ARP rod bolts installed in S50

[UweM3]

I am a little bit puzzled. Installed some ARP rod bolts today and reading the instructions ARP recommends to use a stretch gauge. So would I, but reading the recommended value of .0068 of strech I am a little bit concerned because the alternative method they give is to use a torque wrench and tighten and loosen the bolts 3 times to 50lbs.
50lbs preload is for sure not going to stretch the bolt by 0.0068
What I am missing here?? How have you done it?

[martinpallot]

We did the latter method on my mates e36 rally car as we didnt have a stretch guage. Has been running fine ever since, so from personal experience it seems to have been sufficent. I doubt ARP would risk the bad press and put something they are not sure of in the instructions. hth

[reggid]

I am a little bit puzzled. Installed some ARP rod bolts today and reading the instructions ARP recommends to use a stretch gauge. So would I, but reading the recommended value of .0068 of strech I am a little bit concerned because the alternative method they give is to use a torque wrench and tighten and loosen the bolts 3 times to 50lbs.
50lbs preload is for sure not going to stretch the bolt by 0.0068
What I am missing here?? How have you done it?

50lb-ft torque is not exactly tiny........

[UweM3]

We did the latter method on my mates e36 rally car as we didnt have a stretch guage. Has been running fine ever since, so from personal experience it seems to have been sufficent. I doubt ARP would risk the bad press and put something they are not sure of in the instructions. hth

Didn't mean the instructions are not right, just felt that the amount of stretch achieved seemed a bit high for 50lbs.
I have confirmation from a chap in the US that the bolts did stretch indeed to 0.006 with 50lbs.

[GeoffBob]

Uwe,

I think maybe you are making the mistake of thinking that 50lb-ft of torque puts 50lb's of load on the bolt? That certainly isn't the case.

Your rod bolts probably look something like this, right?



Note the narrowed region below the head of the bolt. This is where the bolt stretches. Now, I'm guessing that your rods use M10 x 1mm metric bolts, where the "neck" is about 20mm long and has a 9mm diameter?

Now (ignoring friction on the thread), you can calculate the axial load on a bolt using the following (non PhD level ) equation:



where:
F is the axial force on the bolt (in Newtons)
T is the torque applied to the bolt (in Newton-metres), and
p is the bolt pitch (in metres).

Now, your ARP bolts should be torqued to 47lb.ft, which is equivalent to 65Nm (metric). Thus, for a bolt with 1mm pitch, the axial force on the bolt is calculated to be 408.4 kN (that's about 40 metric tons of load on that teeny weeny bolt BTW).

Unfortunately, even with a good quality molybdenum based grease you can expect 80% of this figure to be applied to the friction on the thread, and only the remaining 20% to be stretching the shank.

The amount of strecth that this causes can be calculated using the following equation:



where:
d is the amount of stretch (in metres)
F is as calculated in the first equation (in Newtons),
l is the length of the narrowed bolt shank (in metres),
r is the radius of the narrowed shank (in metres)
and E is the modulus of elasticity (Youngs Modulus) of steel (in Pa)

The factor of 0.2 comes about as a result of the friction on the thread (as described above).

For an M10 rod bolt the narrowed shank has a diameter of about 9mm, thus r=0.0045m. For ARP rod bolts, typically, l=0.020m.

For steel, regardless of heat treatment, carbon content or alloying, E=207 GPa (that's 207,000,000,000 Pa).

Putting these values in the the second equation, d=0.000124m, or 0.124mm. Converting to inches, d=0.0049", which isn't far off the specified stretch value of 0.0056" to 0.0060".

Not bad for for a crude estimate don't you think?

I'd say the ARP specified bolt torque is exactly what's required to give the specified amount stretch.

EDIT: And BTW, don't ever ever ever re-use ARP rod-bolts after they have been stretched!

[DanThe]

I was just about to say that

[UweM3]

Uwe,

I think maybe you are making the mistake of thinking that 50lb-ft of torque puts 50lb's of load on the bolt? That certainly isn't the case.

I have never said or thought anything like this. The question asked was if 50lbs of torque is applied will this stretch the bolt 0.006 and obviously it does. I just wanted to double check this.
ARP bolts are supplied with a special grease to make sure the friction is dealt with.
Also taken from the ARP instrucions:
If the torque method is used tighten and loosen the bolts THREE TIMES.
So much for not re-using the strechtbolts. I would re-use a stretch bolt is the unloaded length hasn't changed. I have measured each single bolt before install.

BTW this is how bearing on No6 is is looking! Crank journal and all other bearings are 100%

[GeoffBob]

Well pardon me if I understood your statement:

50lbs preload is for sure not going to stretch the bolt by 0.0068

to mean that 50lbs preload is for sure not going to stretch the bolt by 0.0068.

Uwe, the bolt doesn't have 50lbs of load on it

And no, the "specially formulated Moly base assembly lubricant" doesn't take care of the friction. There has to be friction on the bolt thread to stop it from unwinding itself the instant you take the wrench off the bolt head. Otherwise it would be like letting go of a spring - kapoing. The supplied lubricant simply ensures that you get (approximately) the right amount of stretch vs friction, which is also why you undertake the exercise 3 times.

Oh, and BTW, YOU'RE WELCOME. I work with ARP's regularly, always a pleasure to share my knowledge with someone who appreciates it.

[UweM3]

Well pardon me if I understood your statement:

50lbs preload is for sure not going to stretch the bolt by 0.0068

to mean that 50lbs preload is for sure not going to stretch the bolt by 0.0068.

Uwe, the bolt doesn't have 50lbs of load on it

And no, the "specially formulated Moly base assembly lubricant" doesn't take care of the friction. There has to be friction on the bolt thread to stop it from unwinding itself the instant you take the wrench off the bolt head. Otherwise it would be like letting go of a spring - kapoing. The supplied lubricant simply ensures that you get (approximately) the right amount of stretch vs friction, which is also why you undertake the exercise 3 times.

Oh, and BTW, YOU'RE WELCOME. I work with ARP's regularly, always a pleasure to share my knowledge with someone who appreciates it.

are having the split hairs converstion again?

OK I rephrase, 50lbs TORQUE on the bolt. We had this discussion before GeoffBob, unfortunate for you not everybody has a PhD here, especially not me. So you will have to deal with us dummies, even if we get the terms slightly wrong sometimes.

Do you know what, somebody on S14 answered my question in ONE sentence (and the text of my question is 1:1 copy from here), why do you always need to impress with a mile long, formular riddled answer??

[Aubs]

[GeoffBob]

why do you always need to impress with a mile long, formular riddled answer??

Because you asked and I thought I was being helpful.

I've got news for you Uwe, what I posted is pretty basic stuff. I went to great lengths to answer your question in a way that I thought you could understand and you might find useful in future. I'm not trying to impress anyone and I am sorry that you see my posts as such. I always back-up my replies to technical questions with sufficient level of information in order to assist the reader better understand the topic under discussion. I had hoped that the information I provided would be of some help to you. Other members on this forum have thanked me for the effort I put into explaining things clearly. I am sorry that you feel differently.

[Jhonno]

why do you always need to impress with a mile long, formular riddled answer??

Because you asked and I thought I was being helpful.

I've got news for you Uwe, what I posted is pretty basic stuff. I went to great lengths to answer your question in a way that I thought you could understand and you might find useful in future. I'm not trying to impress anyone

It might not be complicated in the grand scheme of things but it is still degree level mechanics.. If you didnt study it, then it is going to be complicated.. By reeling it off and then stating it is simple is showing off in my opinion..

Uwe.. I just torqued mine up 3 times, and they've been fine.. Not the most scientific method sadly, but i just followed the instructions and it appears to have worked

[GeoffBob]

It might not be complicated in the grand scheme of things but it is still degree level mechanics.. If you didnt study it, then it is going to be complicated.. By reeling it off and then stating it is simple is showing off in my opinion..

Jhonno, I posted what I did with the honest intention of being helpful. How either of you can respond to what essentially amounts to just information with a personal attack is beyond me. If the information I presented is beyond your scope, or you are at a different place on the learning curve then feel free to ignore it, ask a question, whatever. But this level of personalisation is uncalled for.

[mt1104]

It might not be complicated in the grand scheme of things but it is still degree level mechanics.. If you didnt study it, then it is going to be complicated.. By reeling it off and then stating it is simple is showing off in my opinion..

Jhonno, I posted what I did with the honest intention of being helpful. How either of you can respond to what essentially amounts to just information with a personal attack is beyond me. If the information I presented is beyond your scope, or you are at a different place on the learning curve then feel free to ignore it, ask a question, whatever. But this level of personalisation is uncalled for.

+1, its just information

[DanThe]

You obviously cant please everyone. I wonder what would have happened if a simple yes/no answer had been posted

Maybe you should set a max word count for answers to your questions uwe

[UweM3]

You obviously cant please everyone. I wonder what would have happened if a simple yes/no answer had been posted

Maybe you should set a max word count for answers to your questions uwe

maybe I am a little bit over sensitive, but I am just fed up that everytime I don't get an engineering term right I get a "oh you didn't know that" and "that's just common knowledge" answer.
Let's be honest, could you have worked out the strechted length like GeoffBob did? I can't. And to be honest I don't need/want to know it anyway. I trust ARP products, why do you think I bought them? I just needed a little bit of confirmation that I understood the instructions right. I am just a simple welder.....

If I would have a bolt in a different application and no proper instructions I would ask for more details if I am in doubt. Or I would buy a book and read it to work it out.

[GeoffBob]

Uwe, sounds like you are more concerned with the way I answerd your question than the actual answer I posted?

I am sorry I bothered you with a little more technical detail than you wanted. I can assure you it was posted with the best of intentions and I had hoped it would make your work with stretch bolts easier in future. I made a specific effort to present my explanation as clearly and simply as possible. I can also assure you that any corrections to your terminolgy are for the sake of accuracy and certainly not intended to diminish your efforts.

I still maintain that your response to my post was out of line. I shan't make the effort on you in future, and it did take quite an effort to type up those equations and draw that stretch-bolt for you. Maybe someone else reading this thread can find some use in that information, even if you choose not to.

Oh, and BTW, I could tell you whats going on inside your No. 6 bearing cap, but why should I bother when you might not like the answer you get.

[Jhonno]

It might not be complicated in the grand scheme of things but it is still degree level mechanics.. If you didnt study it, then it is going to be complicated.. By reeling it off and then stating it is simple is showing off in my opinion..

Jhonno, I posted what I did with the honest intention of being helpful. How either of you can respond to what essentially amounts to just information with a personal attack is beyond me. If the information I presented is beyond your scope, or you are at a different place on the learning curve then feel free to ignore it, ask a question, whatever. But this level of personalisation is uncalled for.

You missed my point, it was nothing to do with the actual information, I have no issue with it and it is a good read for those that choose to read it, it is just the delivery at times is not always as good.. It wasn't meant as a 'personal attack'

[march109]

why do you always need to impress with a mile long, formular riddled answer??

Because you asked and I thought I was being helpful.

I've got news for you Uwe, what I posted is pretty basic stuff. I went to great lengths to answer your question in a way that I thought you could understand and you might find useful in future. I'm not trying to impress anyone

It might not be complicated in the grand scheme of things but it is still degree level mechanics.

Disagree there, I saw that formulae in A-level physics, though that was a decade ago now.

I always like to see 'how' an answer has been arrived at, opinions are like arse holes but fact based on math can only be wrong if there is an error in the calculation. 2 + 2 will always equal 4.

I at least learnt how to apply some math I knew to a situation I hadn't thought of before. Hopefully I can find more use for some of the rest of the bollocks I know.

[Jhonno]

Because you asked and I thought I was being helpful.

I've got news for you Uwe, what I posted is pretty basic stuff. I went to great lengths to answer your question in a way that I thought you could understand and you might find useful in future. I'm not trying to impress anyone

It might not be complicated in the grand scheme of things but it is still degree level mechanics.

Disagree there, I saw that formulae in A-level physics, though that was a decade ago now.

I always like to see 'how' an answer has been arrived at, opinions are like arse holes but fact based on math can only be wrong if there is an error in the calculation. 2 + 2 will always equal 4.

I at least learnt how to apply some math I knew to a situation I hadn't thought of before. Hopefully I can find more use for some of the rest of the bollocks I know.

Possibly an example of how education is getting easier then as i didnt.. Though to be fair I could have paid more attention

I agree.. Though you havent seen me with a calculator. 2+2 can equal whatever i want to it

There was no issue with going the extra mile.. You can read it or skip to the last page to find out what happens.

[UweM3]

Oh, and BTW, I could tell you whats going on inside your No. 6 bearing cap, but why should I bother when you might not like the answer you get.

why doesn't your answer surprise me.......

I guess it's just to my lack of humor (because I am german) as you already had sussed out earlier.

[GeoffBob]

Because you asked and I thought I was being helpful.

I've got news for you Uwe, what I posted is pretty basic stuff. I went to great lengths to answer your question in a way that I thought you could understand and you might find useful in future. I'm not trying to impress anyone

It might not be complicated in the grand scheme of things but it is still degree level mechanics.

Disagree there, I saw that formulae in A-level physics, though that was a decade ago now.

I always like to see 'how' an answer has been arrived at, opinions are like arse holes but fact based on math can only be wrong if there is an error in the calculation. 2 + 2 will always equal 4.

I at least learnt how to apply some math I knew to a situation I hadn't thought of before. Hopefully I can find more use for some of the rest of the bollocks I know.

Thanks March 109, I appreciate your comment.

The way I see it is, if it's useful information to someone, then great, I am glad to help if I can. If not, then as Jhonno said, anyone can just skip to the end and arrive at the answer.

Uwe, I'll say this only one more time: I am sorry I bothered you with a little more technical detail than you wanted. I can assure you it was posted with the best of intentions and I had hoped it would make your work with stretch bolts easier in future. I made a specific effort to present my explanation as clearly and simply as possible. I can also assure you that any corrections to your terminolgy are for the sake of accuracy and certainly not intended to diminish your efforts. Your response to my post was, however, out of line.

[UweM3]

Uwe, I'll say this only one more time: I am sorry I bothered you with a little more technical detail than you wanted. I can assure you it was posted with the best of intentions and I had hoped it would make your work with stretch bolts easier in future. I made a specific effort to present my explanation as clearly and simply as possible. I can also assure you that any corrections to your terminolgy are for the sake of accuracy and certainly not intended to diminish your efforts. Your response to my post was, however, out of line.

OK maybe I had a bad hairday, but I do feel hunted by you whenever I get something a little bit wrong in terms.
I may not know all the nitty gritty details about engineering/math etc but I do have a basic understanding of mechanical components gained over many years through trial and error. It's not that I have never had a strechtbolt in my hands, I was just a little bit courios.

Call me sensitive but I do class your writing style as a little bit partonising/lecturing. Maybe you don't realise this, but remember I am not the only one pointing it out to you.

I do apologise for not honouring your good intentions, but I do not apologise for voicing my opinion.

[Supafly]

Thank you for the information GeoffBob. I've definately learnt something new today
and bookmarked it becauseI know I'll forget by tomorrow!

[Omi]

Ah, you're German, Uwe! - I was curious about the ridiculous amount of over-engineering going on with your S50 conversion...

[UweM3]

Ah, you're German, Uwe! - I was curious about the ridiculous amount of over-engineering going on with your S50 conversion...

Oiii! What do you mean by over engineering? Form follows function. Would you rather see me spending my time developing a beach towel deploying device?

[DanThe]

Unless you drink Carling Black Label you will be wasting your time on the beach towel device

[GeoffBob]

Thank you for the information GeoffBob. I've definately learnt something new today
and bookmarked it becauseI know I'll forget by tomorrow!

You're welcome!

[shalmaneser]

Uwe, I'll say this only one more time: I am sorry I bothered you with a little more technical detail than you wanted. I can assure you it was posted with the best of intentions and I had hoped it would make your work with stretch bolts easier in future. I made a specific effort to present my explanation as clearly and simply as possible. I can also assure you that any corrections to your terminolgy are for the sake of accuracy and certainly not intended to diminish your efforts. Your response to my post was, however, out of line.

OK maybe I had a bad hairday, but I do feel hunted by you whenever I get something a little bit wrong in terms.
I may not know all the nitty gritty details about engineering/math etc but I do have a basic understanding of mechanical components gained over many years through trial and error. It's not that I have never had a strechtbolt in my hands, I was just a little bit courios.

Call me sensitive but I do class your writing style as a little bit partonising/lecturing. Maybe you don't realise this, but remember I am not the only one pointing it out to you.

I do apologise for not honouring your good intentions, but I do not apologise for voicing my opinion.

Jesus Christ man, lighten up. Just because you don't understand the maths doesn't mean it's not relevant. Some of us do, and find it interesting. Some of us don't, and jump to the last sentance to get the gist of the topic. GeoffBob has been nothing but helpful on this forum recently.

As for his 'lecturing style', they're facts. How else can you present them.

Top work once again, GeoffBob.

[UweM3]

Jesus Christ man, lighten up. Just because you don't understand the maths doesn't mean it's not relevant. Some of us do, and find it interesting. Some of us don't, and jump to the last sentance to get the gist of the topic. GeoffBob has been nothing but helpful on this forum recently.

As for his 'lecturing style', they're facts. How else can you present them.

Top work once again, GeoffBob.

well, I am just a humorless german. I will have to live with that.....

[gooner1]

Ah, you're German, Uwe! - I was curious about the ridiculous amount of over-engineering going on with your S50 conversion...

Oiii! What do you mean by over engineering? Form follows function. Would you rather see me spending my time developing a beach towel deploying device?

Would,nt bother Uwe, us Brits would just fire it into the pool anyway. Is there a mathmetical formalae for kissing and making up

[UweM3]

instead of deck chairs and towels I focused on important things.

My redneck stretch gauge!

[ShakeyC]

The purpose of measuring the length and pitch of the threads is so that if for whatever reason you need to remove them and you re-measure it and if its within its tolerance you can safely reuse, so saving you buying another set each time, bonus!

Unlike OE bolts and nuts they shouldn't be re-used as they are not cold rolled steel and will stretch as designed to do.

The way i fit them as recommended by ARP is to cover the thread with ARP assembly lube which normally supplied, wind in the bolts by hand first. Then say you want to tighten them to recommened torque by ARP or for your engine (whichevers correct for you) to do it in 3 stages building up to the required torque setting. An example is 100lb/ft recommened first wind in by hand, torque to 1/4 so 25lb/ft then leave for couple hours. Undo and retorque to 50 lb/ft leave for few hours then undo again and finally retorque to 100 lb/ft you desired. I tend to do it over 3 days leaving as much time as possible for the thread to settle which is the best method.

The reason for undoing and retorque is to allow the metal to settle as it wishes as both ARP and what your screwing into are two different grades of metal they need time to settle and match up. If you straight torqued it to 100 lb/ft after the engines warmed and cooled a few times and went to check the torque it would be drastically lower then 100 lb/ft you originally set it too, if you do as advise this problem shouldn't occur.

Hope that makes sense.

[UweM3]

ShakeyC, the ARP instructions wants the user to torque the bolts 3x up the required full tourque, not in stages. (sure to get there you use stages). And 3 days for fitting rod bolts is what not everybody can afford. That's where a stretch gauage comes in handy.
As you said correctly, the bolt and thread need to form to each other to make sure the correct values are achieved.

A stretchbolt is only longer when fitted, as soon you loosen it up it should be the same length as before (or withing the spec or ARP).
If longer, it's no good anymore. You only supposed to preload the bolt, not stretcht it over it's yield (not sure about the correct engineering term, so just in case....)

[ShakeyC]

Absolutely you can do it one day over few hours, typically with ARP products they advised me and iv checked this to preload in stages as i described previously.

edit- iv double checked for your S50 rod bolts which is different to usual rod bolts 'pro-s series' it does indeed say torque to full 3 times so you are correct!

(ARP said sometimes they advise to torque to ARP or Manufactures torque application dependant, sometimes its different car to car and S50 is one of those odd ones and each instruction supplied is to suit, so i would follow them.)

ARP if within spec can be reused safely, strectch bolts you cannot even if within spec because they will fatigue second time around.

Good luck get building