Torsion cover bolt strength?

[TedzBug]

I didn't find a real specific answer on this one so i'm asking.

How strong do torsion cover bolts need to be with stock covers? I've cleaned and painted my covers and de-rusted the stock bolts, but thought maybe putting stainless socket head cap screws would look nice and avoid corrosion...

Are ones available at my local ACE Hardware up to the task? Or am i in need of higher grade bolts for this application? (not sure what grade the ones at ace are, but can always go to a fastenal or somewhere else local to me to get higher grade bolts if the ones at ace are low)

Thanks

Ted

[crazy tarzan]

I would use grade 8 bolts at least. Whether or not ace has ones that work, I don't know. And I'm not an expert either. NAPA usually has a great selection of bolts--in different sizes and threads, us and metric to boot.

[Ol'fogasaurus]

I talked to a couple of other guys about the fix; my first reaction was Helicoils but then after I did the measuring I thought the bolts would be the best for many reasons; the guys I talked to had mixed reactions too. Nothing less than a grade 5, other than electric stuff, belongs on a car. I don't think you need to go as far as grade 8. Its been a long time but I think the metric 8.8 is somewhere closer to a grade 5 (SAE) than a grade 8 (SAE).

As far as box stores go, I am often very dubious as to their quality but if the fastener is marked with Grade 5 or 8.8 symbols then I guess you have to believe them. http://www.specbolt.com/technical.html

Most box stores, and some specialty fastener stores only stock in 1/4" length and some have specialty sections for metric fasteners; I am not sure what stocking lengths they use but I am sure it is somewhat close to the 1/4" lengths as stocking to the 1/16 or 1/32"lengths that fasteners come in is cost prohibitive.

You want the length of the shank (the unthreaded part) to carry the load, not the threads as they are the weakest part (I am going to give you more information than you want or need just-in-case someone else reading this does need it) with the radius under the head being the second weakest part. Since the bolt will stretch some when tightened you want the thread, when the bolt is in a relaxed state, to be just short of the nut side surface. If that is not possible you can use a washer under the head or up to three washers under the nut side to make up over length differences. This is the proper way to do it. You also want the threads to stick out of the nut no less than 3 full threads also some racing organizations often call for 2 1/2 D in some locations as the minimum pitch showing.

Once tightened down you should be OK.

My opinion Lee

[TedzBug]

Lee. .. im speaking of torsion cover bolts. metric. whats with the inch fraction length references and heli-coil info?

I understand bolts and shear vs clamping loads. (machine and automation designer by trade)

just trying to understand what actual stresses the Torsion cover bolts are taking...

I will make sure grade 5 or equivalent are used. as far as unthreaded portion in a 20mm long bolt? provably wont find that. I believe most if not all 20mm long will be full thread shank.

[TedzBug]

off to Ace to see what grade they carry in stainless...

[TedzBug]

I found my answer.... Stainless A2 is a little better than Inch grade 2. A4 has a little less strength than Inch grade 5.
Maybe i'll just use the originals and paint em.

[TedzBug]

I ended up getting stainless split lock washers, stainless flat washers and grade 10.9 button head cap screws in black oxide. going to torque em and throw a quick clearcoat on them with some anti-sieze on the threads.

[Ol'fogasaurus]

Retired Tech Designer Aerospace. Bolts are available with a shank on them as fully threaded but what I was talking about was another problem; sorry about the confusion. You still do not want the threads in shear or tension if you can help it as the threaded portion is, as I said, the weakest part of the bolt followed by the radius under the head of the bolt.

Lee

[jhoefer]

Anywhere you want bling but need structural strength, you should be looking for chromed steel bolts instead of stainless. For example: http://www.allensfasteners.com/search_r ... aramCat=82

Stainless is fine for low stress apps, but stay with the proper grade (chromed) steel bolts for things like suspension.