Grade 8 vs Grade 5

http://www.rockcrawler.com/techreports/fasteners/index.asp

Good article that explains things very well.

 

GREAT article...thanks for posting ....

 

I have touted this for years, some people are just hard headed.

 

Excellent read. Makes me want to go re-torque all my bolts, after I make sure they're grade 8 that is.

 

the great bolt debate. as with anything, always think of the design as a whole.

 

And if you find that page interesting, you may want to look into Carroll Smith's "Nuts, Bolts, Fasteners and Plumbing Handbook". A lot to do with race cars, but does give some great info on the metallurgy and the hows and whys of bolts. (Ever tap extra threads into a bolt? You'll wish you hadn't after you read this book....) Bottom line...If you ever need to trust your well-being to a bolt, READ THIS BOOK FIRST!

 

Counterpoint time!

Not to start a big ol' debate, but sometimes the strongest fasteners aren't necessisarily the best choice for the application:

http://www.utterpower.com/engineer.htm

 

Agree w/ everything but this. I was always taught to use anti-sieze on the threads. Every mechanical school I took in the Navy as well as Power Plant training as a civilian expressed this in regards to obtaining proper torque on a fastener (especially important on SS which is subject to galling w/o it). IMO not only is this important to obtain proper torque, it also prevents corrosion.:v6:

 

I agree with you on this.

 

Re: Counterpoint time!

Sometimes not exceeding rated capacity is the best choice... the weakest link is going to fail first, yes. Change the weakest link from the bolt to the component and then subject it to a lot of abuse... Just reading the story I have to suspect the condition of the components to begin with after that kind of use.

From an engineers standpoint, relying on old "soft, weak, and stretchy" bolts to keep your machine running is bad bad bad bad BAD. Sure in this isolated case where it's just an old tractor, who cares... but in any application involving potential loss of limb and life, the ONLY choice is the CORRECT fasteners (and yes, sometimes grade 5 IS good enough), which are tightened properly, and factors of safety... meaning you run things far BELOW their actual capacity, not ABOVE...

Sorry, but from where I sit this "Backyard engineer" shouldn't be using the E word... If you readily admit to wildly abusing the equipment, there's only one proper place for blame when it breaks.

 

:iagree: And on top of it, there's no telling how many cracks already existed in the cast iron parts prior to the rebuild. I wouldn't throw blame at Grade 8 bolts when the rest of the item suffered severe punishment all that time.

Grade 5 being more "stretchy"? R) R) R) R) OK, (wipes tears from eyes) I'll give you that "technically" that is uh, accurate. But in reality, I seriously doubt that less "stretchy" bolts had much, if anything, to do with that guys machine breaking in half.....He makes is sound like it was held together with bungee cords and rubber bands. Sheesh.

 

To add to this, GOOD drawings and engineering will specify whether or not to use anti-seize when bolts have to be torqued to a certain spec. The anti-seize will allow slippage and the bolt will be tighter that if it were torqued dry.

Ask the guys on the 2A page - the ones that use anti-seize on their head bolts and torque them to factory specs have numerous time snapped them off. Those doing it dry have no problems. So, the ones that have learned this and still want to use A-S on the bolts just torque them to about 5-10 ft lbs less than the spec.

 

It seems to me in our part of the world, all this is a moot point anyhow, because it seems like all I can find anymore is Chinese made junk that has no grade marks on it and if there were, it would be grade "cr*p" that I think is made out of pot metal. Sorry but this hot subject with me. The other day I went to every store in town (small town, only 5 stores carry bolts), and every bolt I could find was Chinese grade cr*p with no marking on the bolt. If you have ever used any of these bolts, you know what I mean

 

when it come to sometime like headbolts, well anything that has stated torque specs (i.e. ft- lbs, N-m, blah-blah, dry, wet, cold , hot) should be followed. moreover, on a very few engines "can" reuse headbolts according to the original builders. maybe, this had something to do with it. maybe not. i'm just glad its not me with broken headbolts.R)

 

Did they use any engineering when they made the 2As? R)

 

So, speaking of headbolts....where can a guy get a good-quality set of new head bolts for an F-head?

 

(ears perk up) ggood question

 

Wondered about this when I replaced the hub bolts in Lincoln. Some said I should use grade 5 because they had better shear strength than grade 8. I'm glad I used the grade 8.

Then again, some said I should use grade 5 to create a weak point so that if something broke it'd be the bolts and not something expensive.

I chose the grade 8 cause I din't want anything to break.

 

If they were used, it wouldn't surprise me. Bolts "hold" things by virtue of stretching. There's a tiny amount of elasticity in a bolt, and by tightening to a given torque, you are avoiding over stretching the bolt. (The whole point of torquing to a given point is to place the bolt stretch at such a point that the cycles are nearly endless, but still hold the item tightly.) Tighten in exess than the "correct" torque, and you shorten the bolt's life. Taking into account that there are only so many cycles of stretching a bolt can go through before it fails at X torque, and that a head bolt will stretch with the engine heating up and cooling off, and then re-using it and torquing with anti-sieze (thus causing more torque than specified), I could see how you can take the bolt beyond it's failure point.

I STRONLY recommend the Carroll Smith book "Nuts Bolts and Fasteners", see it HERE.
It WILL break a lot of misconceptions on how bolts work, and you will rethink a lot of how you use them.