grades of bolts

Im currently redesigning a lower alternator bracket ,Im using grade 5 bolts ,Only reason is that they are threaded all the way up. Anybody else use grade 5 for the same application . Or anybody have any issues with grade 5 breaking ..... I know this thread is lame........................

 

For an alternator, grade-5 should be just fine.

 

Grade 5 is good for that.

 

I am actually running stainless ones with no troubles. I don't think you would have trouble with G5 on this, I may be wrong, seek other opinions as well.

 

Grade 5 is fine for everything on the car except spring center and U bolts.
Keep in mind most stainless bolts are only grade 2, unless otherwise specified. Chrome bolts are a better choice as most are grade 5.

 

Hard to say without a picture of your design. The thing about needing fully threaded bolts makes me wonder.

 

It's a good rule of thumb that anything suspension related should be Grade 8, minimum.

 

Cool guys that what I was thinking ,The design is very simple.On the lower alternator mount ,There are 2 holes on the block where the alternator mounts ,Lower one actually holds the alternator and hole above it holds the top of the bracket ,Im putting a flat 1/4 plate to span both holes up against the block and weld a sleeve to the top of the Mr .Roadster bracket . Ill post a pic later ,Im not that far yet , Tonight I will be .Im a firm believer in grade 8 on everything and Didnt want to run the die down ,chasing my own threads ,Bought grade 5 instead ,Gonna be using it as a stud.

 

Is it the main mtg bolt and is it in single or double shear?

 

Many of the dirt track stock cars use grade 5 for suspension. They say they can take a hit and bend, where a Grade 8 would snap off. something to think about.


Ago

 

Here's a lame answer............grade 5 are fine for what you're doing

 

I agree with Ago, my experience has been stainless and gr 8 will snap, gr 5 will bend before breaking. When sorting my bolt stash(es) I s**** the no-grade stuff. peace

 

I agree, gr8 provide little warning before they break.

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Heres the design and still has to be welded .Fastening the back bracket to the front and the bolts in question ......I also will be using lockwashers and cutting the studs more

 

I'd want to use a thicker spacer, and grade 8 studs, and get the nuts pretty darn tight.

I'm ***uming you don't have any way to add another brace to the alternator? If you can brace it well somehow, then what you have will probably work.

 

Spacer is an 1/8 inch thick ,I cut a jack handle and plate is lowes 1/4 which is 3/16 and thats about it . gonna weld all the stud sleeves together ,That way spans both bolts ,instead of one...........

 

I'd check Fastenal for long studs,

 

American grade 5 no problem. The china junk bolts, even so called grade eight are all of variable quality. I have found that the old grade 5 detroit stuff, even if it's 50 years old, is still better than new china bolts. China stainless is really bad. Aircraft surplus stainless is the way to go if you can get it. If its really critical, like on my race car, I spend the dough for ARP stuff.

There is some aggro over the grade marking of china bolts being suspect - just one news blurb...

 

But a grade 5 will bend, and break, long before a grade 8 is even close to failing.

 

i have found that grade 8 hardware doesn't seam to corrode as fast. am i imagining this?

 

Depends on whether the application is shear or tenision. When vibration is also in the equation, flex has it's advantages. A grade 5 will stretch without breaking. Sometimes that's better. Take a grade 5, put it in the vice and bend it back and forth until it breaks. Try the same thing with a grade 8. You might change your mind.

 

usually use a grade 8 in tension applications and a grade 5 in shear applications.

 

Grade #5 is what most OEM brackets are attached with.

There is a lot of misunderstanding out there concerning #5 vs #8 fasteners. A grade #5 bolt is more ductile than a #8, so it will stretch and bend more before breaking than a #8. But.... it takes a lot more force to fail a #8 than to stretch, bend, or break a #5. The #5 looks like it put up a better fight, but that isn't so. #8 bolts are tough and not brittle. If #8 bolts were unsafe they wouldn't be used for bridges, crane booms, flywheel bolts, etc. Aircraft AN bolts are similar to, but slightly weaker than #8 bolts. Because of tighter dimensional and quality control, those high strength AN bolts are the standard fastener on all sorts of all-out hand built race cars. If #5 was better/safer they wouldn't be paying a premium for the aircraft equivelent of #8 bolts.

In a typical bolted joint with dynamic loading, the bolt acts as a clamping spring. The bolt must be properly sized, tightened enough to generate sufficient clamping, and tightened & stretched enough so it has sufficient "spring action" to keep the joint clamped as loads on the joint vary. The #1 way people get in trouble with #8 bolts is when the objects being clamped aren't strong enough to allow the bolt to be tightened sufficiently. In suspension that may happen with bushing inner sleeves. If a #8 bolt fails that doesn't mean #8 bolts aren't as good as #5 bolts. It means that for one of several possible reasons, a #8 bolt wasn't right for that particular situation.

I realize there are those who don't accept what I have posted. At the very least maybe I'll inspire some pondering, or maybe even some research/study.

 

Thanks for the refresher Al, spot on guys!

 

^^^^ BINGO!

Grade 8 is stronger than Grade 5. Period.

 

You guys remember that the OP was about an alternator bracket, right?

 

I am trying to figure out why he is using studs and not bolts? I have the same bracket and I just used some grade 5 with locking washers. What am I missing?

 

I dont think they do ,But Im getting an education here ,If the grade 5 bend I will know it because it will rub the balancer and thats when Ill switch to grade 8 ,I always use grade 8 ,But I didn't feel like running a die down bolts ,Thats all Lowes had.....And maybe tomorrow Ill finish the bracket ,Its tack welded ,As of right now.....Just need to finish weld and then body work ,Prime and paint ,Im on a mission ,And this is my first full scratch build,Was into muscle cars before this ,
And to answer the question above I wanted as much thread in the block as I can , I didnt want to be short and also when I tried to set bolts up in the mockup motor in the car it was difficult to get started and I kept banging frame ,With studs ,Ill have to pull the rad and grill shell and just slide on . Only 4 bolts ,But no scratched paint ..........

 

This is spot on when considering the alternator application. If we were discussing flywheels then it would be different.
Alternators cause all kinds of flex in the mount, this is why the oem use grade 5 in the same application.

Yes, grade 8 is ultimately stronger but not necessarily better.

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Why skimp on this,go G8!