Rod bolt stretch questions

Hi guys,
Decided to replace my rod bolts , eagle rods , 8740 arp. , unknown history.
Decided to try the stretch method as it makes sense to me. Previously only used torque spec.
I realize my torque wrench is old so felt the stretch method could discount poor wrench calibration.
I am using the method of stretching the bolts with rod in a rod vice and recording torque required to do so .
I am following the arp guide lines and using their supplied lube.
I have read through all of the threads here I could find so I could best understand the process and methods.
I have done one rod and was able to achieve the recommended stretch.

My concern .
In order to achieve the recommended stretch I am 37 ftlbs over the speced 63 ftlbs.
I am going to try a different torque wrench tomorrow to see if the value differs.

Is what I’m finding typical for an amateur with average tools?

Thanks for looking
G

Wow!!! So you are at 100 foot pounds.

I'm no pro BUT I've had ARP 2000 rod bolts that took forever to hit their torque spec - which is totally counter to what you're seeing. Talking to seasoned engine builders its a fairly common thing. If that's what it takes, that's what it takes !!!

LOL cmon man, who wants to see that response!!!!!!!!!
Omg that made me laugh!

Yeah but maybe my t wrench is off by 20llbs.?

That’s why I’m asking , Don’t know what I should be expecting
G

[quote=Stanton]I'm no pro BUT I've had ARP 2000 rod bolts that took forever to hit their torque spec - which is totally counter to what you're seeing.

“Talking to seasoned engine builders its a fairly common thing. If that's what it takes, that's what it takes !!! “

I have read this as well.

Here is one data point. Hopefully some engine builder with lots of data can give you a summary of expected results.
It did take some getting used to using the fixture with the dial indicator on it to get good, repeatable results.
FWIW. These ARP 2000 bolts took 75 ft-lbs instead of the 70 ft-lbs expected to get the stretch.

The torque needed to reach the desire length can and will vary with ARP bolts, especially if they are custom made ARP 2000 for one of the high end rod makers like Molnar
I've seen those bolts over stretch at 53 Ft. Lbs. on one bolt and seen others in the same batch of rods take 83 Ft. lbs. to get in the middle of from .0057 to .0062 bolt stretch
Which ARP bolts are you going to use?
Do one at a time and record the torque needed to get the stretch where you want it and keep it for later on if your planning on looking at the rod bearings so you can retorque them back to exactly what they needed to stretch properly.
Do not use the torque plus so many more degrees of rotation to tighten them

So are you going to have the big end checked after the new rod bolts & different way of tightening the bolts thus changing the amount of clamping force ?

Thanks for responding mr cab . They are 8740 arp

I build a few engines, I am not a high end engine builder. I do use a rod stretch gauge when the rod has the proper bolts. My experience is that it usually takes 5 to 10 lbs more torque to stretch the bolt to specs given. I have never seen something like you describe. I build about 7 to 10 engines a year.

Hmm thanks
G

My experience with using stretch is the torque readings vary greatly. The last time I used torque angle specs provided by Tom Molnar. The stretch numbers were very close. The torque numbers were recorded using a Snap-on electronic wrench. The numbers were much closer together. Sneaking up on stretch creates a lot of friction skewing torque readings. As stated if you don't have a good method to measure each bolt at the start and finish and keep exact records the entire process is useless.
Doug

Ok thanks all. I am going to trash these bolts get two more and just torque them to spec. With a known accurate wrench
G

Tried the gauge on another set of the older bolts. Definitely something wrong, similar results. I ordered a new gauge .
Spoke to Eagle. The gentleman I spoke with felt sure that the rod was not damaged .
Thanks for the knowledge .
I learn something every time I work on this thing.

I still use the torque method(because I dont have a stretch gauge).. I still have my torque wrench calibrated
and its still good to go

My results are similar to yours. ARP makes real hard bolts. And trying to get them to stretch takes way more torque than I want to put on a little rod. Why does everything have to be so complicated? Sometimes I just torque them to the recommended torque realizing that I surely didn't get them to the stretch that it calls for. Bear in mind that everything is going to be fine and it's not going to come apart because you didn't get the proper stretch.

Modern OEM engines solved a lot of the bolt issues by going to torque to yield type bolts. I try to think about bolts like rubber bands, the tighter you tighten them the more they stretch the more the more clamping load they develop. And just like a rubber band you stretch them too much they break. The other concern is the components they hold together can only take so much clamping force. And equal force on parts with multiple bolts is a big issue as well. Torque to yield bolts are designed to stretch past their yield point, which means they will not return to their original length when released, In doing so the load is more constant and you can use a smaller bolt for same clamping loads. I hope everybody knows that a click type torque wrench, should always be rotated to zero when in storage, if you leave a load on the mechanism it will cause problems. I prefer a dial type torque wrench. I use a click type when I can't see a dial, like putting a head on in the car. On the engine stand I always use a dial type, and they are the most accurate.

https://wbtools.com.au/blog/how-to-choose-the-right-torque-wrench

Torque on rod bolts need to be consistent. Do every bolt the same. First torque each rod in a soft face jaws vise. Torque each bolt at least 3 times to torque specs, using the proper lube. Make sure to put lube on the threads but also on the mating faces of the bolt face and the rod surface it mates to. Carefully doing each bolt the same. Then if using stretch method torque each bolt to stretch spec. and record torque reading. Install at same torque and check stretch. Myself I'm an old timer and only use the torque. If you do also, just make sure of using lube on all mating surfaces and torque several times before install. And Good Luck

I have a middle of the road click type that is about 20 years old- where would I get it calibrated or is there a calibration tool I can buy??

Look at the brand name and call that company.. a lot of places have equipment to cal them... I use to
get it done at work then from Snap On.. check the tool trucks for there service

Thanks.
I am a victim of myself. I read or hear of a better way to do things that I have been doing successfully for years and feel compelled to at least try the "better way" . It almost always ends up this way or with no better results. Something in me has really changed with age. When I was 20 30 years old I knew everything and all was well in my mind . Now I seem to doubt and question all I do.

Eagle recommended just checking the bore once new bolts are installed and torqued . Again he felt it would be ok .

8740/2000'S 7/16 rod bolts stretch to .005-.0055 in the 75-85 lb area in my experience. That's where I stop.

Just called Eagle to order two new bolts. When I had him on the phone I started asking questions about measuring the bolt stretch . He stopped me and said they do not do it that way and dont feel its necessary .
Said use their lube , torque both to 25 then, to 63 in one motion .

I am now running into the woods screaming and ripping my hair out!!!!!!

It just never ends.

Had the same problem the ARP lube you are using is not good for rod bolts.
Molnar sends the Extreme pressure lube #3 with their rods because the arp lube cases friction under extreme pressure you are putting them under that's why the torgue is so high
when I use the #3 lube torque and stretch fall within +- 10 lbs to spec
summit part number
https://www.summitracing.com/parts/hrs-99008

I think angle torque is the only way to accurately stretch the bolt without using cumbersome gauges. It removes almost all of the variables, doesn't care about wet threads, dry threads or type of lube. The only witchcraft in it is establishing where "zero" is. X number of degrees from zero is always .00X" of stretch.

As an example, Caterpillar 3406 rod bolts are torqued to 70 ft/lbs + 90 degrees. The mains are 200 ft/lbs + 120 degrees.

Kevin

I have to disagree with this method. I tried it and the it often requires a different amount of torque to get the ideal stretch. Friction is a huge issue. Especially when trying to sneak up on stretch. getting the bolt/nut moving again once the torque is over 70 takes a good deal of effort, well over the number you started with. If the torque gets it to .006" stretch. Then try to get it to .0065", not easy.
Doug

I don't know. It seems there are different methods to do this and they all make sense until someone points out what is wrong with the method.
What doesnt make sense to me is in this day and age of technology a company like ARP doesnt know that if they torque a given bolt to xxlbs that it will stretch between .xxxx and .xxxx ? if they dont know this where are they coming up with the torque spec? And if its so uncertain why even offer a torque spec?
e gads

You're correct it ends up to some where around that number. Torque is a estimate of stretch/friction. That's why the lube makes a HUGE difference. Now combine that with machining process of the threads and you get an estimate. That's why the use of stretch gauges was initiated. To get a better result. I have found a few things about torque in my engine build experience. Multiple short range pulls (20, 40 ,60, 80) are less accurate than a few long pulls (20, 80). After torquing if the fastener is loosened and retourqed in one pull the wrench will generally rotate further the 2nd time. Try it when doing a head gasket. You'll be amazed at the difference.
Doug

It’s kinda funny that guys raced for probably over 50 years using rod bolt torque as the “go to method” of building race engines. Now we are stretching bolts to a given length. Well one guy above said he torque cycles his bolts three times. Well then I’m guessing he installs a bearing and torques it to check rod bearing clearance. If he’s lucky it’s right but if not it’s taken apart to get the right bearings. Then it’s torqued again. This time hopefully it’s dead nuts on so we bolt the engine together. Ohhh damn the Stroker engine rod is hitting the block so we take it apart to clearance the block and assemble it again. All the sudden those new rod bolts have been torqued 3,4,5,6 times. We every bolt has a life and you just used a bunch of them. Just something to sleep on. If you can.

When I first started using ARP rod bolts in stock 440 rods the instruction said to torque, torque them to the torque spec three times with the lube and untighten them three times BEFORE using a stretch gauge
All the ARP rod bolt instructions sheets I have show different stretch lengths for the 7/16 rod bolts depending on the under head bolt lengths
No matter what not all bolts, even made by ARP, are exactly the same and equal on torque needed to stretch them exactly the same

All the aluminum rods I have dealt with were oil only...NO special lubes. On steel rods I always use arp paste with a little oil...

This is fact.

I just got done proving it to my self. Original Molnar ARP2000 bolts that came with the rods go to 85'lbs to get 0062 torque. I ended up having to order two new rod bolts because using the torque angle method I over stretched the fist two I did... (long story) So after I screwed up the bolts, I knew I wasn't going with T/A.....So I ended up going with finding the torque that equaled the stretch tolerance (0060 - 0064) The guy I talked to at Molnar Monday said I was doing it right by doing it this way.

With this being said the new bolts I got in only take 82'lbs to get the bolt to stretch to 0062. If I use the 85'lbs the stretch goes to 0065+ I can only attribute this to the possibility of these new bolts coming out of a different "run".

So what has been working for me is sneaking up on the proper stretch by torquing the bolt incremental until you get with in the published tolerance.
Call the bolt manufacture or rod manufacture who ever the bolts come from and get their opinion. Molnar has been super helpful, spent 20 min on the phone with me talking about bolt tech.

Molnar said you won't over cycle the bolt by doing this. We can tighten and loosen the bolts as much as we need to. It's the pull force when running that stress the bolts.

That's why I'm logging my over all length's of the bolts so I have a base line to go by.

This is my 2 cents .... not sure it's worth it or not.

I go in 5 lbs. torque increments in increasing every ARP rod bolts I test now, one smooth pull to 45 lbs. now and then back it off and see what 50Lbs. measures and go from there, Sneak up on it 5 lb. at a time This method is time consuming but what effort with good results isn't