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Grade 5 vs. grade 8-shear?

 
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cutlass389
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PostPosted: Tue Feb 03, 2009 12:13 am    Post subject: Grade 5 vs. grade 8-shear? Reply with quote

I thought I would avail myself of the collective braintrust here as mine is mostly fermenting Jello(registered trademark). I seem to remember reading somewhere that in a single shear application, a grade 5 bolt is actually better than a grade 8. Is this accurate?
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af2
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PostPosted: Tue Feb 03, 2009 12:21 am    Post subject: Reply with quote

Grade 5 will bend before shear, grade 8 will shear and not bend.
It has to do with what you are using it for. Suspension etc use grade 5.
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yourconfused
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PostPosted: Tue Feb 03, 2009 1:45 am    Post subject: Reply with quote

af2 wrote:
Grade 5 will bend before shear, grade 8 will shear and not bend.
It has to do with what you are using it for. Suspension etc use grade 5.


That is what I have always been told by fastener companies.
Take a cheap drill bit that is soft like a grade 5 and it will bend before breaking, also get dull quick. Take a quality drill bit that is harder, stays sharp longer, and it will shatter when twisted.
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Big Dave
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PostPosted: Tue Feb 03, 2009 2:21 am    Post subject: Reply with quote

You use a grade eight to resist shear (such as clutches). The grade eight also has a higher tensile yield (stronger as it is made of an alloy) as opposed to the mild steel grade five that has only been case hardened to get it above its normal (Chinese quality) grade three.

A grade eight is better for most applications but not all. It's increased strength also makes it more brittle as mentioned. If you want a bolt that is tuff (bends but won't break if within it's rated application) use 403-404 stainless.

Big Dave
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yknot
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PostPosted: Sun Jul 12, 2009 7:20 pm    Post subject: Reply with quote

You cannot talk about Sheer unless you qualify weather it is a bolt in single or double sheer position. Grade 5 is considered to be the absolute minimum for automotive fasteners. Grade 8, is an up-grade 99% of the time, in terms of strength and fastener tension retention. I cannot think of one, not one area where it would be BAD or un-wise to replace a grade 5 bolt with a grade 8 equivalent. We specialize in replacement hardware for Modular engines, and typically sell grade 10 or better (DIN12.9) fasteners. Even on suspension pieces, if the mounting is fabricated correctly, and a double sheer arrangement is employed, Grade 8 or higher bolts are the way to go. Bolts have many aspects to them beside sheer alone, and you can not consider one without regarding the others. Most NHRA top classes have their roll over protective structures constructed from chrome-molly tubing, while all NASCAR roll over structures are 1020 Mild Steel? Does one work better than the other? They both serve to protect the driver from an accident at very high speeds, and when there is a crash, I have rarely seen a roll cage fail. It's just plain goofy to think that your Grade 5 bolt will outlast or protect better then a Grade 8 or higher, or that the Grade 8 will simply crack in use. It don't work like that. All the top race teams use grade 8 or higher bolts for the entire assembly of the vehicle, unless a place calls for a higher value.
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clay
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PostPosted: Sun Jul 12, 2009 9:01 pm    Post subject: Reply with quote

About the only time I have seen a harder bolt (12.9 CHC) fail over a softer bolt (8.Cool is when the fastener gets loose and gets hammered really hard with impact. Another use is if we use the bolt for a pin. I have actually seen this at work, however I will agree and state that it results from either too small of a fastener, poor engineering of brackets, etc., or just plain lax installation. I think a properly designed and installed grade 8 will always be the better, stonger setup. Clay
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Knarley Darley
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PostPosted: Mon Jul 13, 2009 2:01 am    Post subject: Reply with quote

So you are telling me the aluminum bolts holding the flywheel on to my pro stock engine are not safe? I thought they would be stronger because of their weight????? I torqued them to 10 inch pounds. Are they going to come loose?
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10sec.et
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PostPosted: Mon Jul 13, 2009 11:02 pm    Post subject: Reply with quote

Knarley Darley wrote:
So you are telling me the aluminum bolts holding the flywheel on to my pro stock engine are not safe? I thought they would be stronger because of their weight????? I torqued them to 10 inch pounds. Are they going to come loose?


did you use red, blue, or green loctite ? Poke

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It seems we can look at our magical Balls and come up with a fix?

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Knarley Darley
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PostPosted: Wed Jul 15, 2009 4:24 pm    Post subject: Reply with quote

I used the impact. I tightened until it got easy, and backed off a half turn.
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10sec.et
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PostPosted: Wed Jul 15, 2009 7:07 pm    Post subject: Reply with quote

Knarley Darley wrote:
I used the impact. I tightened until it got easy, and backed off a half turn.


i was worried about using the impact but since you backed off 1/2 turn, it should be fine. can i come stand at the starting line and watch the car launch ?

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af2
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PostPosted: Wed Jul 15, 2009 7:40 pm    Post subject: Reply with quote

yknot wrote:
You cannot talk about Sheer unless you qualify weather it is a bolt in single or double sheer position. Grade 5 is considered to be the absolute minimum for automotive fasteners. Grade 8, is an up-grade 99% of the time, in terms of strength and fastener tension retention. I cannot think of one, not one area where it would be BAD or un-wise to replace a grade 5 bolt with a grade 8 equivalent. We specialize in replacement hardware for Modular engines, and typically sell grade 10 or better (DIN12.9) fasteners. Even on suspension pieces, if the mounting is fabricated correctly, and a double sheer arrangement is employed, Grade 8 or higher bolts are the way to go. Bolts have many aspects to them beside sheer alone, and you can not consider one without regarding the others. Most NHRA top classes have their roll over protective structures constructed from chrome-molly tubing, while all NASCAR roll over structures are 1020 Mild Steel? Does one work better than the other? They both serve to protect the driver from an accident at very high speeds, and when there is a crash, I have rarely seen a roll cage fail. It's just plain goofy to think that your Grade 5 bolt will outlast or protect better then a Grade 8 or higher, or that the Grade 8 will simply crack in use. It don't work like that. All the top race teams use grade 8 or higher bolts for the entire assembly of the vehicle, unless a place calls for a higher value.


Apparantly you didn't understand my quote! Laughing
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clay
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PostPosted: Wed Jul 15, 2009 9:00 pm    Post subject: Reply with quote

Quote:
I used the impact. I tightened until it got easy, and backed off a half turn.

Well crap, that's where my problem is - I always torqued it until it snaps then back off 1/2 turn Very Happy . Clay

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Knarley Darley
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PostPosted: Thu Jul 16, 2009 2:10 am    Post subject: Reply with quote

Sorry. didnt mean to hijack the thread. You guys just crack me up.
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Big Dave
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PostPosted: Thu Jul 16, 2009 9:44 am    Post subject: Reply with quote

Knarley Darley wrote:
So you are telling me the aluminum bolts holding the flywheel on to my pro stock engine are not safe? I thought they would be stronger because of their weight????? I torqued them to 10 inch pounds. Are they going to come loose?


Depends upon the alloy chosen and the heat treatment they received. There exist aluminum fasteners that will meet a grade eight tensile and shear test but I wouldn't use them because aluminum work hardens and steel (of the proper size and temperance) for a given application will not.

Big Dave
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