I've been working on my four wheeler the last couple of weeks and the main problem I have been having is bolts beaking under spec. The manual, says 25 pounds and they break at 15. Most of the bolt are replacement import bolts I ordered off of a website. They all look hardened.

 

WOW!!! I just checked some grade 8 bolts I bought from a True Value hardware store and they are also marked "JH". You're right...not on the list, unless they are the "J" in the illustration. Mine are for the 4 bolts that hold the brake/clutch pedal that mount by the cowl.

And now for a clarificaton on this reprot...IT'S OLD NEWS!!!! I'm not even sure it's still legitimate news for that matter.
I did a search online for defective grade 8 bolts and most everything I found about them was dated a LONG time ago. It's very possible that the list of defective manufacturers has expired or been changed.

Some of the defective bolts also came from Canada. Here's a government bulletin from 1992 that warns about defective bolts:

http://www.eh.doe.gov/docs/bull/bull0082.html

I also found this info which is quite good:
Grade 8 good or bad is kind of like religion - some people think it's fine, other people think it's worse than nails. Most people writing on the internet on this subject are perpetuating hearsay - they haven't really got the knowledge or background to judge what they are judging. I'm in that boat, but I've done a lot of research on the subject. Here's what I found out, after talking to tech reps at companies like Unbrako, SPS, ARP, Brafasco, and suppliers like Coast Fabrication. The first problem is counterfeit bolts. Good bolts cost more to make than poor bolts, so people can make money by counterfeiting bolts. If you buy AN bolts from a reputable supplier, you can also get certificates of authenticity, if you like. That way you know what you're getting. I buy Grade 8 bolts from Brafasco locally, they manufacture they themselves, I have no issues with their quality. I use them for all sorts of things on my cars, like motor mounts, engine trim, headers, air cleaners, bolting the transmission to the engine, and so on. The second problem is the engineering. Lots of bolts on race cars are loaded in shear, double or single. AN specification include a spec for shear strength, Grade 8 bolts have no specification for shear strength. There are rules of thumb to relate tensile strength to shear strength for Grade 8 and other SAE bolts, but AN bolts are made to a spec since AN bolts are designed to be loaded in shear for certain applications. It seems that Grade 8 bolts are designed to be loaded in tension only.

The third problem is the strength. People think that Grade 8 bolts are "brittle". As far as I'm concerned, a bolt that I can turn into a pretzel without cracking sure ain't brittle, and I've bent Brafasco Grade 8 bolts into small circles, to test them. Sure isn't a scientific test, though. Grade 8 bolts are stronger than common AN bolts, which are equivalent in strength to grade 5. Only when you go to a 160,000 PSI NAS or MS bolt or greater do you get to even the equal of a Grade 8 bolt. "Allen" bolts are usually, if from a quality supplier, about 180,000 psi and so are a lot stronger than grade 8 or AN bolts. Another aerospace bolt is the MS 21250 series, at 180,000 PSI they are equivalent to some ARP rod bolts in strength, and I've used them as rod bolts in some applications. When I was looking for these rod bolts, and doing some of this research, I found a 3/8 inch fine thread 1.25 inch long bolt intended for the inside of a Rolls Royce jet engine that cost $300 odd each, and was 320,000 psi tensile. There are a lot of different types of bolts out there!

So the real issue boils down to repeatability. When you put a AN, MS or NAS bolt on your car, you pretty much know, with great certainty, that it will do what you expect it to do, and that it won't fail if you've used it properly. So I use them in situations where I care a great deal about that. But I don't use them in situations where I'm blind-threaded into aluminium - a grade 2 bolt is probably stronger than the threads in the hole. Even some of the suspension bolts in my car are so over-sized that a 7/16 inch nail would do - modern Indy cars use 1/4 inch bolts where I have 7/16 inch. The other thing about AN, NAS and MS bolts, and this is a negative for casual users and a bonus for expert users (which we should all be!) is that they come in very specific lengths in 1/8 inch increments, with only the correct amount of thread to put a nut and washer on. So you need to order the right length rather than grabbing a Grade 8 with a great long thread that fits a wide variety of lengths. The other thing is that they often have a large radius under the bolt head, so that you must use a special washer that's chamfered to clear this radius, or chamfer the part that you're putting it into. If you goof and use a normal washer that interferes with the radius, you've just taken a 180,000psi bolt and put a stress riser in that makes it a failure waiting to happen.

So the only advice that you're likely to get is to use AN and other aerospace bolts for everything - particularly from people who sell those bolts! But the real answer is that while Grade 8 bolts can do most if not all jobs on our vintage cars just fine, the added insurance of using a properly made and tested aerospace bolt is worth the small added cost and hassle, particularly where the bolt is in a place where failure could hurt you.

Dep

 

More of the mentality that stronger is always better. Harder steel is more brittle, so there is a trade-off, but nobody wants to hear that.

It would mean we would actually have to discuss things from a engineering aspect instead of using standard voo-doo.

 

"As far as I'm concerned, a bolt that I can turn into a pretzel without cracking sure ain't brittle..."

Dep

 

DJ and Turtle, as usual are correct in the last two posts....

I would hope the world's bolt manufacturers are holding to a quality level standard for everyone's safety....thing is, with all the new 3rd world nations smelting everything they have to sell, it makes me wonder what is where, and can't trust a damn thing....

gotta LOVE my 40 year collection of mostly old original GM bolts...

I need a 1/2 inch bolt harder/stronger than a teen age dick....gimme one of them olde tyme Pontiac cylinder head bolts, that ought to do the trick....

GENE

 

Hey guys,
I remember a thread not too long ago where we discussed the same thing. I let everyone know that Caterpillar grade 8 bolts have the radius where the head attaches to the bolt, the threads are shaped onto the bolt rather than being cut into it, and the metal is not only hardened but toughened by introducing carbon during the heat treat process. These are the toughest bolts I know of other than aircraft hardware which I used to work on. I have never sheared, broken or even cross-threaded the first Cat bolt since I have been using them during the last 25 years. For the money, they are the very best you can use. If they will hold up on machiney that stresses them far greater than any car could ever hope to, they will far exceed any stress we would ever put on them. Dep is right. Grade eight bolts are not brittle, just stronger and tougher than the others on the market. Use what you want, but for me only grade eight hardware is good enough and for 98% of what I use them for can be found at your local Caterpillar dealer on their shelves and probably cheaper than other suppliers. Their washers, nuts and bolts are all hardened to withstand the stress and hold the torque put on them.
Bernie

 

<sigh> Unfortunately, no local Caterpillar dealer near me

Dep

 

I don't believe it.

I think there are some applicaitons where you don't want grade 8, like the spring bolts. The force on those bolts is not just tension, there is a bending force as well and as the suspension cycles the bending force on the bolt cycles as well.

Would you make a spring out of grade 8 hardened material?

Engineers do things for very good reasons. I'm afraid the mentality of using a grade 8 on everything because its the hardest and highest tensile strength is a fallacy.

 

I agree with you completely turtle, if it's for claming down stuff w/ the bolt in tension, sure use grade 8. If it's for a dynamically laoded bolt, not jsut in tension but also in bending use grade 5, suspension components are a good example.

 

What was the mode of failure? What's the application. Certain grades of bolts are better used for various applications. Grade 8 handles more torque, but is more brittle. For high heat applications, we go to a B7 where we've had the heads pop off on grade 8 bolts. I'm not a metallurgist. Just throwing in my 2 cents.

 

Dep,
Patten Industries has a Caterpillar store close to Wilmette. Phone # 847-548-1177. Just thought you might want to know.
Bernie

 

Thanks Bernie. Still a ways out for me. May use it for crossmember bolts and more critical bolts though. Hope they have a good selection!!


Dep

 

About 15 yars ago there was a buch of counterfit MS grade 5 and 8 bolts. The place I worked did gov. work so we were affected by bulletin. We couldn't use ANY of out grade 5-8 hardware until everything was sorted and checked.

 

All my bolts are so rusted I can no longer see the markings on the heads. Can anyone say with certainty what grade GM used? I'm going to show this thread to my neighbor who has a PHD in metallurgy (sp?) and see what he says. My dad use to be a metalurgist (again sp?) working for North American Aviation, Lockheed and special projects for the Apollo missions. I'll see what he has to say.

 

Jim: Ditto for my bolts. I figured replacing grade ??? rusty bolts with grade 8 new bolts wherever possible would be a GOOD thing.

Dep

 

I either use grade 8 or stainless. it's a lot harder to find real grade 5's. The local Hardware store sells a good selection of grade 8...

There is really no reason to use cheap bolts.

 

correct spelling is metallurgy, i might go into that feild. damn being young can be confusing.

 

The correct spelling for feild is field (see quote above). Sorry for being a smart a$$, I could not pass this up

 

The correct spelling for a$$ is a s s

LOL...watch us all get banned

 

Good discussions ... the only bolt I didn't use that's grade 8
is the rear trailing arm pivot bolt. Mainly, because I bought the
mounting kit.

The only thing I would add is that a grade 8 bolt - into a tapped
aluminum part - is the way to go ... or stainless. Lower grade
bolts corrode easier and seize in the tapped hole. Aluminum
is nasty with low grade steel.