Torque then 90 degree
- Thread starter S592R
- Start date
jbyrnes
FORD GT OWNER
Don't know, but I heard it differently : The ideal torque for any fastener is " 1) tighten until head snaps off, 2) back off 1/4 turn."
- Dec 3, 2006
- 2,800
Actually I thought it was .... Torque until tight enough that you think it will break the tool(socket, hex or torx bit) of the next person who works on the car .. then add 50nm!! Yes ... I have a collection of broken snap-on tools waiting for my rep.
Simply stated, it is because it is really not about torque - it is about having the right "stretch" of the fastener. Ideally, every time you saw a torque spec, you would see a "stretch" spec. You would install the fastener, torque it, and then remove it to check the stretch achieved. If not enough, then you would install and repeat. Ultimately, you would find the torque that achieved the right stretch. So, which would you publish?
In the torque to "x" and then 90 degrees scenario, the OEM has found that friction may distort torque readings at the desired limit. Therefore, a torque of "x" + 90 degrees gives the desired stretch on the fastener while eliminating friction and/or other variables.
AlohaGT
GT Owner
STORMCAT
GT
MAD IN NC
Proud Owner/ BOD blah bla
If the dealer is good -Ford, If you don't trust him not Ford!
Just insure it is done and welcome back... Nice Gal!
Indy GT
Yea, I got one...too
DBGT-
The Ford/Accufab question has been debated adnausum. Check the multiple previous threads. Bottom line both kits will WORK FINE. Like Mike says, if you are comfortable with a Ford dealer who has a tech who can change out the bolts to your satisfaction, do it! If not get the bolt kit free from Ford with your GT VIN and have a person of your choosing install the kit. Or buy the Accufab kit and have it installed by your preferred installer. Either way the problem is solved.
Actually nota4re has a pretty good explanation of torque-to-yield (TTY) bolts but let me amplify a bit on several of his points. Typical engineering practice is to design a bolted flange with as high a bolt preload as possible based on the bolt material. Typical recommendations are a bolt proof load equal to 90% of the material yield strength. Varying amounts of thread friction which can vary SIGNIFICANTLY by non-use of any lubricants (dry threads) or the use of engine oil, mouse milk, never-seize etc. can significantly alter the bolt load. Thus it it important to follow any factory assembly instructions carefully.
Thus if we design a bolt load to equal 90% of its yield strength (based on bolt tensile area) the bolt will never take a permenent "stretch". Measure the bolt length, install, torque to whatever torque value specified to take the bolt to 90% yield, untorque the the fastener and measure. The bolt will be identical in length as before the install. This is because the bolt was never loaded above its material yield point. This is true for the first torquing or multiple torquings thereafter.
I agree with nota4re, what we REALLY want to know is bolt STRETCH, but this is very difficult to measure instu. About the only application where you can easly measure this stretch is a rod bolt and there are instruments available to make this measurement. Since most applications cannot measure stretch directly we assume a thread friction (which varies with lubricant used) and calculate a bolt load.
When you torque a bolt above the material yield point (ie TTY bolts) you enter a portion of the material stress-strain curve that is not linear (meaning a given strain or bolt stretch no longer returns a linear amount of material stress or load) and the bolt load produced for a torque above yield is even less reliable at predicting actual load developed by the fastener. For this reason, torquing specs in this plastic/non-linear region of the bolt material strength are usually specified as an initial amount of torque to take the load up to near yield and then an additional angle-of-turn afterward to load the bolt into the non-linear bolt strength region.
It was stated, and is true, the six Accufab outer diameter fasteners on our rear axle half shafts come with standard torque callouts (resulting in below material yield stress) whereas the Ford specified bolts are TTY. My preference for this bolted assembly is the TTY bolt as for a given bolt size a higher preload can be achieved with a TTY fastener. Again though, both kits will adequately address the previous inner bolt failures.
Hope this was not too technical and helped in understanding.
The Ford/Accufab question has been debated adnausum. Check the multiple previous threads. Bottom line both kits will WORK FINE. Like Mike says, if you are comfortable with a Ford dealer who has a tech who can change out the bolts to your satisfaction, do it! If not get the bolt kit free from Ford with your GT VIN and have a person of your choosing install the kit. Or buy the Accufab kit and have it installed by your preferred installer. Either way the problem is solved.
Actually nota4re has a pretty good explanation of torque-to-yield (TTY) bolts but let me amplify a bit on several of his points. Typical engineering practice is to design a bolted flange with as high a bolt preload as possible based on the bolt material. Typical recommendations are a bolt proof load equal to 90% of the material yield strength. Varying amounts of thread friction which can vary SIGNIFICANTLY by non-use of any lubricants (dry threads) or the use of engine oil, mouse milk, never-seize etc. can significantly alter the bolt load. Thus it it important to follow any factory assembly instructions carefully.
Thus if we design a bolt load to equal 90% of its yield strength (based on bolt tensile area) the bolt will never take a permenent "stretch". Measure the bolt length, install, torque to whatever torque value specified to take the bolt to 90% yield, untorque the the fastener and measure. The bolt will be identical in length as before the install. This is because the bolt was never loaded above its material yield point. This is true for the first torquing or multiple torquings thereafter.
I agree with nota4re, what we REALLY want to know is bolt STRETCH, but this is very difficult to measure instu. About the only application where you can easly measure this stretch is a rod bolt and there are instruments available to make this measurement. Since most applications cannot measure stretch directly we assume a thread friction (which varies with lubricant used) and calculate a bolt load.
When you torque a bolt above the material yield point (ie TTY bolts) you enter a portion of the material stress-strain curve that is not linear (meaning a given strain or bolt stretch no longer returns a linear amount of material stress or load) and the bolt load produced for a torque above yield is even less reliable at predicting actual load developed by the fastener. For this reason, torquing specs in this plastic/non-linear region of the bolt material strength are usually specified as an initial amount of torque to take the load up to near yield and then an additional angle-of-turn afterward to load the bolt into the non-linear bolt strength region.
It was stated, and is true, the six Accufab outer diameter fasteners on our rear axle half shafts come with standard torque callouts (resulting in below material yield stress) whereas the Ford specified bolts are TTY. My preference for this bolted assembly is the TTY bolt as for a given bolt size a higher preload can be achieved with a TTY fastener. Again though, both kits will adequately address the previous inner bolt failures.
Hope this was not too technical and helped in understanding.
- Dec 3, 2006
- 2,800
We need an exploding brain emoticon.
So now that I am significantly less confused, more or less than before, but not as much as I was yesterday, but significantly more than I was the day I was born, and yet less than the moment that I got this cerebral hemorrage trying to figure out which bolt to use on my car, but not as much as I was before I asked the remaining question that I dare to ask. Can a TTY bolt be reused if it is over torqued due to operator error, or rather to say the technician that comes into review some previous work removes the bolt without knowledge of the previous installation?
I think I am going to go buy a set of accufabs and mix them with the ford kit just to play russian roulette. :bored
So now that I am significantly less confused, more or less than before, but not as much as I was yesterday, but significantly more than I was the day I was born, and yet less than the moment that I got this cerebral hemorrage trying to figure out which bolt to use on my car, but not as much as I was before I asked the remaining question that I dare to ask. Can a TTY bolt be reused if it is over torqued due to operator error, or rather to say the technician that comes into review some previous work removes the bolt without knowledge of the previous installation?
I think I am going to go buy a set of accufabs and mix them with the ford kit just to play russian roulette. :bored
Indy GT
Yea, I got one...too
Very intersting question and one that is certainly relavent!
In my engineering opinion, you can reuse a TTY fastener I would say up to 5 additional torquings. Now this is contrary to what the OEM will tell you. They will say the bolts are one time use only. However, an engineering discussion of the topic will not support the suppositon that the bolts are no good after one torquing above yield. Especially for high grade fasteners with good material elongation.
Now you do use the term "over torqued" so I guess I should qualify my above answer. If instead of turning the head 90 deg as is specified in the Ford tightening procedure some gorilla twists the bolt head a full 360 deg after the initial torque, well then yes the bolt is no good (if the head stays on). But if tech1 started your bolt replacement job and midway through the job got sick and went home, and tech2 picked the job up and did not know if the bolts had been properly torqued and turned 90 deg, so he loosened the bolts and retightened to the Ford procedure, then I think they are fine.
That is a very good question!
In my engineering opinion, you can reuse a TTY fastener I would say up to 5 additional torquings. Now this is contrary to what the OEM will tell you. They will say the bolts are one time use only. However, an engineering discussion of the topic will not support the suppositon that the bolts are no good after one torquing above yield. Especially for high grade fasteners with good material elongation.
Now you do use the term "over torqued" so I guess I should qualify my above answer. If instead of turning the head 90 deg as is specified in the Ford tightening procedure some gorilla twists the bolt head a full 360 deg after the initial torque, well then yes the bolt is no good (if the head stays on). But if tech1 started your bolt replacement job and midway through the job got sick and went home, and tech2 picked the job up and did not know if the bolts had been properly torqued and turned 90 deg, so he loosened the bolts and retightened to the Ford procedure, then I think they are fine.
That is a very good question!
fjpikul
GT Owner
Mouse milk? Is this some kind of lubricant or sealant I've never heard of? A secret engineers trick (like drinking Shirley Temples)?
Please explain what "very difficult to measure instu." means. Are you mispelling in-situ?
Obviously working at home with all that wine at easy access is affecting your ability to type.
Please explain what "very difficult to measure instu." means. Are you mispelling in-situ?
Obviously working at home with all that wine at easy access is affecting your ability to type.
- Dec 3, 2006
- 2,800
what is the difference other than torque ... if the settings are suppose to be 25 then 90 degrees and someone torques to say 30? See where this is all just too nuts for the average joe on the wrench? Why is arp's torqued to 80?
AHHHHHHHHH :willy:willy:willy:willy:willy:willy I need a drink. :beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::screwy::screwy::screwy:
AHHHHHHHHH :willy:willy:willy:willy:willy:willy I need a drink. :beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::beer2::screwy::screwy::screwy:
Uhhhhhhhhhhhhh...sir? Uhhhh, just buy a set of Accufabs or a set of the new Ford 'bolts...install 'em per instruckshuns ... TOSS the old ones in the nearest enviornmentalist approved trash can ... and all these questions become moot from that moment forward...
Some of life's issues ARE solved that easily.
You're welcome...
(Pockets, That Marine will NOT be buyin' yew din-din in 'Vegas now, yew idiot.)
Indy GT
Yea, I got one...too
Pockets, I agree!
DBGT don't make this more complicated than it needs to be. Just install either kit per recommendations.
Quick answer, if you start at 30 then 90deg instead of 25 then 90 you will wind up stretching the bolt more, possibly than intended. At these values I would think it OK. And no this is not more complicated for the average joe. If you know how to use a torque wrench and have a breaker bar for the turn-of-nut, it is a piece of cake. ARP determines the torque of their bolt based on their assessment of: thread friction, proof load desired, material properties, etc. Go to their website for more info on their bolts:
http://www.arp-bolts.com/Tech/Tech.html
Frank as always thanks for being my ever-present thesaurus. Where would I be without you buddy!!! Mouse milk, go ask an aircraft mechanic. That's who I learned it from...
DBGT don't make this more complicated than it needs to be. Just install either kit per recommendations.
Quick answer, if you start at 30 then 90deg instead of 25 then 90 you will wind up stretching the bolt more, possibly than intended. At these values I would think it OK. And no this is not more complicated for the average joe. If you know how to use a torque wrench and have a breaker bar for the turn-of-nut, it is a piece of cake. ARP determines the torque of their bolt based on their assessment of: thread friction, proof load desired, material properties, etc. Go to their website for more info on their bolts:
http://www.arp-bolts.com/Tech/Tech.html
Frank as always thanks for being my ever-present thesaurus. Where would I be without you buddy!!! Mouse milk, go ask an aircraft mechanic. That's who I learned it from...
Last edited:
- Dec 3, 2006
- 2,800
I love you guys !!!! :biggrin:bored
The car has the new Ford kit on it ... I'm just a bit leary of the whole TTY thing. Think I'm gonna call Accufab and get the arp bolts. The inside of the Ford repair looks fine .... I just have a malfunction when it comes to the others. :thumbsdow
I have visions of a couple of years from now doing something in the back and having a retorqued bolt fail. :ack:ack:ack Probably irrational .. but when has a Marine ever been accused of being rational. We like to hit things with big heavy lethal things for fun.
And Pockets ... this Marine will gladly pick up your din din tab any time.
The car has the new Ford kit on it ... I'm just a bit leary of the whole TTY thing. Think I'm gonna call Accufab and get the arp bolts. The inside of the Ford repair looks fine .... I just have a malfunction when it comes to the others. :thumbsdow
I have visions of a couple of years from now doing something in the back and having a retorqued bolt fail. :ack:ack:ack Probably irrational .. but when has a Marine ever been accused of being rational. We like to hit things with big heavy lethal things for fun.
And Pockets ... this Marine will gladly pick up your din din tab any time.
Indy GT
Yea, I got one...too
It's a sickness......I know....and appologize....
Just try to bear with me (and humor me as only Frank does....)
Just try to bear with me (and humor me as only Frank does....)