- Engine bolts, lug
nuts, even your oil cap has a specific torque
spec from the factory. Sometimes, you just got no time or you got no patience or
you got no torque wrench. And you just want to
take your own air gun, it down to snug as you can get it. But why is putting a nut on as tight as you can go a bad thing? Why do we even have torque
specs in the first place? And what would happen if we tried to tighten a bolt with
a 13 foot breaker bar? (beep)
This is crazy, man. Well today's video, we are going to show you exactly what
is happening inside a bolt, as it gets over torqued. We are also going to set up an experiment to see if we can replicate our research. So sit back and enjoy as we get down to the nuts and bolts of torques spec. Thanks to bowl for sponsoring
this week's episode of bumper to bumper. Now, if you guys don't know, we do a lot with Omaze because they offer
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Medical Center at UCLA, the same place that saved our dear friend, James Pumphrey's life. The cars that Omaze offers you, the chance to win are sick. How would you like to win a custom Tesla Model X, or maybe even a Dodge Challenger Demon, or maybe even something like this? I know I would, and you could too, just like my buddy Sebastian who won the Corvette Stingray, we helped Omaze give
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chance to win your dream car and support a great
cause at the same time. Head on over to omaze.com/cars and enter now for your chance to win. What are you guys waiting for? Now let's get back to some B2B. Don't worry, the car's not on fire, this is practical effects. Welcome to Donut, baby. (laughs) (beep) Torque spec is the measurement of a force a given nut or bolt is
designed to be used at. It's tight enough to
hold the bolt in place, but not too tight so that it damages anything, including itself. And if we keep on turning
that nut, however, a combination of things
are going to happen. The bolt will break, like we've seen. The metal clamped in between your nut and your bolt, it's going to
buckle, it's going to squish or the bolt will permanently deform. Now the strength of a bolt
is known as tensile strength. And this is the amount of tension the bolt can withstand
without being fractured. Now, if you multiply
this by the surface area that tension is being applied to, you can get the tensile load that you're going to apply to the bolt. So as bolts get more and
more tension put on it, there comes a point called yield point. And this is the amount of tension that it takes to
permanently deform a bolt. Everything below this point,
is called the elastic range and everything above this point, is called the plastic range. Now, when you apply a load to
a bolt in the elastic range, and then take away that load, the material goes back to normal. The molecules that make up
whatever material stretching, they snap back, like elastic pants. Just think of that, that'll
make you remember that. But when you apply a force that
gets into the plastic range and then take off the load once again, the material, it doesn't snap back. Those molecules are permanently broken and the material has undergone, what's called plastic deformation. Now torque spec is often 70
to 95% of this yield point, depending on the application, so it's in that elastic range. After the yield point, the bolt hasn't necessarily failed though. In fact, you may have heard of TTY or torque to yield bolts. Beyond the yield point, the bolt can still be stretched a bit and hold
up to higher tensile load. But eventually, that tensile
strength will plateau and then start to drop off. And that's the point
where you break a bolt. Now imagine a spring,
now you can compress it, just a little bit, or you
can pull it a little bit, but if you pull too far, it's going to permanently deform, and it won't go back to
its nice springy self, even though you didn't actually snap it. That's plastic defamation. Shout out to every 90's kid, who broke a slinky that way. So to show you this, we've set
up a few experiments outside. We're going to use my F150 as a test rig. How I got suckered into
this, I don't know, but let's go to outside Jerry
and see what he's doing. Thanks to inside Jerry. So we're going to put some
of this stuff to the test. We got a rig that we built up
on the back of my F-150, here. We have an extender
coming out of the hitch and through that extender, we have a bolt. And what we're going to do, is we're going to start off by torquing that bolt to 40 foot pounds and work our way up, all
the way to 150 foot pounds. And my buddy here, Joe, he's going to be measuring
bolt length changes as we go up, and over torque this bolt. And then, we're going to
use this big old honker, to see if we can actually get
enough torque to snap an... - [Robotic voiceover] One inch thick - Bolt. We also bought
a 13 foot stainless pole to give us a little bit more leverage to see if we can use
math, to make it happen. And if not, we'll just use these guns. - We're gonna use the math. So what I'm doing now,
is I'm measuring our bolt to see how long it is before
we put it under tension. So that when it stretches,
when we do torque it to spec, we can see how much it's stretched by. - Now we tested several
different types of bolts at varying degrees of torque. And what we found was that our
three and a half inch bolts would stretch about half a millimeter at 120 pound feet of torque. Now, when we undid those bolts, they sprung back to their original length. Now this is a bolt that
is torqued down properly. It's got enough stretch, that the elastic tension
clamps the assembly together, but it still remains true
to its original shape, when the bolt tension is loosened. Now we tried this experiment
again with thinner bolts to see if we could really
show the bolts stretching, but you know, these freaking
guns of mine showed up to do some damage and well,
we rig him, we broke it. (metal clanking) That's called snapping off the bolt, baby. (upbeat music) So we were able to snap
this 1/4 inch bolt, with around 140 foot pounds of torque. So that means to snap
this one inch shank ball, we need around four
times as much, right Joe. - Yeah, maybe. Let's see. - Now this is a one inch shank ball, it's course thread, SAE grade five. So we're going to put about
600 foot pounds of torque using this nice little rig that Joe rigged up, is a breaker bar with a 13
foot stainless steel pole. We're gonna hang sand
bags on the end of it and see if it can snap this. So right now we have 182
foot pounds of torque on this bolt right here. That's factoring in, the weight of this 13
foot stainless steel pole. And the first sand bag Joe is going to put on, is 35 pounds. And we're going to keep
adding bags from there to see what happens. - Alright, let's do it. - Let's go. Do you need a ladder? - A ratcheting wrench won't work for this, so we got to bust out a ladder to get this bar on the breaker bar. - So that's about 600
foot pounds of torque on that bolt right there. So now we're going to add
another 25 pound sandbag. See if it bends it even more. - Six that we're adding,
comes down, so this is 800. And this is about 900 foot pounds. - This stressful. Do you guys really want to keep going. - I've got the hook, Yeah. Alright. This is now getting
like hard for me to move. - Damn, look at that pole bend. I don't want to be anywhere near. - Nope. Hold on. That's good. (laughs) (laughs) This is like the worst game of Jenga. - This is the worst, I
say, we're done, dude. - (laughs).
- This is crazy, man. So we put over a thousand
foot pounds of torque and it didn't shear. So what gives? Did our math fail us? Joe, is it your fault? - You know what? I can't put any more torque on this. - So why did a bolt, four times the size of the little bitty
experiment bolts not break with four times or heck
even seven times the force. Well, let me explain. And when you're buying bolts,
they're measured in diameter. And diameter, that's a one
dimensional measurement and to calculate tensile strength, we got to use a two-dimensional measure. A one inch diameter circle is 16 times the area of a
quarter inch diameter circle. So we would have needed over
2200 pound feet of torque to break that bolt. But the math, it doesn't end there, because the area we need
to use for the calculation, isn't the flat end of the bolt. It's the area of the
surface area of the threads. And that area is partially determined by the thickness of the bolt, but it's also determined by
the thread pitch and depth. So with the larger bolt,
you also have a larger nut and the amount of
threads contacting within that nut increases the surface area of threads touching and
spreading out that force. So even a minor increase in
bolt diameter, thread length, or thread pitch can really change the amount of torque a bolt can take. Because of this, one of the big things that can really become a problem with torquing down
bolts, are contaminants. Now threads, if they're dirty,
if they got grit in them, they got metal shavings
or even surface rust, that can change the amount of
surface area making contact and lower the failure point of the bolt. Also the amount of force needed to break up some of those
contaminants can lead to a false reading on a torque wrench. I'm sure some of you guys
may have heard the term, dry torque and that refers
to the torque applied without lubricant, because
lowering the friction that comes with lubrication
can also throw off torque. So if you're a whiz boy, or you're whiz girl watching this show, you can see by just using a torque wrench, you can get an unreliable measurement. And that's because,
torque is the measurement of turning force applied to a bolt, not the amount of tension
in the bolt itself, but unfortunately there's
no cheap or easy way to measure the actual tension in a bolt. So torque is the only
number we've got to rely on, but because of this, there's
another technique out there that makes torquing down fasteners to perfect spec, super duper easy. It's called the torque
and angle technique, and here is how it works. Instead of just the
measurement in pound feet. You have a measurement and an angle. So if your torque spec is
30 pound feet at 90 degrees, you torque your bolt
down to 30 pound feet, and then you'd give it a quarter turn. Why are quarter term? Well, every 360 degrees
of rotation of the bolt, the nut moves down the
thread by fixed amount. This is called the thread pitch. So when you start off with a lower torque value, snug
torque, every degree of rotation after this will be used
to stretch that bolt. Because no matter what, that
quarter turn is going to move that bolt down the same amount
of thread every single time. So this pretty much eliminates the fact that variations in friction have on the torquing process compared to when you're just using
a torque value on its own. And if you want to see
bolts, get expertly torqued by Mr. Zack Joe, go check
out our series, Money Pit. If you want to see some
behind the scenes footage of all the stuff we can't
include in this episode, because we're very serious in B2B, but sometimes we do a lot of goofy things that you don't get to see. Go hit that join button down there and be a part of the Donut underground. Follow me on Instagram, @jeremiahburton. Follow us on Donut, @donutmedia. Until next week, bye for now.
