Dodge Cummins Diesel Forum banner

1 - 20 of 37 Posts

·
Registered
Joined
·
47 Posts
Discussion Starter #1
Fastenall has 12.9 class m12 threaded rod available, and also the nuts.. Now has anyone considered making your own studs? Can't see why this wouldnt work? Thoughts?
 

·
Premium Member
Joined
·
520 Posts
Probably not worth the time/money it saves if it fails?? Does make sense though
 

·
Sasquatch
Joined
·
3,631 Posts
Sure, you can make your own studs. But do you think you can create a set of studs that matches the properties and quality of ARP or Extreme Studs for the same cost or less?
 

·
Registered
Joined
·
47 Posts
Discussion Starter #4
Are ARP studs threaded fully or no?

And no I can't match their quality per say but makes me wonder if their threads are roll formed or cut, makes a big difference.

Either way I guess my made up studs would be a step above bolts....
 

·
Armchair Mechanic
Joined
·
1,583 Posts
Are ARP studs threaded fully or no?

And no I can't match their quality per say but makes me wonder if their threads are roll formed or cut, makes a big difference.

Either way I guess my made up studs would be a step above bolts....
They are not threaded fully and have coarse thread on the block end and fine thread for the 12pt nuts.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #6
Here is a pic of standard thread bolt engagement... Which is not much!! I'm going to add 10mm to each bolt and run new holo krome socket head cap screws.
each stock head bolt only gives you 20mm of engaged threads.
Although in engineering terms you only need a small % of engaged threads... Still it doesn't sit well with me.
 

Attachments

·
Registered
Joined
·
884 Posts
Are ARP studs threaded fully or no?

And no I can't match their quality per say but makes me wonder if their threads are roll formed or cut, makes a big difference.
I almost guarantee they are rolled threads. It's faster and cheaper than cutting threads.
 

·
Registered
Joined
·
78 Posts
From my understanding part of what makes the arp's superior is that they use fine thread for the top of the stud. Gives a more consistent torque and clamping force. If you just want a cheap upgrade, you can use a set of the Allen headed cap screws that are rated 12.9
 

·
Premium Member
Joined
·
640 Posts
I can't address the quality of the Fastenal threaded rod. Rolled threads can have denser and smoother surfaces than cut ones. Torque is just an inexpensive way to measure tension in the fastener (clamping force). Torque is also a function of rotational friction so smoother threads and nut and washer faces are better. Due to the physics of inclined planes fine threads on one end of the stud allows better control of clamping force versus torque. One advantage of studs (or threaded rod and nuts) is that they can be fully engaged into the block before they have any tension on them. This makes the torsional friction a function of the threads and nuts instead of the threads and the cast iron threads in the block. It also preserves the threads in the block and vastly reduces the error induced by the twisting of the fastener even with coarse threads on both ends.
From what I have read the stock bolts are designed as single use bolts (torque to yield on initial assembly?)

Keep the rod cool when you cut it and clean up the ends so you don't alter the tempering. You could do some testing with a short length of rod through a steel plate with nuts and washers on both ends to get a feel of how tough the Fastenal rod is.

I've never had a head off a Cummins but chances are that a bottom tap run into the block could let you run the rod into the block a few more turns. This may not be necessary but if I was going to this trouble I'd feel better for doing it.
 

·
Registered
Joined
·
47 Posts
Discussion Starter #11
Yes that is correct info.. Now I've learned towards a 10mm longer holo krome bolt, because the threaded rod is damn near the same cost as the ARP studs. I've bottom tapped the head holes with at least 4-5 turns more, the only thing you have to watch is the grip lenghth of the bolt. Bit of measuring and I've found they will not interfere with anything.
Working on different main bolts now too, I also bottom tapped them and want to run +10mm... Fun stuff
 

·
Registered
Joined
·
364 Posts
I can't address the quality of the Fastenal threaded rod. Rolled threads can have denser and smoother surfaces than cut ones. Torque is just an inexpensive way to measure tension in the fastener (clamping force). Torque is also a function of rotational friction so smoother threads and nut and washer faces are better. Due to the physics of inclined planes fine threads on one end of the stud allows better control of clamping force versus torque. One advantage of studs (or threaded rod and nuts) is that they can be fully engaged into the block before they have any tension on them. This makes the torsional friction a function of the threads and nuts instead of the threads and the cast iron threads in the block. It also preserves the threads in the block and vastly reduces the error induced by the twisting of the fastener even with coarse threads on both ends.
From what I have read the stock bolts are designed as single use bolts (torque to yield on initial assembly?)

Keep the rod cool when you cut it and clean up the ends so you don't alter the tempering. You could do some testing with a short length of rod through a steel plate with nuts and washers on both ends to get a feel of how tough the Fastenal rod is.

I've never had a head off a Cummins but chances are that a bottom tap run into the block could let you run the rod into the block a few more turns. This may not be necessary but if I was going to this trouble I'd feel better for doing it.
I agree with everything being said here except that bit about inclined planes. The thread is 60 degrees in both the course and fine, vector is the same in both cases. The advantage of fine thread is they can support higher clamping forces because of increased surface area, but only about 10%. The thread engagement on the top is limited by the nut, that's why they're fine thread. More threads in given distance.
 

·
Supporting Vendor
Joined
·
8,229 Posts

·
Premium Member
Joined
·
640 Posts
I agree with everything being said here except that bit about inclined planes. The thread is 60 degrees in both the course and fine, vector is the same in both cases. The advantage of fine thread is they can support higher clamping forces because of increased surface area, but only about 10%. The thread engagement on the top is limited by the nut, that's why they're fine thread. More threads in given distance.
The pitch of the thread is the inclined plane to which I refer. Neglecting friction the ratio of tension in the fastener to the torque is proportional to the pitch. A finer pitch thread has more mechanical advantage thus more tension for a given torque.
 

·
The Uppity 12v Admin
Joined
·
8,216 Posts
defiantly not worth the risk.
I would have said "definitely" myself, but I think "defiantly" is also acceptable given the topic. :hehe:

Fasteners are the last place a person ever wants to skimp. Not only on head bolts, but in life in general. Not when you can get over 500hp with daily-driver reliability on a $65 set of generic socket head cap screws.

I'll also cite Will's experience with factory bolts. I can't remember what his horsepower was, but the Junker didn't lose it's first (original) gasket until 26 degrees of timing and 80 psi boost or something like that, with many, many runs down the strip.
 

·
Registered
Joined
·
364 Posts
The pitch of the thread is the inclined plane to which I refer. Neglecting friction the ratio of tension in the fastener to the torque is proportional to the pitch. A finer pitch thread has more mechanical advantage thus more tension for a given torque.
I understand. The "inclined plane" is the thread contact: which is the same in both cases. You're correct, a fine thread indeed has greater mechanical advantage. But you don't just torque a fine thread to 90 ft lbs and it somehow magically becomes a larger torque value on a coarse thread? 90 ftlbs is 90 ftlbs. The difference is you gotta turn a fine thread farther before you reach that value. More thread engagement, more surface area, more holding capacity. Clamping force is the same. Torque is just a convenient method of estimating elongation because there is friction between the threads proportional to the force when the stud stretches. Torque means nothing if it weren't for friction. Torque doesn't hold things together. Example: I thread and eye bolt into a 100lb baseplate. I pick it up with the crane. I can add 50lbs and the threads rip out and the baseplate comes crashing down. Now I torque the eyebolt in to 100ftlbs. Pick up the plate. 50 lbs and it comes crashing down. The elongation of the fastener creates the clamping force, and that is only created by rotation. The reason torque and rotation can be related is because of friction, hence why they give you lube and tell you to clean the threads: they want to control the coefficient of friction so what they tell you to torque it to results in the correct clamping force. Look at a cummins head bolt. Torque value plus 90 degrees. Degrees. Not torque. "Inclined plane" is not a factor. I'm not trying to be a you know what about it, but I'm trying to prevent spread of misinformation. ARP uses a fine thread because they have more holding capacity than a course thread over the height of the nut. Not because it changes the final torque, not because of any "inclined plane", not because of mechanical advantage.
 

·
Premium Member
Joined
·
640 Posts
I understand. The "inclined plane" is the thread contact: which is the same in both cases. You're correct, a fine thread indeed has greater mechanical advantage. But you don't just torque a fine thread to 90 ft lbs and it somehow magically becomes a larger torque value on a coarse thread? 90 ftlbs is 90 ftlbs. The difference is you gotta turn a fine thread farther before you reach that value. More thread engagement, more surface area, more holding capacity. Clamping force is the same. Torque is just a convenient method of estimating elongation because there is friction between the threads proportional to the force when the stud stretches. Torque means nothing if it weren't for friction. Torque doesn't hold things together. Example: I thread and eye bolt into a 100lb baseplate. I pick it up with the crane. I can add 50lbs and the threads rip out and the baseplate comes crashing down. Now I torque the eyebolt in to 100ftlbs. Pick up the plate. 50 lbs and it comes crashing down. The elongation of the fastener creates the clamping force, and that is only created by rotation. The reason torque and rotation can be related is because of friction, hence why they give you lube and tell you to clean the threads: they want to control the coefficient of friction so what they tell you to torque it to results in the correct clamping force. Look at a cummins head bolt. Torque value plus 90 degrees. Degrees. Not torque. "Inclined plane" is not a factor. I'm not trying to be a you know what about it, but I'm trying to prevent spread of misinformation. ARP uses a fine thread because they have more holding capacity than a course thread over the height of the nut. Not because it changes the final torque, not because of any "inclined plane", not because of mechanical advantage.
You are missing the point entirely. For the same torque a finer pitch thread will put more tension in the fastener than a coarser one for the same reason it is easier to push a car up a shallow incline than up a steep one. This is my last post on the subject. I am right and I see no profit in arguing with you. Review your Statics book.
 

·
Registered
Joined
·
3,024 Posts
I would have said "definitely" myself, but I think "defiantly" is also acceptable given the topic. :hehe:

Fasteners are the last place a person ever wants to skimp. Not only on head bolts, but in life in general. Not when you can get over 500hp with daily-driver reliability on a $65 set of generic socket head cap screws.

I'll also cite Will's experience with factory bolts. I can't remember what his horsepower was, but the Junker didn't lose it's first (original) gasket until 26 degrees of timing and 80 psi boost or something like that, with many, many runs down the strip.
And some fail @25# boost that are on the original just driving around.
 

·
Supporting Vendor
Joined
·
8,229 Posts
There are a few pullers that have used stock head bolts doing much more than 80PSI. They do check their bolts very often and replace them when they don't torque right. I know there are some companies that sell these 12.9 bolts and have decent luck. I guess a better questions is "Is it worth the effort?" and "how much is the cost of failure?"

I am sure some have tried the 12.9 studs. I would like to see them post their experiences and move from a theoretical discussion.
 

·
Registered
Joined
·
364 Posts
If any mods happen to be watching this thread, I wish to make it clear my intention here is not to flame or put down anyone else for their opinion, but there is a clear misunderstanding here on fine and course thread pitches that should be addressed. I don't like bickering, and I can explain myself better with pictures than I can in trying to lead someone down a logical path. The assertion that a fine thread gives a higher clamping load than a coarse thread at the same torque is false. And I definitely don't want a future aspiring Cummins engineer to read this thread and think that if he uses bolts with an infinitesimally small thread pitch, he can call out for all these bolts to be simply hand tightened and hold the engine together because their finer pitch gives a higher clamping load. Not at all true; a common misconception.

I'm just going to assume that people who believe in this are doing so under the premise of mechanical advantage in an inclined plane. That a shallower angle on a wedge makes it easier to lift a heavy object. This is true, but not applicable here. Why? Because the angle of this envisioned "wedge" is the same in fine and coarse thread: 60 degrees, and its the same in all Unified Threads. This image is taken from Wikipedia on "Unified Thread Standard"



Here's a drawing of exactly what's going on here. Please excuse my five year old colored pencil drawings... as that's stretching the limit of my artistic talent. Coarse threads on the left and fine on the right.



Now let's imagine we're trying to push our miniature Cummins up the side of the threads for both cases. The force required to push our truck on a friction-less surface is dependent on only it's weight, and the angle of our inclined plane. We're going to assume our truck doesn't gain or lose weight switching from one to the other, and since the angle of both threads are the same, its pretty easy to see that the force we need to push our truck up is the same. Fine threads offer no advantage here, and you will see this is analogous in the torque scenario.



What does make a difference between the two cases is "work", which is what the term mechanical advantage refers to. Work, in simple form, is the product of force and distance. The work I'm doing pushing a 10lb box 10ft is 100 ftlb. Simple enough. Let's look at the work we're doing moving our truck up the threads.



Here, the fine thread is drawn to have half the pitch of the coarse thread. Since we already know that the force we need to move the truck is the same, what we care about is distance. Maintaining the same angle of inclination, the geometry of the threads will mean that our distance up the inclined plane, labeled as "x", is half as long in the fine thread screw as the coarse thread screw. This means, moving our truck up one fine thread requires half as much work as moving our truck up one coarse thread. Although this is a great simplification of actual thread design, it still has the same basic principle.



Now, bolts and studs hold things together with a clamping force. The ONLY thing that generates this clamping force is elongation of the fastener. And the elongation of the fastener is a direct function of the thread pitch. In this example we'll use a simplified set of 1/4" coarse and fine thread bolts, imagining them as equal diameter cylinders that start out 1" long.



Figuring out how much we are stretching the bolt in one turn is very simple. If it has 20 threads in 1 inch, that means each thread is .050" apart. Its just the reciprocal, 1 divided by 20. So after 1 turn of a 1/4-20 bolt that starts out 1" long, its now stretched to 1.05" long. Our 1/4-28 bolt becomes 1.036" long after one full turn.



Now we need to calculate clamping force after 1 turn. There are a few assumptions we need to make here. The first is that the bolt is still within its elastic region of the stress-strain curve. This allows us to use a property called "Modulus of Elasticity" to calculate stress for a given change in length. We're going to choose an arbitrary value for this: 100,000 psi. This is actually quite small, and what its effectively saying is that if we stretch a bolt that was initially 1" long an additional inch, the tensile stress the bolt is subjected to is going to be 100,000 psi. In the following picture, F is the clamping force, A is the cross sectional area of our bolts which is the same in both cases (in reality these are slightly different), E is our modulus of elasticity, Li is the initial length of our bolt, and delta L in the numerator is our change in length.



After calculating, in one revolution of the coarse thread bolt we have created 245lbs of clamping force, and in one revolution of the fine thread bolt we have created only 175lbs of clamping force. And you can see looking at the picture, the ratio of these forces is equal to the ratio of the thread pitches. To put it plainly, the clamping force in one revolution is directly proportional to the thread pitch for bolts of equal nominal diameter and material strength.



But we all use torque values when tightening bolts, we don't actually measure the clamping force. So how does torque relate to all this? And that is very simple: friction. The overwhelming reason there is torque present at all when turning our bolts is because of friction. And it's very important when for torque specifications. When ARP gives you lube, and tells you to ensure the threads in the block are totally clean, they are trying to control what's known as the coefficient of friction. Dirty or damaged threads will increase this coefficient, and that will in turn require more torque on our bolts to reach a specific level of stretch: which is what we really want for consistent clamping. In our example, this coefficient is assumed to be 0.2



If you were paying attention to the vectors in my first sketch with the inclined plane, you will see they reappear here. We need it to determine what's known as the "normal force", which is amount of our clamping force that is pushing against the threads. This is dependent on the angle of inclination, which is still 30 degrees. But, we've already calculated that our clamping force in one turn of the bolt is different from coarse to fine. This means the frictional force will be different as well. Something that needs to be kept in mind about forces of friction: the value we are calculating is actually the maximum force friction can resist before motion occurs. So a cardboard box just sitting on the floor isn't subjected to any frictional force until you try to push it, and if you push with less force than the maximum value of friction, it simply doesn't move. It exerts an exactly equal and opposite force to you up until the point that you push harder than its maximum value. Keep this in mind. Pay attention to the bottom portion of this picture. Here I've calculated the frictional force underneath the bolt head that's pressing against the block.



Now we can actually go about calculating how much torque it takes to spin this bolt one revolution. Torque is technically not even the correct term to be using, as the formal definition of torque includes an angular acceleration. What we're actually all talking about when we "torque" something with a torque wrench is "moment." Moment is just the product of force and distance, but we can call it torque because that's what everyone else calls it.



Here we're going to make a simple assumption that the resisting torque to us trying to spin the bolt with our wrench is the frictional force multiplied by the radius of the bolt head. A 1/4" cap screw has a 7/16" head across the flats, so we'll just use 7/32" as our radius. You can see that I've used the higher friction force from underneath the bolt head in calculations of torque. I do not use the lower value from the threads, nor do I add them together, because remember friction is a maximum force. In the majority of cases, this will be under the bolt head, but not always. So it turns out we need 10.7 in-lbs to overcome friction for the coarse thread, but only 7.6 in-lbs to overcome friction with the fine thread (I told you it was a weak bolt). However, remember these bolts are NOT under the same clamping force at one turn.



So now let's answer the question: at 20 ft-lbs for a coarse and fine thread bolt or stud, which one has more clamping load. We've set our torque value, and we will again use a 1/4" bolt, but this time with some more realistic numbers. We will now do the calculation we just made for torque in reverse, instead solving for the maximum frictional force that the bolt is resisting with.



Dividing our torque value by the radius of the bolt head (careful to convert inches to feet since we are using ft-lbs here), we find that the resisting frictional force at 20 ft-lbs is 1097 lbs. Now, again we work backwards in the previously given example of finding friction under the bolt head to find the normal force, which is also equal to the clamping force. We find that in the course thread case, we have 5485 lbs of clamping force when torqued to 20ft-lbs.

Now let's look at the fine thread bolt.



...The frictional force is the same. Well of course it is, we didn't change anything else in the problem so it should be just the same as the coarse case. This means the normal force, and the clamping force, and hence the elongation of the bolts are also the same. So here, we have theoretical proof: fine and coarse threads of the same size bolt have the SAME clamping force for a given torque. Why, because clamping force is dependent on elongation, and for a given torque elongation is the same!



But that would beg the question, how does fine thread offer any advantage at all? The reason is work. To determine how much work it takes to rotate a fine thread screw vs a coarse thread, first we need to know how much we actually turned our bolts when our torque wrench clicked at 20ft-lbs. As it turns out, the ratio of elongation to the pitch is equal to the ratio of how much we've rotated our bolt to a full 360 degrees.



So here we see the difference. We reach 20 ft-lbs of torque on the course head bolt after 29 degrees of rotation, where we don't reach 20 ft-lbs of torque until we've rotated our fine thread bolt 40 degrees. We have to rotate the fine thread bolt farther to reach the same torque/same clamping force as we do with the course thread.



At first this doesn't seem advantageous, quite the opposite actually. But when you consider work is how much force you exert over a given distance, you can see how a fine thread actually requires less work per turn, just as it required less work to push our Cummins up the finer thread vs the coarse thread even though it took the same amount of force.



So, we are actually doing less work turning a fine thread one full turn, compared to a course thread.



Let's go full circle and compare this to our inclined plane. In the course case we have to do more work to push our Cummins up the hill, we also have to do more work to turn a coarse thread bolt one full turn than a fine thread. This is telling us the pitch of the threads is controlling the work done in a revolution. However, the force is the same, and so is the final torque value. Pitch determines work, elongation determines force.

I wanted to find real-world testing of this to use as an example, because I can see how most would fall into the trap of believing a fine thread has more clamping force if they didn't really examine the engineering behind it. This forum debated the exact same question: https://www.engineersedge.com/wwwboard/posts/12840.html If you read through, you can see that the poster who did not believe the loads were the same was compelled to conduct a test. What he did was take to equal length 1/2" bolts of the course and fine variety, and center drill a specific depth into the bottom of each screw, and ground a flat on a hardened steel ball. He then used the screws to press the steel ball into a strip of 2024 aluminum. He torqued both screws to the same value and let the ball sit for 1 minute. Oiled threads, same single torque sequence, same condition of threads. He did this for 40 ft-lbs and 60 ft-lbs with two tests per screw. Afterwards, he mic-ed the depth of the indentation left by the ball in every scenario. The result? Fine and coarse threads mic-ed the same in both cases for each trial. Same forces at the same torque. The pitch does not effect torque, and it does not effect clamping load. Controlling friction is the key to using torque values to determine clamping load. And it's because of this, all ultra precision fastener applications do not use torque values! They either measure elongation with an indicator, or rotation in a specified number of degrees.

Fine threads do support higher clamping loads, but only because the tensile stress contact area is larger . If you read literature from unbrako or holo-krome, you'll see fine threads always have a higher torque value to achieve this higher maximum load. That's why ARP uses fine threads on there nuts, they can get more tensile stress contact area out of a fine thread than a course thread, and this means they can support a higher clamping load.
 
1 - 20 of 37 Posts
Top