Stronger than grade 8 bolts?

[DRJDVM's '69]

Are there easy to find fastners that are stronger than grade 8 ??

The reason I'm asking is that I just broke one off in my aluminum head and dont want that to happen again. Its one of the bolts that holds my pulley system to the head. I broke an original fastner (hex head that came with the kit, assume grade 5) in the iron head about 3 years ago. Replaced that with a grade 8 and no problems.

Today I was putting my pulleys back on the new motor, and used the same grade 8 bolt again with antiseize on it. As I was tightening it with a box wrench, using my finger tips, it just broke off before I even had it cinched down. I was no where near tweaking on it. The only thing I can think of is that for the last 3 years, that bolt has been getting fatigued and just gave way with only mild twist pressure.

So... I'd like to not to have to worry about it breaking off again in the head.

Are the ARP fastners stronger than grade 8 ??

I'd like something stronger that isnt hard to find... any suggestions ??

[vp23271]

Don't know, but someone on this forum will post soon enough.

If not you can always give ARP a call.

I was at a local car show and got a bussiness card for a guy that just sells fasteners. His name was Derek and the name of the company is DMP Fasteners. I have not done business with him, but his website looks pretty complete.

http://dmpfasteners.com/

[Project69]

Im pretty sure the ARP studs are stronger then grade 8 bolts.

[CarlC]

G8 is more than sufficient. Higher ultimate and yield materials are used in specific applications (rod bolts) that are high-stress. An accessory bracket is not. G5 is very common due to lower possiblities of stress corrosion cracking and price.

If the fastener failed during installation with minimal torque applied then something was wrong with it.

Also, a torque wrench is always better than an uncalibrated arm, especially when trying to determine yield points.

[DRJDVM's '69]

It definitely failed with minimal tension....like I said, I assume it just got fatigued over the last 3 years and today was the end of the line.

[DLinson]

Grade 5 bolts = 120,000 psi yield strength
Grade 8 bolts = 150,000 psi yield strength
12 point flange head bolts = 170,000 psi yield strength
Socket head cap screws = 180,000 psi yield strength.

ARP bolts vary in strength
Head bolts and studs are 200,000 psi yield strength
exhaust header bolts are 170,000 psi yield strength
Flywheel bolts are 180,000 psi yield strength

Check out ARP's web site and search for the size you need. http://www.arp-bolts.com/Catalog/Catalog.html

You could look at McMaster Carr and order bolts from there, you'll just have to buy a larger quantity.

You should look into why the bolt is braking and fix that problem instead of just increasing the bolt strength. Maybe something is moving around too much, vibrating, needs more support, etc.

Dennis

[CarlC]

Dennis, your numbers are minimum tensile (ultimate) strength, not yield.

There are a few fastener materials that have a yield in the 180KSI range, and they fly to outer space. They also need government funding to purchase.

Getting the torque right is not an easy thing. There are dozens of variables that can screw things up. Rule of thumb, on a standard coarse-thread fastener with a light lubricant close to 90% of the applied torque is used to overcome friction. Grease or oil help, but ARP recommends their specific lubricant in order to try to minimize variables and achive the maximum allowable tension (NOT torque!)

[Takid455]

I agree with dlusion that you seem to have a problem that needs to be evaluated. increasing bolt strength is just putting a band-aid on the problem. no reason a gr5 can't handle a pulley.

[Fesler built]

We have had this happen before, sometimes bolts just break, nothing you can do about it. Go over all your pulleys and make sure you dont have one messing the system up if not just replace the bolt. Hopefully you wont be the lucky one to have it happen again as I have. G5 is plenty for what you are doing but if you want upgrade to G8 and you wont have problems.

Do you have pics of the bolt you might be able to see if it had problems from the get go.

Good luck

[DRJDVM's '69]

I agree that there appears to be a "defect" in the design, but I dont see a way to modify it. I'm using a Concept One pulley system.

Basically the bracket is like a "Y" with a brace betweent the "forks". The "tip" bolts to the waterpump (bolt goes through pulley and then waterpump and block). On the inside of the "Y" there is a bolt that bolts to the head. Thats the one that has broken twice.

The only reason I can see it breaking is that the bolt was defective (it was a grade 5 the first time and grade 8 this time), or there is just alot of stress being paced on that pulley. If thats the case, I must be putting too much tension on the belt or the design is just flawed.

For piece of mind I'm gonna get some ARP bolts. The extra $$ is worth not having to mess with getting a broken bolt out again.

[protour73]

http://www.totallystainless.com/ their stainless hardware is tested stronger than Grade 8.

[silver69camaro]

Some photos would be helpful here. Something is definetely wrong if grade 8 bolts are failing. A stronger bolt will probably break again, but it would take more time.

BUT, there isn't anything that says a ARP bolt has a higher fatigue limit than a quality grade 8. Just because a bolt is "stronger" (read: higher UTS) doesn't mean it will last longer in this case. Ductility and fatigue strength are major players here.

[protour73]

bolt too long ...... bottoming out and breaking off as a result?

[DRJDVM's '69]

This is the one I have..
http://www.conceptonepulleys.com/long.htm

So everyone seems to think grade 5 should be fine,,, then I use a Orchard supply Grade 8 bolt...... so an ARP seems like the next logical "upgrade" in bolt strength....

I cant change the design.....

[Damn True]

Just remember that anything in shear should be an AN bolt.

[Fesler built]

Looks like a nice kit, is anyone else out there having this same problem? I use Vintage Air front runner and Billet Specialties Tru trac systems and have had no problems thus far.

I think its just a you got lucky problem and found the one bad bolt, no one up here is really stating that they have seen this.

Good luck



This is the one I have..
http://www.conceptonepulleys.com/long.htm

So everyone seems to think grade 5 should be fine,,, then I use a Orchard supply Grade 8 bolt...... so an ARP seems like the next logical "upgrade" in bolt strength....

I cant change the design.....

[go-fish]

I used to work with cranes for the Navy and was made aware of the vast counterfit problem with fastners. Alot of grade 8 fastners out there are not up to the true spec. I will only buy from reputable companies now. For you to replace any fastner on a crane the Navy Crane Center has to have done analasys on the same part number from the company. It is a rediculous process.
Again the least you could do is just order from someone that has the best rep. ARP and McMaster Carr are my favs. Sometimes fastners follow me home from work.

[pitts64]

Try to find some old, never used, American made #8 fasteners.

[67 455 Bird ragtop]

http://www.totallystainless.com/ their stainless hardware is tested stronger than Grade 8.

Not completely true. They have a nice selection of hardware that is stronger than grade 8. I use some of it on my suspension. But the majority of their stuff is normal stainless which is usually only slightly better than a grade two.

[justanova]

I used to work with cranes for the Navy and was made aware of the vast counterfit problem with fastners. Alot of grade 8 fastners out there are not up to the true spec. I will only buy from reputable companies now. For you to replace any fastner on a crane the Navy Crane Center has to have done analasys on the same part number from the company. It is a rediculous process.
Again the least you could do is just order from someone that has the best rep. ARP and McMaster Carr are my favs. Sometimes fastners follow me home from work.


The bolt supplier my dad uses (lawson products) had a tester that they would bring around to sell you on their bolts, you would put a bolt in it, torque it and mesure the stretch,(i belive the sales guy referred to this as yield strength, not sure i was about 9 yrs old) but they would test your bolts and their bolts and their bolts were a lot stronger. their grade 5 bolts were stronger than the grade 8's we were using. needless to say we use nothing but lawson products bolts etc.... now

[Jim Nilsen]

Is the bolt you used a full thread bolt or does the thread stop with a shank up to the head ? If it is going in and bottoming out on the thread at the head at the same time it clamps down hard enough to hold it will have a stress point and you wouldn't know it.

I remember getting a few bolts mixed up and put the long one in the short hole :pat: ,water pump bolts are notorious along with anything else on the front of an engine. Just leaving off a lock washer or flat washer and not using the set together can make a difference in the length on a blind hole.

It is something I would check and it never hurts to chamfer the hole on the head and chase the threads to make it better than new.

Goodluck on finding the cause :cheers:

[CarlC]

For many applications a hardware store G8 will work just fine. Accessories, trim, etc. have little load on them vs. the clamping force available.

I do agree with True that a good bolt should be used for shear and critical applications. Most AN bolts are G5, but when put into full double shear with the threads removed from the shear plane it is stronger than a factory bolt in which the threads are in shear.

Pic up a copy of Carroll Smith's "Nuts, Bolts, Fasteners, and Plumbing" for a good, easy to understand read on such items. Further study of the A354, A490, and BD grade structural bolt specifications is also enlightening.

I would be worried about a G5 testing stronger than a G8. G5 is intended to have a working range of yield stress, ultimate stress, and ductility. To go beyond these for the given metallurgy could spell trouble.

[69stang]

I was trying to understand what you were explaining and looking at the diagram for the pully system on the page you linked to. Two things came to mind. First, it is hard to tell the size of the bracketry. It looked like it lacks some size and robustness which might be letting your accessories vibrate. Like I said, hard to tell from the small pictures and digram. Second, how's the pulley alignment? Are all the pulleys in the same plane perpendicular to the crank CL? Maybe you can post some pics of your engine.

[68sixspeed]

$1 bey says it was an import bolt or some movement causing it to fatigue. We use mostly socket head cap screws for building machinery and will not use import, the heads strip out easy, they can be brittle, all sorts of problems. HoloChrome or Camcar seem to be the best for SHCS; I've gone with ARP on a lot of critical bolts (bell housing, motor mounts, etc.) - US made and from the TV clips I've seen they do a lot of QC testing of the production product.

[DRJDVM's '69]

The grade 8 I used had a short unthreaded shank. The hole in the head is only 1/2 inch deep, and the bracket is 1 inch thick at the mount. The bolt I used was 1 1/2 inch long and I used a washer.

The bracket is actually pretty thick and sturdy. I'll try and post some pix of my motor with a better angle to see the mount etc.