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Torsion bar framehead bolt strength
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ghiachimp
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Location: Kent, UK
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PostPosted: Mon May 13, 2024 3:33 am    Post subject: Torsion bar framehead bolt strength Reply with quote

So yesterday I fitted some caster shims and replaced the bottom two framehead bolts with longer ones.

I noticed the old bolts were 8.8 grade but my replacements are 10.9.

I understand the 10.9s are stronger but after doing some research last night (youtube etc.) someone had suggested 10.9s could be more "brittle" and prone to fracturing due to the hardened metal being less malleable that the 8.8s.

So question is: do I need to worry? Should I replace the new 10.9 bolts with 8.8 grade ones?

Thanks!
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baldessariclan
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PostPosted: Mon May 13, 2024 5:30 am    Post subject: Re: Torsion bar framehead bolt strength Reply with quote

I personally wouldn't worry about it. While there is indeed a slight loss of "toughness" with those higher strength bolts, for that particular application doubt it will see high enough loading where brittle fracture is a realistic failure concern. Just make sure to torque them to the correct specifications, and protect from (or at least keep an eye on) rust/corrosion development.
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ghiachimp
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PostPosted: Mon May 13, 2024 9:56 am    Post subject: Re: Torsion bar framehead bolt strength Reply with quote

Thanks for putting my mind at rest.

That said I didn't use my torque wrench to tighten them... just put a lot of welly into it Very Happy

...and if 36 lb/ft is correct (doesn't seem much), I've probably over tightened them.

Will need to check & most likely loosen them a little I think!
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Busstom
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PostPosted: Mon May 13, 2024 10:48 pm    Post subject: Re: Torsion bar framehead bolt strength Reply with quote

ghiachimp wrote:
...someone had suggested 10.9s could be more "brittle" and prone to fracturing...

MASSIVE fallacy.
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cory464 wrote:
if you aren't perfectly centered in the hole you will have issues when you tap it.
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DesertSasquatchXploration
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PostPosted: Tue May 14, 2024 9:51 am    Post subject: Re: Torsion bar framehead bolt strength Reply with quote

We use 10.9 a lot on custom automated machines they can take a shock load and hold tight, 8.8 stretch and come lose, 12.9 snap like match sticks.

I have 10.9 bolts on my front beam its still attached.
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ghiachimp
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PostPosted: Thu May 16, 2024 3:59 pm    Post subject: Re: Torsion bar framehead bolt strength Reply with quote

Thanks for your replies and setting my mind at ease. I’ll stick with the 10.9s Laughing
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