blakep82
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| posted on 28/9/08 at 06:02 PM |
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when should or shouldn't you use certain bolts
what i mean is, i never used to really see the point of allen key bolts, but they really do look better than normal hex bolts, so i've started
using them wherever i can, but should i be using them for things like engine mounts?
silly question perhaps, but is there any right or wrong time to use them?
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Howlor
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| posted on 28/9/08 at 06:13 PM |
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Most allen bolts are 10.9 standard IIRC, therefore often better than most standard hex as they tend to be 8.8's unless otherwise specified.
Steve
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matt_claydon
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| posted on 28/9/08 at 06:31 PM |
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Sometimes a particular head type makes access for tools easier (e.g. when the head is in a counterbore you need allen or Torx, if there's a
restriction above the head preventing access with a socket or allen key then hex may be better as you can still get a spanner on), but otherwise as
long as they're the correct grade (or better) then it doesn't really matter.
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blakep82
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| posted on 28/9/08 at 06:35 PM |
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cool. allen bolts it is then. there's some nice 12.9 grade zinc plated steel bolts on ebay. i'll get some of them. i guess i should use
spring washers on them too?
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Alan B
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| posted on 2/10/08 at 12:09 PM |
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When I used work back in the UK designing newspaper printing equipment we would get bollocked for arbritarlily calling out hex socket (Allen)
fasteners when regular hex heads would work fine...it seems there was quite a cost difference when multiplied by several hundred.
Not that this helps you at all...I'm just lonely today and felt like joining in....
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AlphaX
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| posted on 2/10/08 at 12:21 PM |
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12.9 zinc plated bolts can't exists. I've been told that it is technically almost impossible to guarantee the 12.9 strength when it is
zinc plated. I've seen 12.9 bolts that were Boromite plate (?) and they had a bit of vage grey color, and weren't smooth finished. These
were also very expensive!
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iank
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| posted on 2/10/08 at 12:35 PM |
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quote:
Originally posted by AlphaX
12.9 zinc plated bolts can't exists. I've been told that it is technically almost impossible to guarantee the 12.9 strength when it is
zinc plated. I've seen 12.9 bolts that were Boromite plate (?) and they had a bit of vage grey color, and weren't smooth finished. These
were also very expensive!
Namrick say their 12.9's are zinc plated
http://www.namrick.co.uk/browse.asp?PCID=10
(as do screwfix for that matter, but I wouldn't try to use them as an example).
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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clairetoo
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| posted on 2/10/08 at 08:07 PM |
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The problem with zinc plating hi-tensile bolt's is hydrogen embrittlement - bubbles form under the plating , causing stress points that
seriously weaken the bolts and do cause sudden failure ( I found this out because I used to have all my bike bolts chromed , and I had a lot of engine
mount bolts fail...)
The cure is low temp heat treatment over a long time - low enough not to damage the bolts or plating )
That's how I understand it , anyway 
Its cuz I is blond , innit
Claire xx
Will weld for food......
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blakep82
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| posted on 2/10/08 at 08:22 PM |
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i got the steel ones that are black in colour. don't know why they're black. but they are stamped 12.9 so should be plenty strong enough
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blakep82
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| posted on 2/10/08 at 09:20 PM |
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can i use them for bolting manifolds too
i suddenly love them for some reason
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:{THC}:YosamiteSam
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| posted on 3/10/08 at 07:14 AM |
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what you have got to watch is the fasteners your replacing - the original spec will have a torque value - dont forget to torque it up with a allen
socket
might be something you already know but bolts when torqued correctly are under elastic tension - IE they are stretched - this stretch will
'clamp' the part its holding so it aint coming loose - you will find bolts such as 12.9's will be used for really high and vital
fasteners - such as flywheel bolts, prop bolts, driveshaft flange bolts.. that sort of thing.. suspension bolts can be 8.8 with no problem - its a
matter of using the right torque for the right application.. very important to not have stuff like wishbone bolts falling oot..
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02GF74
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| posted on 3/10/08 at 08:24 AM |
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interesting question.
flakmonkey should know the answer?
one instance that I can think of where you would want to use a cap head is if you are fixing a box section - the hole in the outer section needs to be
just big enough for the cap head to pass through whereas for a hex head, it needs to be much bigger so that the socket can get past.
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Fred W B
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| posted on 3/10/08 at 08:46 AM |
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Just be aware the black ones will rust in a moment.
I use black, but have them zinc plated once any shortening is done.
I know that that is not correct for ultimate strenght but most bolts in a chassis are so overkill for the application is doesn't seem to be a
problem
Cheers
Fred W B
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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smart51
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| posted on 3/10/08 at 10:13 AM |
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quote:
Originally posted by blakep82
i got the steel ones that are black in colour. don't know why they're black. but they are stamped 12.9 so should be plenty strong enough
Black is described as "natural colour" I think it is because the steel is coated in oil and the heat of the steel causes the oil to
blacken. It is enough of a coating to stop the bolts rusing in the box between the factory and shop but unless used in a dry indoor environment, the
bolts will rust before long. They need to be degreased and painted.
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02GF74
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| posted on 3/10/08 at 10:45 AM |
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^^^^ self-coloured.
painting them stops rust.
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blakep82
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| posted on 3/10/08 at 11:27 AM |
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got some nice gloss black paint waiting
was going to paint the block today. engine mounts need painting anyway
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flak monkey
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| posted on 3/10/08 at 12:10 PM |
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12.9 cap heads are overkill for most applications in our vehicles, with the exception of perhaps flywheel bolts, they do look nice though. (Even then
these are normally 10.9).
There is however no problem using them.
With regards to torquing fasteners correctly. The quoted max torques for fasteners arent always suitable to use. If they are into cast iron or mild
steel you will rip the threads out of the part. However if they are into the appropriate nuts then you can torque them up to the max if the
application calls for that much clamping force.
The max torque is based on stretching the bolt to approx 70% of its yeild strength. At this point you are getting massive clamping force (ideal for
suspension pivots etc) which is very easy to calculate. At torques lower than this you are getting steadily less clamping force. Not all applications
need the highest force a bolt can give (such as gasketed joints etc).
In essence use whatever bolts you like, as long as they are at least the same tensile strength as the ones they are replacing, and torque them to the
manufacturers recommended specification for that application.
Stainless bolts are not suitable in highly loaded applications, not due to their tensile strength, but because stainless steel suffers heavuily from
fatigue at loads well below its yeild point. Steel bolts do not suffer the same problems.
As for colouring. Self colour (the black ones) rust quickly as all the black is is burnt on oil from the heat treatment process. Zinc (BZP) are best
as they wont rust but as others have mentioned there is the embrittlement issue. However most bolts on our cars are so over specced this is never
going to be an issue.
Lastly, dont be tempted to put antisieze on bolts before torquing them up, unless it is specifically requested, as this increases the preload you are
giving which could cause issues in some cases.
David
Sera
http://www.motosera.com
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