GRADE 5 or GRADE 8...that is the question

Thanks, I will...and do. I respect the the wisdom from the SoCal book and respect the advice from the folks on here as well. I can't imagine stretching a 5 or 8 bolt to failure and as far as shearing a bolt, if all attachment points are built logically and everything is tight (to spec), you should be golden.

....great thread! HAHAhahaaaaa get it?! Thread?!

 

My two cents on bending vs shearing -- when I was growing up on a farm dad always used softer steel hitch pins instead of the hardened ones because they would deform instead of shear.

However, that was in a loose connection that was banging back and forth.

Very few bolts, when properly tightened, will experience any lateral motion so it seems the entire debate is moot.

But each connection needs to be looked at and the best bolt used.

If you want to get really confused consider places where a larger diameter Grade 5 could be used or Grade 8 one size smaller with a bushing.

My thought is either one will work in many applications but we should err on the side of caution.

And look at something that's been running for a while and see if anything shows signs of wear/bending.

As to the "streaching" of the bolts during tightening -- it stops well short of the "deformation" point and increases the pressure holding the pieces together.

 

If the suspension is all properly designed double sheer joints, how are those grade eight bolts going to bend? Mounting grade eight in double sheer makes them awful tough. Stretch would not be a likely load on the bolt in such a design. Clamping load would be a product of joint design, bolt diameter, (for a given grade) and torque value, I would think.

Craig

 

The problem with grade 8 is catastropic failure. When they fail it is sudden and complete. Some things require g 8 like flywheel bolts. Suspension works better with g 5. Use what oem car maker applications use. Ford,Gm,etc are not usualy a bad source for good applications. G 8 sure wont work on ul aircraft landing gear legs.Been there d.........

 

So how do you know you're getting genuine Grade 5's? Don't think for a minute they aren't out there too. We've run into it several times at work. We buy in large quan***ies and require certificates of conformance and chemical/physical ****ysis reports with all hardware and we've still had a few boxes of counterfeit Grade 5 and grade 8 bolts plus Gr 8.8 and 10.9 in Metric slipped in.

If you have doubts about the hardware you get at the local Lowes or where ever buy a couple extra bolts and nuts, measure the overall length of the bolt, clamp the nut in a vice and with a short piece of tubing between the head of the bolt and the nut start torquing it to the maximum torque for that size and grade fastener. When you reach maximum torque measure the overall length again, it shouldn't be apprecaibly longer. Then start torquing it in 5 FtLb increments until it fails or you run out of torque wrench. It should go beyond the torque upper limit before failing.


I use Grade 5 on intakes, accessory brackets, etc. but Grade 8 for anything safety related and in some apps Grade 12 aircraft hardware if I can get my grubby little mits on it.

 

It's very hard to detect the fakes. I rely on getting them from known vendors. The fakes look identical these days.

If you do a search on Google of "counterfeit grade 8 bolts" you'll see a whole lot of talk about how much of a problem it is.

 

Yep.. they counterfeit the 5's too... I get my 8's from a reliable supplier for use on the important stuff. I keep a bin of them handy. Occasionally for non structural stuff I'll use bolts that I can't verify the chain.

 

Jimmy, do you belive everything you read?

Bad information is worse than no information and using wives tales to build engineering principles from is horrid. Take it from someone who has been in the business a while and has seen the "bending" before breaking ****. IT IS A LIE! You have been missinformed or lied to to belive that a Grade 8 bolt will not bend but will snap.


I have a box full of 5/8" grade 8 bolts that have bent from our axle dropping fixture that have taken nearly 40 Tons of shear load. NEVER has one sheared or failed, only bent.

I have seen Grade5 hardware fail and not bend on suspension atttachement point from road shock like a pot hole or buckle in the road. I have seen plenty of Grade 5 hardware stretch prematurely under the stress tension and load of the suspension directly because it is under rated for the application.

OEM's use Grade 8 or higher on every suspension part I can think of regardless of manufacturer. Besides, we already coverd this stuff not that long ago.

http://www.jalopyjournal.com/forum/showthread.php?t=256926

 

I was just gonna mention fakes...I think for *most* people, maybe not the people on the HAMB but for myself I guess...I'm buying fake grade 8's anyway, so it doesn't matter if I buy the fake 5's or 8's, it's all bogus and a **** shoot IMHO.

In Carroll Smith's 'nuts bolts and fasteners book' which is from the 90s I believe, he talks about fakes. As I recall he said if you don't buy from an American manufacturer(from a bolt store), you can bet it's a fake. Once the chinese figured out there was more money in putting those hashmarks on a bolt, it was all over. If They'll fake cancer medicine, they'll fake anything, and that sure seems to be where most of our products/steel comes from lately.

Glad this thread came up. I was thinking I need to get some more bolts from the bolt guy at the swap meet. What I really need to do is toss all my old ones out or give them away and buy some real ones at a fastener store. That's about the best I can do to insure quality at this time.

EDIT: Just took a look at that other thread about Fatman recommending grade 5 on suspension. Gave me a chuckle. Based on my experience with them and what I've read of other peoples, I wouldn't believe them if they told me what time it was. Sure glad the fella asked that question!!

 

Quoting myself from the other thread:

<HR style="COLOR: #999999" SIZE=1><!-- / icon and ***le --><!-- message -->
http://www.engineershandbook.com/Tables/boltgrades.htm

And annother fantastic article, this one explained in detail.

http://www.rockcrawler.com/techrepor...ners/index.asp

Quoted for emphasis:

Quote:
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD cl***=alt2 style="BORDER-RIGHT: 1px inset; BORDER-TOP: 1px inset; BORDER-LEFT: 1px inset; BORDER-BOTTOM: 1px inset">Again, you can see that the grade 8 will support over 1000 lbs more or a 1/2-ton more. But there’s something more important to note. The grade 5 fastener has already reached its ultimate load and FAILED BEFORE the grade 8 starts to yield or stretch. Therefore, the argument that you should not use grade 8’s because they are more brittle than grade 5’s is not a true statement in most applications.

</TD></TR></TBODY></TABLE>

 

Fortunately there are still some quality manufacturers of hardware out there. Don't wish to hijack here, it's a good discussion.
The design element that I've seen crop up, is the tendency to "swiss cheese" the mount or joint when fabricating, and then use grade 8's which will remain torqued down tight, though the flange or bracket has failed. I always try to keep the "web" between adjacent bolt holes sufficient to match the strength of the fasteners. In rod construction we have singular peak loads, and often lesser fatigue loads, to base a build upon. There was mentioned somewhere a rule of thumb about fatigue, and some of our design guys can weigh in here. Something re: 1/10th of a permanently deforming load, would if done often enough-fatigue (concrete roadway joints come to mind), be a possible mode of failure? Steel, in strength hardening as it deforms does us a bigtime favor.

 

This is not from any scientific writings or tests or anything, but I have always done that too.
I use Grade 8 on things where ultimate strength matters most, and prefer to use the more "elastic" grade 5 on things like intake bolts etc where a little bit of "stretch" could help keep a gasket clamped in place better.

The way I look at it is that with certain parts heating up and cooling off, heat, cool, heat, cool, the mating parts are always squirming around a little bit, and that a fastener that can follow it with a little forgiveness will protect the gasket seal better than a super stiff fastener that won't follow along.

Here is a picture of what I do with my manifolds.

I select bolts with a little elasticity built in, I use longer bolts than most others use (a long spring has a more consistant spring rate over its range of travel (stretch) than a short one that can't give anything), and take advantage of their ability to "go with the flow" when the parts are changing sizes and dimensions due to the severe temperature changes.

View attachment 456761

This is my crude but practical way of insuring there will be no intake leaks as the parts swell and shrink at different rates.
Simply use a longer, stretchy, bolt and a hold-down clamp that fits loosely around the bolt.

In this one I am using a valve spring retainer turned upside down, as a "clamp" that can rock ever so slightly as the very hot heat riser p***age on the right swells larger than the cooler intake p***age on the left.
As the cooler intake p***age on the left slowly picks up engine heat and almost catches up (temperature-wise AND size-wise) to the now cooling-down-a-bit heat riser p***age, the spring retainer and the long stretchy bolt will have enough elasticity and give to keep the clamping-tension on the gasket pretty much evenly throughout the endless stretching and squirming and shrinking cycles.

I NEVER have any intake leaking problems when I do it this way, even when playing with turbos up to 24 lbs boost so far.
The friends and others at the track that I see having intake sealing problems seem to always be using shorter bolts with no stretch or forgiveness to them.

That is especially true if you use an aluminum intake. Picture the aluminum swelling at a much bigger rate than the iron. What happens when the part you bolted in place gets bigger than the space allowed by the hard-tightened, non-elastic, super-tough grade 8 bolt?
That puts a tremendous pull on a short bolt with no give. What happens? The threads in the fragile cast iron are pulled way beyond the torque and clamping forces that you USED to have. Then the gasket gets crushed beyond its ability to crush-and-rebound even if you were careful not to overtighten.
When the aluminum (or iron) cools and shrinks, you now have a space under the bolt head that is no longer filled quite as tightly anymore. After a large number of those cycles you can easily have crushed gaskets, loose gaskets, loose parts, internally damaged cast iron threads that may not show up for some time, or at the very least, mating parts that can break the gasket-seal by squirming around.

Yes, I believe there are quite a few places where you would prefer a somewhat stretchy bolt than can go with the flow.

 

Why didn't my pic appear?
I will try again to get the picture to show here....




This is the method I use. A longer bolt, a bolt with a little "give", a clamp that can wiggle or rock a little bit as needed (loose fitting valve spring retainer upside down), and do-it-yourself- home-cut intake gaskets glued to the ported head but not glued to the manifold.

I never have leaks.

If you are worried about pretty looks, I am sure it would be easy to use much more stylish items to do the same job. A taller bolt and chromed tube? (must be a strong thickwall tube)


Or maybe some items under the bolt heads that look like fittings for some wild plumbing that would leave people scratching their heads?

Hey, that would be cool if you didn't want any compe***ors to find out what you are really doing to go fast.

Man, now I wish we would have done that on the race car to really freak people out and throw them off our tail.

 

most modern cars use grade 5 bolts for the suspension.

the thinking is that in an accident situation, the grade 5's will bend but not shear or snap, allowing the suspension to stay together, albeit bent or mangled.
grade 8's will snap easier allowing the suspension to come apart and greatly improving the chances of some sort of violent reaction.

i was always taught to use grade 5 for suspension.

 

Really, you can't be serious. Did you even bother to read this?

Show me proof that new cars use Grade 5 bolts then I might belive your statement.

 

All you have to do is a simple www.google.com search to find your answers.

http://www.google.com/search?hl=en&...d=1&q=shear+yield+strength+bolt+grade&spell=1

This taken from www.pirate4x4.com and more specifically http://www.pirate4x4.com/forum/archive/index.php/t-40342.html

Again for emphasis: A Grade 5 bolt will bend and FAIL before a Grade 8 bolt will bend!

 

I needed a good laugh this morning. Thanks for providing me with the material to laugh about! Ignorance FTMFL!

 

Wow...this thread is promulgating as much "traditional hot rod" mythology as ANY one of the similar threads about driveline phasing or Ackerman.

"The thinking is..."...."What I have always heard...."...WTF!? Facts, boys...all of which are readily available from myriad Internet sites or the excellent books on the subject, already referenced in this thread.

There is a prevailing MYTH that Grade 8 bolts "shatter" or catastrophically shear in a situation where a Grade 5 would simply bend. THIS IS A FUNDAMENTALLY INACCURATE STATEMENT. The statement refers to what many percieve as "brittleness" in a bolt. People percive Grade 8 bolts are more brittle because they are harder.

"Brittleness in bolts is defined as failure at stresses apparently below the strength of the bolt material with little or no evidence of plastic deformation. Typically, fasteners are not brittle below 180 ksi ultimate tensile strength. Grade 5&#8217;s have an ultimate tensile strength of 120 ksi and a grade 8 fastener has an ultimate tensile strength of 150 ksi."

The point THERE is that if a Grade 8 bolt were to reveal the attribute of "brittleness", it would only do it in a load environment 20&#37; GREATER than it's tensile strength yield point.

And hardness.?..

"Toughness is an important feature of a fastener. It is the opposite of brittleness and gives you an idea of how it will handle abuse without being damaged and eventually weakening the fastener or can cause fatigue to appear much earlier than normal. One way to &#8220;measure&#8221; toughness is by looking at the hardness rating of a fastener. The higher the number (Brinell, Rockwell &#8230 the harder the material is and the tougher it is to damage. According to Marks&#8217; Standard Handbook for Mechanical Engineers, Grade 5&#8217;s typically have a core Rockwell hardness of C25-C34 whereas a grade 8 typically has a core Rockwell hardness of C33-C39. Based on this, grade 8&#8217;s are tougher than grade 5&#8217;s."

Simply put, a Grade 8 bolt will outperform a Grade 5 in all situations. Furthermore, a Grade 8 bolt will yield in tension and shear just like a Grade 5, (experience plastic deformation) only at relatively higher loads...and finally, a Grade 5 will yield to failure BEFORE a Grade 8 deforms!

This is not opinion, sports fans. This is supported engineering data. The notion the "Grade 8's will snap easier" is not only counterintuitive, it's not supported by the laws of metallurgy.

SoCal and Fatman justify the use of Grade 5 bolts because they know that STUPID people will believe it. Seriously. Re-read everything El Polacko just wrote. And GET OVER disseminating false information or mythology.

 

"....
Simply put, a Grade 8 bolt will outperform a Grade 5 in all situations..... "

"all situations"?

You are talking in terms of total strength, not stretch, not forgiveness.

What does "outperform" mean?
They are talking brute strength ONLY.

Thats like saying "the stiffest spring will be best in all situations"
Not true when you DO want some "give".

Go ahead, take your short stout grade 8 bolt and attach a large aluminum piece to your soft cast iron threads.
Heat that aluminum to swell it up a lot to really put a stretch on that bolt.
What damage have you done to your soft cast iron threads with your super grade 8 pull?? Swelling aluminum puts one hell of a pull on even lightly torqued bolts.

What you NEED in that case is a more elastic bolt (more length plus less heat treat hardness) that will allow the aluminum to swell and then shrink, and still keep a reasonable tension to hold the part in place. Grade 8 will not give you that. It will greatly "over-pull" when the part swells up.

There are times when you do NOT want a "no-give, me-tough-guy" bolt that wants to rip the soft threads out of your cast iron every time a piece of aluminum or a super heated part swellls up big due to heat.

Don't be one of those guys who needs 7/8 inch bolts and 80 ft lbs of torque to bolt on an oil pan.

By the way, I use grade 8 on most things that matter, but I won't use it on EVERYTHING.

 

I base my bolt grade usage on the application. If a grade 5 bolt has more than enough strength - thats what I use. I usually use 2x safety factor and have never had an issue. If the grade 5 bolt doesn't meet my self impossed 2x safety factor...then I use the appropriate grade.

When you get to specialized fasteners however - such as stretch to yield and those that are required to allow for thermal changes in size...you really do need someone who knows what they are doing.

 

grade 8 bolts have a higher tensile strength but they're more brittle and will snap before they bends. the lower grade bolts are able to flex with vibration where the grade 8 bolts are not. this is the exception to the rule, in most cases a grade 8 will be superior to a lower grade.
<!-- / message --><!-- sig -->

 

nissan uses grade 5 for suspension on their cars.

 

Bolts stretch depends upon a number of variables...material, diameter, thread pitch, and length.

The appropriate torque specification for a bolt is consistent with it's stretch qualities...the torque results in stretching the bolt the required amount, which imparts the clamping force. That is WHY there are torque specifications...to INDUCE the appropriate bolt stretch to ENSURE adequate clamping force.

So, that being true...and it is...how far does a given bolt stretch? Well, the math is a bit complex:

Bolt stretching according Hook's Law can be expressed as

dl = F L / E A (1)

where

dl = change in length of bolt (inches, mm)

F = applied tensile load (lb, kN)

L = effective length of bolt where tensile strength is applied (inches, mm)

E = Young's Modulus of Elasticity (psi, N/mm2)

A = tensile stress area of bolt (square inches, mm2)

Tensile stress area can be expressed as

A = 0.7854 (d - 0.9743/n)2 (2)

where

d = nominal diameter of bolt (inches, mm)

n = number of threads per inch (pitch)

Example - Bolt Stretching
stud diameter : 7/8 inches
thread pitch : 9
Young's Modulus : 30 106 psi
design bolt load : 10000 lb
effective length : 5 inches
Tensile stress area can be calculated as

A = 0.7854 (7/8 - 0.9743/9)2

= 0.46 (in2)

Change in length of bolt can be calculated as

dl = 10000 (lb) 5 (in) / (30 106 (psi) 0.46 (in2))

= 0.0036 (inches)

And yes, this example is based on a 7/8" bolt, as opposed to a typical 3/8" manifold bolt...but you can see that the 7/8" bolt only stretched 36 TEN THOUSANDTHS...

How about a more common 3/8" bolt, like a rod bolt? What does ARP say about rod bolt stretch?

Well, you're looking at about .0057" stretch....thats 57 TEN THOUSANDTHS, at 25 lbs of torque.

Here is my point. Your premise that, somehow, your longer softer bolt has sufficient "stretch" in it to compensate for the the various material expansion rates of a given engine is a myth. "Forgiveness" is, again, counterintuitive.

Specifically, what OEM or aftermarket fastener, exhaust header, cylinder head, engine block, or intake manifold manufacturer specifies using over-long fasteners coupled with used valve spring retainers and bits of tubing to connect their components?

More to the point, what OEM or aftermarket fastener, exhaust header, cylinder head, engine block, or intake manifold manufacturer does NOT provide a SPECIFIC torque for their components?

I can think of only four places, on a reciprocating normally aspirated OR forced induction engine where such an occurence exists: Supercharger-to-blowermanifold studs (typically aluminum, to facilitate "lifting" the blower in the event of a backfire), spring-over-bolt fasteners on blower manifold pop-off plates, spring-over-bolt toggle clamps on flexible forced induction (turbo or centrifugal blower) discharge or intake tubing).

You are fooling yourself with the idea that, somehow, your BOLT is like...a rubber band. All you've accomplished is to pile enough stuff ON the bolt to create a series of mechanical intersections that preclude you from using the fastener as it was intended.

 

/Story

 

A long bolt will indeed maintain a much more even clamping force over a certain amount of "stretch and shrink" than a short bolt will.

To easily illustrate, lets show an exaggerated situation so it will be easy to see...

A 1 inch long bolt versus a 20 foot long bolt. We are using it under tension, not shear.

Tighten the 1 inch long bolt to get 30 thousandths stretch.
That bolt went past it's failure point. Failed.

Tighten the 20 ft long bolt to get a 30 thousandth stretch.
The long bolt easily absorbs this without problem.
In fact a 25 thousandths stretch or a 40 thousandths stretch will still give you a similar bolt clamping-tension on the 20 foot long bolt.

On the short bolt, a couple thousandths stretch could give you strong tension, and a few more thousandths of pull could give you terrific tension that could strip threads in your cast iron or aluminum threads.
No room for a bolted-on part to swell up with heat, or the short bolt will pull on the threads way too much.
Then when the swelled up part cools and shrinks, it suddenly is not tight enough. Tighten it when cold and it is too tight when hot.

OK, so the 20 ft bolt is too long.
Take a 2-1/2 inch long bolt instead, and compare to the 1 inch long bolt.
The longer bolt can tolerate much more swelling and shrinking of an aluminum part and still maintain a decent, relatively even, clamping force than the shorter 1 inch bolt ever could.

If you change the thickness dimension of an aluminum part being held by a short 1 inch long bolt (heating and cooling cycles), the 1 inch bolt will go from too loose, to too tight, to too loose, too tight, over and over again.
A long bolt can indeed absorb that without problem.

Remember this illustration is about tension, stretch, clamping, and ability to keep a sealing surface sealed, not about shear strength.

 

Dang Steve, I absolutely do NOT believe everything I read. Relax, Holmes. That's why I put this up. I was hoping someone could clarify the matter for me. I'm no expert like you are and I respect your knowledge as well as others on here. The other threads only added confusion (at least to me). Long story short, I'm using grade 8s for suspension stuff, but was wanting to hear of actual experiences and yes, opinions.
Go ahead Steve, say it, "stick to drawing cars"! ha

 

Whoa Jimmy, I'm not taking you out to the woodshed just yet...


I am here to firmly state and educate to the positive using sources that anyone can find and are scientifically backed by solid engineering, not he****ay. I'ts when dinks like Tredboy start making ignorant statements like this that I get a bit wound up.

This is false information and it needs to be killed. There is no shred of truth to this statment and comes from someone who aparently cannot read or is not capable of research.

PROOF? Well yes I have some




These are 5/8" Grade 8 bolts that have seen over 80,000 pounds of shear load on our axle dropping fixture. Never has one sheared, shattered or snapped. Only bent.

Oh, and Nissan can't possibly use Grade 5 because they use metric bolts which are carry an ISO rating which uses different terms. In fact almost ALL auto manufacturers are now using ISO Metric standards for all ch***is and drivetrain ***emblies.

 

LOL

 

You and me in the woodshed? Remember last time and how all the people talked?

 

That is exactly the reason that I never spec. stainless for anything beyond cosmetic/no load applications. Honestly, it's tough to use a bolt correctly and put it in bending. For example, if you bolt a sprocket to a hub the bolt is still in tension. The bolt is pulling the sprocket to the hub and the friction of the hub against the sprocket is actually resisting the load before the bolt can bend.