CaptainWow
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 posted on 13/11/12 at 10:08 AM |
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Do all bolts need to be 8.8 grade or higher?
Hey people,
Do all the bolts on a kit car have to 8.8 grade or higher or is just for the seatbelt mountings? I had a quick search through the IVA manual and the
only reference to bolt grades is in the seat and seatbelt mounting section.
I have a load of Stainless bolts in marine grades (A2 etc) that I would like to use to help resist corrosion, especially on the front sus, can I not
use these or can they only be used in not structural areas?
Any help apprieciated.
Cheers.
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RichardK
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| posted on 13/11/12 at 10:14 AM |
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I personally wouldn't use stainless on anything to do with safety or high clamping force, everything else go for it!
Cheers
Rich
Gallery updated 11/01/2011
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Bluemoon
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| posted on 13/11/12 at 10:35 AM |
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quote:
Originally posted by CaptainWow
Hey people,
Do all the bolts on a kit car have to 8.8 grade or higher or is just for the seatbelt mountings? I had a quick search through the IVA manual and the
only reference to bolt grades is in the seat and seatbelt mounting section.
I have a load of Stainless bolts in marine grades (A2 etc) that I would like to use to help resist corrosion, especially on the front sus, can I not
use these or can they only be used in not structural areas?
Any help apprieciated.
Cheers.
I would not use them on the suspension; unless you specifically designed it for them... My inspector checked to see that the thing was safe; i.e. I
would expect to see 8.8 bolts on all load bearing parts; possibly higher in some places (caliper bolts ect)..
I stuck to what ford recommended for donner were required...
Dan
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40inches
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| posted on 13/11/12 at 10:53 AM |
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^^^^^^^^Save the stainless for cosmetic only.
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CaptainWow
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| posted on 13/11/12 at 11:03 AM |
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Cheers for the advice, I will get some more 8.8 grade zinc fasteners for the important stuff.
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mcerd1
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| posted on 13/11/12 at 11:06 AM |
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I wouldn't call any A2 stainless bolt 'marine grade' they need to be at least a A4 to have any chance in salty enviroments
(I'm designing bits for offshore platforms at the moment)
its like calling aluminium alloy 'aircraft grade', but folk forget there are lightweight, low strength aircraft grades for non-structural
bits....
also the A2/A4 part of the grade is only the corrosion resistance, the number in the grade (i.e. A2-70 or A4-80 ) tells you which class
of bolt it is and therfore the strength
even though an A4-80 is approx. the same design strength as an 8.8, in reality they have quite different failure behavior so you can't just swap
them - it all comes down to the true elastic limit vs the 0.2% proof stress
most car makers (inc ford) use 10.9 bolts on most structural parts, but its a ballancing act if you go too strong you'll losse the
toughness/ductility
(i.e. would you rather a saftey critical bolt bent/streched a bit when it failed giving a little warning or would you rather it just let go completly
with no warning  )
with 4.6, 8.8, 10.9, 12.9 grades the higher the first number the stronger it is, but the higher second number the less it will strech before
failing
[edit]
if money is no object you could get some 'BUMAX 88' bolts, never used them myself but they claim to be direct replacments for 8.8's
[Edited on 13/11/2012 by mcerd1]
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britishtrident
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| posted on 13/11/12 at 11:31 AM |
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As above my understanding is especially avoid using stainless bolts in situations where they are loaded in shear
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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smart51
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| posted on 13/11/12 at 12:29 PM |
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Would it be acceptable to use a bigger size bolt in stainless, for example an M12 in A4-80 rather than an M10 BZP in 8.8?
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mcerd1
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| posted on 13/11/12 at 02:24 PM |
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quote:
Originally posted by smart51
Would it be acceptable to use a bigger size bolt in stainless
I suppose you could, but as to how much bigger it would depend on the loading etc...
basically redesign the whole thing for stainless bolts
I think you'd be better off buying the expencive '8.8 equivelents' or just getting 8.8's with a better anti-corrosion coating
(passivated zinc plate ? )
[Edited on 13/11/2012 by mcerd1]
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britishtrident
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| posted on 13/11/12 at 05:04 PM |
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Where the bolts are well over sized no problem but bigger diameter bolts have to tightened to correct ( ie greater ) torque or they will tend
to work loose more easily, strange but true all to do with the amount of elastic stretch the bolt experiences when it is tightened. So using thread
lock or locking tabs is advisable.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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