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All Bolts/Nuts when installed properly require proper Torque. Keep in mind that torque is NOT Bolt Tension or Clamping Force. Torque is an indication of the required Bolt Tension/Clamping Force when used with a calibrated Torque Wrench. Torque of a fastener in a given application is usually specified by the design engineers. Many fasteners require a direct torque value. Many of the bolts/nuts on our Cummins are of this type. However, other bolts in specific applications require "TTY" Torque to Yield Fasteners.

Torque to Yield Fasteners are used in high stress areas such as Head Bolts, Connecting Rods and Crankshafts as a brief example. Torque to Yield are required to achieve the specific preload. The process of torquing TTY Bolts is called 'Torque to Angle'. Torque to Angle is used in assemblies in the Cummins Engines.

TTY Bolts are designed to stretch slightly when installed. This process allows for more even loading and allows the bolts to hold torque better. Cummins allows the re-use of TTY bolts as long as they are not stretched past a Cummins Spec Limit. As an example, Cummins sells a tool to measure the length of head bolts ( Cummins PN# 3823921 ' Cap Screw Length Gauge'). This gauge will quickly tell you if the bolt has been stretched to much past yield. If the bolt does not pass the Gauge Test, it should be discarded.

When TTY bolts are installed, they are tightened to a specific torque in a given sequence, then tightened to an additional amount that is measured in degrees of rotation. This final twist in degrees of rotation provides the stretch to bring the bolt to its yield point and creates the needed elastic clamping force. The stretch is only a few thousands of an inch. Re-using TTY bolts will cause the bolt to stretch further. This is why Cummins has the Cap Screw Length Gauge and gives the Maximum length spec. A bolt that is stretched past the design limits will no longer hold the same torque load as before and it can fail.

If your doing Engine work on your Cummins, a Torque Angle Gauge is absolutely required to bring the TTY 'Torque to Yield' bolts to spec. The Cummins Torque Angle Gauge is rather expensive, much more economical versions are available at better auto parts suppliers. Fel Pro (The gasket people) make a cheap plastic Torque Angle Gauge that will work just fine.
Fel Pro calls it the Torque Angle Indicator # TRQ-1.

Also, Torquing a TTY bolt to a given torque will not give the same Clamping Force that the Torque to Angle does. As an example; Cummins, in the shop manual for many fasteners give the correct Torque to Angle sequence, if the Torque to Angle was not so critically important, they would just have listed to torque to xxx ft lbs and be done with it.

Proper use of fasteners is critical in what we are doing. A few weeks ago, a friend proudly told me he used all new Grade 8 fasteners on his entire truck project. Well, this is not correct. Different applications require different Grade Fasteners. Grade 8 can not automatically blessed as being best all around. Grade 5 may be the best choice in some applications.

The formula for determining torque is Torque= k x d x f. May I suggest for additional reading, to learn how the 'K' part of the equation is so critical to you, go to the following web site. This web site is the Fastenal Corporation Site. You want to down load the Fastenal Technical Reference Guide 2000 PDF file 801KB. This 54 page document will tell you 'everything' you will ever need to know about fasteners, torque control, re-use of bolts, choosing the proper grade fastener for a given job and much more. Its a wealth of information. The URL is;

http://www.fastenal.com/web/resourcesAction.ex?action=DocLib

Sorry to be so lengthy, but this is important to understand when rebuilding our engines.

Paul
 

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I'm curious as to why you've said a grade 5 fastener may be better than a grade 8 in some applications?

In a TTY application or something to break away in case of overload I could understand why. But I'm struggling to think of any others.
 

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Paul great article and much appreciated. Not sure if you saw but I posted this in the performance section:
http://www.4btswaps.com/forum/showpost.php?p=117&postcount=4

Supposedly according to some guys on TDR that if you simply torque to 125 ft/lbs (off the top of my head, I will need to double check) instead of the torque then 1/4 turn method described in the manual, head gaskets last longer? When I redid the head on my last 4BT(A), the head gasket kit came with a tool for measuring bolt stretching. I am pretty sure it was the first head gasket, luckily it had a lot more room for stretching..
 

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Discussion Starter #4
Andre;

Yup. many people develope shortcuts, right or wrong and swear by them. I bet some person did the torque to angle and then tested the bolt torque with a torque wrench. Raising the torque till it clicked and then saw the indicated torque was xxx. The Fastenal Tech Ref also talks about calibrated torque wrenchs and accuracy. Years ago, I worked for a International Company that had a department just to calibrate torque wrenches and torque screw drivers. The certification was only valid for 30 days, and void if the device was dropped. It was a continous program of certification and testing. Now, I know and realize we cant do this, but it does show the importance of accurate torque.

Paul
 

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Discussion Starter #5
Dougal;

You really need to read and understand the Fastenal Tech Ref. It expains in detail selecting the proper bolts for a joint type ie; Shear Joint, Tension Joint. Its way to much for me to type here with my old fingers. The Fastenal Document should be kept in your shop drawer for reference in fasteners.

I bought a Draw Tite Gooseneck Hitch for my Dodge Ram. Its rated for 30,000#. The .500" bolts supplied to bolt her down are Grade 5. Figureing they were sent in error, I called Draw Tite. They told me Grade 5 are required as they wont shear or snap if bent some as a G8 in the same application. He also suggested I down load the Fastenal Doc LOL!. The link for the Fastenal Document is listed in my post above.

Paul
 

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Dougal;

You really need to read and understand the Fastenal Tech Ref. It expains in detail selecting the proper bolts for a joint type ie; Shear Joint, Tension Joint. Its way to much for me to type here with my old fingers. The Fastenal Document should be kept in your shop drawer for reference in fasteners.

I bought a Draw Tite Gooseneck Hitch for my Dodge Ram. Its rated for 30,000#. The .500" bolts supplied to bolt her down are Grade 5. Figureing they were sent in error, I called Draw Tite. They told me Grade 5 are required as they wont shear or snap if bent some as a G8 in the same application. He also suggested I down load the Fastenal Doc LOL!. The link for the Fastenal Document is listed in my post above.

Paul
I just read the Fastenal tech ref, understanding it isn't a problem. Other than everything being in ft/lb and inches it's quite similar to many of my old engineering text books. I couldn't see anything in there about using a fastener which exceeded the strength required.

Your drawhitch is an interesting example, are the mounts not strong enough to take a higher strength bolt?
 

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I just read the Fastenal tech ref, understanding it isn't a problem. Other than everything being in ft/lb and inches it's quite similar to many of my old engineering text books. I couldn't see anything in there about using a fastener which exceeded the strength required.

Your drawhitch is an interesting example, are the mounts not strong enough to take a higher strength bolt?
I think what they were implying is even though the GR 8 fasteners have a higher tensile strength, if they fail they will fail with no warning, ie a sudden fracture. A GR 5 fastener has more ductility and will give a little bit before it fails so maybe they consider that the better option?
 

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Discussion Starter #8
52Wrench...absolutely right !

In a tension join application, G8 fasteners have great strength and are the fastener of choice, where strength is required. In a Shear Joint application, where shear forces are present or even a possible bending force, the harder G8 can crack and fail where a G5 will not fail as quickly. This is known as Ductility of a fastener. You may find by looking at bolt tables that; as an example, a G8 3/8" bolt will exhibit the strength you want for a joint. However the joint is in shear or bending so a G5 is required. The G5 may have to be a 7/16" to exhibit the required strength. There are even places where a G2 is all that is needed, areas of non structural strength such as mounting accessories etc. Higher strength bolts are not needed and a waste of money.

In the future, as you purchase items for your trucks, look at the bolt/nut grade supplied by the manufacturer. In many cases you will find G5 supplied. They are not cutting corners, trying to save a buck, but rather its the fastener of choice for that application.

Try a simple test. Take a 3/8" G5 and a 3/8" G8 bolt 5 inches long. Put them both in a large strong vise. Take a piece of 14", 3/4" pipe and stick it over the G8 bolt. Put your gloves and safety glasses on and see how far you can bend the G8 bolt before it fails. The do the same on a G5. You will find that the G5 will bend more before failure since its not so hard. The same would be true in shear, but we cant test that in our shops.

Those hitches I mentioned........I have always worried about them. Probably made in West Mongolia out of melted down Yak Carts LOL

Paul
 

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Grade 8's don't fail without warning. Even metric grade 14.9 cap screws don't fail in a brittle manner without warning.

Grade 5 starts to yield at roughly 90,000ksi and fails in tension at 120,000ksi
Grade 8 starts to yield at roughly 120,000ksh and fails in tension above 150,000ksi.

Both have the same window of ductility between yield and failure, but the grade 5 will have already broken by the time the grade 8 starts to yield.


What do you mean by loading bolts in shear?

In all bolted joins, the bolt is used as a clamp, shear forces are taken by friction between the faces.
A bolt will only see shear force if the joint comes loose. If that has happened then the joint has already failed and probably damaged the fasteners.
 

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Discussion Starter #10
Page 3, 'shear strength' in the Fastenal Tech Ref explains shear joints.

We are going to have to agree to disagree on this, and move on. We are using valuable bandwidth.

Paul
 

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Paul and Dougal, let me commend the both of you on agreeing to disagree. This is my first post as a brand new member to this forum. As I read this thread I thought "Oh No! not another feud site with endless battles for intellectual supremacy". I am a nubie, but I am also a mature adult. I enjoy learning from both sides of a discussion (but not a flaming argument). It helps to spur my own curiosity and desire to research the topic on my own.
My point is this, I have come here to seek out knowledge I do not yet possess, share in others' triumphs, and support those who are trying to accomplish the same. I've have a early bronco/4BT project of my head for over 8 years and am now in a position to act on it. From what I have read on the yahoo site and this forum, I am good company and look forward to reading all that you have to offer and hopefully share some of my own knowledge where appropriate
Keep up the good work!
 
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