT. My process so far was to tighted the bolt in: 20-50-60-65-70-75 steps and measure the stretch each time. I figured I would start off with this and as I established the "feel" for how these bolts respond, I would mostly likely just dwindle this down to a 60-65-70-75 stepping afterwards.

I have several dial indicators available, including a 0.0001" as well, which actualy does provide the most stable measurements. My only problem with that one is the fact that the Amazon ad mentioned nothing about it being a 8mm stem and well given that my tools which are all meant for 3/8" I was hesitant to put that one to use. Anyways, last night I tossed it in, it gets locked into place by the gauge set-screw anyways, so no movement is possible and the center of it's stem will be off-center by just a tad. I thought it would be worth it just to see how it compares.

The results are more stable for sure, certainly the precision makes it much easier to pin-point the center of the bolt. It was late, my eyes were tired, I was grumpy and still frustrated, so I wrapped it up. More 'trial and error' today...lol!

Now, most of the time a picture's worth a thousand words, right? So take a peek at a few pics of what I have here.

Ultimately it would seem to me that for this specific measurement a dial indicator with a slightly higher measuring force/pressure is needed. That way the tip stays more firmly planted in either end of the bolt you chose to place the indicator on. I think this is what KD800X is talking about in his post and the reason why Hemi_Joel is relying on a slightly different way of positioning things. I will have to try that.

Thanks again everyone, now off I go back to the "lab" for more experimentation!

Nope, most certainly NOT!

I think that is part of my problem...the tension on the dial indicator plunger is too light and that causes the reading to vary as I attempt to hold the gauge in place to get a reading.

I will try to take the Amazon gauge apart this evening to see if this is something I can change.

The right spring and a small flat washer under the tip should do it.

I just went through a set of rods wanting. .006 to ..0064 . after a couple of rods I found that well lubed 7/16 x 1.60 ARP 2000 bolts needed 87 ft lbs on my old Craftsman beam type torque wrench to be in range, usually .0062. I have click type wrenchs, but that old cheap beam type is as reliable as a hammer.

Dip360 you did adjust the gauge for your length bolt I got to ask? And I like to set it so the gauge is bout 1/2 through its sweep for good tension and then zero it. The arp unit works flawless from the box with the tiny adjustment.

Sure did, great question to ask though.

Here is specifically what I do:
1) measure the free length of each bolt with my micrometer
- the challenge here is that I do not have a point tip on the micrometer and so the length is measured from the top of the head down to the end of the bolt, ideally I would rather match to how the stretch gauge is measuring (the pitfalls of being a DIY guy with a limitted precision toolset)

2) I zero the dial indicator for each bolt when it's not installed in the rod

3) I then torque the bolt and spot-check as per the torque steps I highlighted above
- I tighten both bolts on the rod, but only measure one, which means I repeat this step twice - once for each bolt

4) I then re-check the free length when the bolt it completely removed to see if it got stretched beyond it's capacity

I have my dial indicator about 3/4 through its sweep, leaving just enough to clear the bolt head. I was trying to get the higher spring tension at the top end of the sweep that way.

I have my dial indicator about 3/4 through its sweep, leaving just enough to clear the bolt head. I was trying to get the higher spring tension at the top end of the sweep that way.

What brand gauge did you buy?

My arp thats maybe 18 years old now holds the bolt so well I could toss the whole unit across the shop and not ditch the bolt.

I adjusted a bit too far for this pic.

Here is how I do it. I apply pressure with my thumb. It works fine and is consistent.

I was reading that and found it interesting enough to look into it. More then one way to skin a rod bolt cat.

Yeah, that's what I thought you meant.

I cannot do that as neither one of my higher precision gauges is mechanical, they are both digital.

Having said that, replacing the inner spring to a higher rate one did address the issue I was seeing. The plunger is a lot harder to move now and stays pretty steady. I still ended up tossing a different tip on the other side of the stretch gauge since I found that these bolts didn't have a precisely and smoothly machined recess in the head of the bolt itself. That caused the pointed end to slide around on that irregular surface, enough so that I could see the readings jumping a tad.

Now that brings me to another topic, which is: what is a safe torque to build up to as I attempt to reach the bolt stretch?

These Eagle bolts are meant to go 0.0064-8 at the recommende 75 ft-lbs of torque with the ARP lube. Well, that's nice and dandy but I only see 0.0048 streatch and it only climbs to 0.0051 at 85 ft-lbs. So things are barely moving!

Take a look at the attached chart...start at 65 (half-way through) and wrap around back to the top for the 80 and 85 readings.

I don't know what to make of this, can try to go higher but I'm thinking the recommended 0.0064 is still some ways away.

I used both of my torque wrenches to spot check, digital and the click type, both matched, so I think the torque being applied is true.

I start mine at 65 and when im where you are and im not sure the "book"way but I use my long arm clicker and right after the click I gently pull just a hair like I hit the mark and wanted a bolt snug. Im sure the bolt moves just a few degrees.

You might try that on your current #65 ever so slightly and see how much you add. I shoot for just above the min, spec and ive never go over. I generally can hit it the first or second bump. (not really a bump a gentle pull)

Here is a good read... it says add more tq. at the end of the article. It does not say in what manner. Im sure there is a tq value you could add but I just bang it out. But in the end all that really matters is you get the stretch needed.

https://www.cpgnation.com/how-to-measure-bolt-stretch-for-proper-torque/

Torque them to the recommended value, and forget it.
I have been through this many times. The bolts are never stretched to the recommended length at the recommended torque. You can go to 10% more in ft- lbs on the bolts but don't chase the stretch number you will ruin you bolts.

I torque them, record the stretch. and watch for any abnormalities.

Your numbers are exactly what I would expect to see.

This will confuse you more. About the 2000 series bolts.

https://www.speed-talk.com/forum/viewtopic.php?f=1&t=34381

I will add ive one motor ive never checked stretch, apart each winter with the entry level eagle arp bolts. #63 and never look back.

I really dont know how I got stuck on the stretch thing, sorta like the op, years ago I just wanted to do "better" and that goes back to why I wrote that many think at our power levels we can be semi close and never have a rod bolt issue.

But if the torque value was the best way, why do so many use the stretch?

and if more torque is needed to get the desired stretch, why not just up the torque value, say 10, 15# , or whatever extra ?
wouldn't that basically "average out" the desired stretch ? [provided the correct lube in the correct amount is used]

When I torque them, and I check and record stretch, to see that all the bolts are doing things consistently, as expected. Is that using stretch?
A 7/16 arp 2000 at 85 lbs is around .0055 stretch. If one was different I would check free again.

what would be a good tolerance guideline to follow for stretch ? all being within +/- .000?
trying to learn here.

In my experience if you do that and chase the stretch, you end up putting a lot more pounds on the fastener than the recommended torque.

My gauge reads in 1/2 thous. so I would expect to see between .005 and .006 as an example.

5 & 6 thousandths or do you mean .0005-.0006 [ten thousandths] ?
you wouldn't believe how many engines a buddy and i "built" back in my junkyard ownership days outside on a windy day in the dirt "yard".
they ran reasonably well, considering how ignorant/stupid we were. the older i get, the dumber i realize i truly am.........

5-6 thousandths. My gauge is only graduated in .0005.

Not necessarily, sometimes we overthink things and create problems.

But isn't the recommended torque selected to give you (approximately) the proper stretch? Stretch is all about the clamping force which keeps your rod cap on as the piston reverses at TDC...

I put my 451 together with Eagle rods and ARP bolts... there was a surprisingly large spread in the amount of torque required to reach .0063" stretch. I think it was something like 15 or even 20 ft-lb between the loosest and the tightest (it's been a number of years and I didn't write it down). That was after one cycle for trial assembly.

The torque required to reach proper stretch has a lot to do with the amount of lube used, the machined finish of the washer, nut, threads and rod cap on each fastener

Aha!!! ...and that right there is where I'm stuck today, at least mentally that is. You expect a bolt to stretch by a given amount provided that you apply a certain amount of force that causes the bolt to get elongated. That force being defined and measured as torque.

I haven't had a chance yet to try other rod/bolt combos, which I will tonight. In the meantime though I did get a pretty quick response (a couple actually) from Eagle regarding my follow up questions, basically the matters we have been discussion in this thread here.

My 1st email to Eagle:


Eagle's 1st response:


My 2nd email to Eage:


Eagle's 2nd response:


Man...if I felt frustration initially while attempting to get me a good measure of bolt stretch, that literally pales in comparison to what I'm feeling right now.

Keep in mind I'm an overall newbie in the bigger scheme of things, but I am clearly reading, watching, hearing people out there talk about rod bolt stretch and the bolts having a defined yield value. And here I have a manufacturer that's literally telling me to ignore either one, never combine the two and instead just pick one!!!

My God...so having caughed up the extra cash for a better engineering solution I get to pick the fashion in which I will grenade the motor? (yes, I'm overplaying this, but holy [censored], all of a sudden I miss my stock rods with the ARP wavelock bolts and a simpleton 48 ft-lbs of torque LOL):

1) pick the 75 ft-lbs and never mind that only stretches the bolt to 0.00051 and from an engineering perspective doesn't put it into a state where the bolt will be impart enough clamping force to deal with the dynamics of engine operation???

2) Or on the other hand ignore the measure of torque being applied to a bolt and just bloody yank on the thing until I see the bolt-stretch I aim to see???

....somebody shoot me now!!! LOL

If you go after that stretch number your bolt won't return to it original free length....trust me.
Your numbers look correct . pick a torque and look for an oddball with the gauge, you likley won't find one. and move on. I wouldn't take them to 100ft trying to get the stretch. Iam balancing a set of scat h-beams right now so I just opened the box, they have arp 2000's, the card says torque to 75lbs and in red "do not exceed .006 stretch."

I always check the stretch on the rods I test in a rod vice, if they don't return to zero after loosening they don't get used, I remember having to stretch, tighten, torque, the stock type ARP replacement bolts 3 times before using them. The instruction where to use a certain torque value and then measure the stretch if they didn't return to .000 return then to ARP for replacement
I have had ARP 2000 bolts made for one of the better known Hi Po rod makers over stretch at 55 Ft. Lbs. on a 7/16 bolt
I called ARP and they said to call the rod makers as they had made them to his engineering specs. and he would have to stand behind it, he didn't
His recommendations were torque them to 30 ft. lbs. and then rotate them 60 degrees more I refuse to use that method without a stretch spec which was not furnish with those rods
Hence me starting at 50 Lbs. or less on stretching rod bolts for the first time from then on

The "gotcha" is that the force elongating the bolt is only approximated by torque on the nut. As I mentioned, the relationship between the force and the torque is affected by quite a few variables. But the stretch is directly related to the force by the elastic strength of the bolt material.

I'm getting out of my depth here (I was an EE, not an ME)

My understanding is that torque is easier to measure, so it's more commonly used. Without measuring the stretch, you have no idea exactly how much clamping force is present.

On the other hand, millions of engines have been built with a torque wrench and not a stretch gauge, and they don't seem to blow up any more often... Pick your poison, I guess.

I think the only method that takes all the variables out is Angle Torque.

You take the slack out of the assembly with a low torque setting and then rotate the fastener however many degrees the thread pitch dictates will give you the desired stretch, usually 120 degrees. Friction is the biggest variable that can skew the force applied by a torque wrench and to the readings from a stretch gauge as you have found. Operator error can factor in as well.

X number of degrees of rotation is ALWAYS .xxx" of stretch no matter the friction, the tool or the operator.

Kevin

Unless you have a defective or harder than the other bolts
Been there done that with the ARP 2000 bolts in those race rods I talked about
No one or company makes the exact same after market parts now unless it is the high dollar multi tested space program parts

Defective threads in the nut or bolt would be a problem for sure. But you'd feel that while tightening it.
And if the bolt is "soft" you will have the correct .xxx" of stretch, but below-spec clamping force
But if the bolt is harder, it will take more torque to achieve the same angle rotation (and therefore more clamping force). This wouldn't necessarily be a bad thing as long as it wasn't SO excessive it pulls the end out of round

I guess the conclusion is that angle torquing bolts is a good thing, as long as a minimum torque spec is also met. If not, the fastener is defective...