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MG Midget and Sprite Technical - Tensile strength

I am sure this has been discussed before, but is there anywhere a listing or table of what strength bolts and set screws to use on different locations on these cars?

The standard for graded supplies from reputable suppliers seems to be Grade 5 (8.8) which I assume is suitable for pretty well all applications. But there are some such as the front spring pan set screws and the prop shaft UJ flange bolts which I believe would need to be Grade 8. But where is this listed? - or where is there a chart of where such higher grade fasteners should be used?

For longevity, I am considering using SS, at least in the more visible spots as even zinc plated ones deteriorate quite rapidly. SS would only be suitable where a Grade 5 is sufficient, but not as an alternative to Grade 8 bolts.

As I understand it a class 80 (A2 or A4 grade) SS bolt has the equivalent strength to a normal Grade 5, and class 70 is about 15% weaker which for bodywork assemblies is probably close enough.


( I am of course ignoring the general DIY stores packs of "putty bolts"! )
GuyW

Guy, for a road car I think Grade 5 will be fine even for the two specific uses you mention. On the race car the only places I use special or high grade bolts is engine internals and the roll cage, otherwise I just use what's to hand. Should add that I rarely buy new but clean and re-use original parts. including fasteners.
David Smith

The steering rod clamp bolt is 11.1 as are the bolts for the Armstrong front shocks to the body. I have seen sprites where they broke with 8.8 (lucky enough not mine).
Off cause some motor bolts (flywheel, big ends etc.), and some disk brake bolts are 11.1 as well. I did not know that the spring pan bolts had to be high tensile steel.
Flip Brühl

Thanks. I wasn't really meaning specific engine/ gearbox/ diff bolts, more the general assembly type as used in bodywork, fuel tank etc.

I had only picked up the spring pan bolts from dire comments made here in the BBS by others. It may not therefore be true!!

Good to know that quality Grade 5 will do in most, if not all, applications. Are nuts similarly graded? Suppliers like Grove Components whom l have often bought from just list them all as Grade 1, whatever that means.
GuyW

Flip,

You may want to check your information about 11.1 as that would be a fastener of 1100N/mm^2 ultimate tensile strength (UTS) and a yield strength of 110N/mm^2 as the number after the '.' is the % of UTS in 10s so an 11.1 fastener would be about as useful as a chocolate teapot.
David Billington

Speaking on this side of the pond, The the price differsnce and avialbilty is worth using grade 8 on anything where structural forces are at play for simple attactment hardware like like the timing chaing cover i use stainless steel and on some areas like the bolts for the thermostate housing ive gone to chrome with great success, and some expense but ill never have those 3 bolts rusted, and sheared off agian in the head agian .... and it has the add bling bling eye candy appeal

Grade 5 is only a couple pennies cheaper then grade 8 and is also much more rare for any thing beyoud the most basic sizes and shapes... and in some cases even more expensive the grade 8

I needed button screws to hold the ring gear on to my aluminum fredenza flywheel... and grade 5 was off the hook uber expensive and special order over grade 8, in stock ... not that i wanted grade 5 forthat application

But ...here i guess its universial marketing we just have better access to grade 8 due to our agricultural background in community.

For the suppiers its less instock inventory to maintain, and a few pennies more profit and less issues of failure for the customer meaning better over all customer service in quality

Grade 8 is is more expensive the pot metal hardware but it last forever and the stsknless is even more expensive but never having to replace or have it seize up or rust is a godsend esp on areas that is simple attachments with a smear of anti siezure compound ...

lets face it, these cars are always needing taken apart and put back togather... make it easy the 1st time

The added expense id of replacing regular hard ware over time with grade 8 or stainless for every nut and bplt has got to be less then $200 over the stsndard stuff doing that over a period of 10 years you hardly feel the prick

Just my 2 scence

Prop
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To answer your question guy more directly...yes there is a chart ...i may have one in my phone butit will tqke a few days to find it

You might try (fastnel) here in the usa, there a huge supplier of all things hardware im certian they have a charts of all the vwrious tensil strengrhs for various grades of hardware types, sizes and shapes

Prop
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Haynes manual has a section dedicated to all the hardware used in the midget

I want to say 13 diffent bolts are used in the midget to hold it all togather

Hopfully that helps a bit to orgwnise the thought process

Prop
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The old SAE J429 Grade 5 equates to the new metric ISO 898-1 (8.8) Medium Carbon Steel
J429
The old SAE J429 Grade 8 equates to the new metric ISO 898-1 (10.9) Medium Alloy Carbon Steel.

That equates to proof stress ie when the material just starts to deform and any company will put a factor of safety in there in order never under normal circumstance will the fixing be deformed, in this case they will increase the fixing diameter.

Guy you appear to be looking at the tensile strength of the fixing which is where the fixing fails.

YOU DO NOT DESIGN TO THE TENSILE STRENGTH OF THE FIXING.

No where you are getting it wrong is to look at the tensile strength of the SS fixings.

You have to design to the proof stress and these for stainless steel are below the carbon and alloy steels properties mentioned above.

Also the SS is more brittle than the carbon and alloy steels and should be avoid on cars unless you do a design check on each case. Further when you are in a hurry we all just use the bolt that fits the hole or is the size of the one that was taken out. No one looks at the material markings.

Do not use stainless on a car to be safe.

Eddie Cairns

Guy, what were you thinking ?

You were just going to wing it werent you?

Buddy everything eddie said, you got yourself 6 midnights of advanced mathmatics calculatiins to do long before you ever should be considering the purchase of hardware.

Break out rhat old college physics text book and remember to wear safety glasses when using the slide ruler and pensils as the russian hacker says "use safety glasses, safety is priority number 1

Seriously guy ? Tis tis tis

Prop
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No Eddie, l am not designing anything. My questions were so as to find out from others with practical experience what specification bolts to order. I wouldn't anticipate tightening any of these bodywork fixings to the point that the bolts shear. Unless l was just being ham fisted!
GuyW

Guy,

I am reasonably confident that the nuts are indeed graded. Also, if you look for the chart at the company that Prop was suggesting, note that some of us are aware that Prop's spelling is at times suspect. In this case, the company that he refers to is Fastenal.

Charley
C R Huff

No you are not designing but it is not clever to put your head in the sand and use stainless steel bolts in a car.

If people advise from whatever source that a specific bolt is not heavily stress then use type 5 or 8.8 the easy material to get is in certain cases 8.8 fixings which are now appearing in UNF sizes.

Again I will say even you do not like it, do not mix carbon steel and stainless steel as you will end up buying SS in bolt sizes that can be used in stress situations.

Many vendors are using these SS fasteners as standard and they are not up to the strength requirements needed in heavily stressed car situations and you like everyone else will use the wrong material and it may be serious.

If that annoys you Guy, that's fine with me, you have been warned!

Don't reply to this message as you know the correct thing to do.
Eddie Cairns

Eddie,
I will reply. I am not "sticking my head in the sand" as you put it. If I was, I wouldn't have posed the question asking for information in the first place! What I was asking for, if you care to check, was information on what stress grade bolts were required to be used, and where.

Although you clearly understand the physics and metallurgy concerned, you haven't provided any tangible answers to this other than to say don't use SS bolts. But without the original design requirements I don't understand how you can be so adamant in every case. Maybe you are correct, but you clearly don't have the evidence to support your contention.

I do however, thank you for your input. It adds to the debate.
GuyW

Useful info in:
https://www.amazon.co.uk/Fasteners-Plumbing-Handbook-Motorbooks-Workshop/dp/0879384069

Mike

M Wood

Come on GUY,

EDDIE has a valid point, never ever use stainless steel in a car for any reason

Guy, If you use SS to hold the clamping braket of your water temp/ oil pressure gauge and that nut breaks off while crusin thur chucky cheese pizza parking lot, just think of how bad you will feel that stianless steel nut breaks apart and shoots put from under the dash out the cars interior and into the eyeball of an 11 year old child....god that would be horriable, are you sure you want to live with that, all because you have a prefersnce zfor stainless steel hardware ? Good lord GUY, think about the absurd absurdity of whats being said here


Lets all agree here and now.... no stainless hardware anywhere on or in or near the car, that stuff is as dangerous as magnesium Wheels at a water filtration and Bottling Company

Thank you eddie for being the voice of reason im glad you came along with your valued insightfulness!

By the way eddie, whats your opinion of using a plastic 2 gallon gas can sitting unsecured loosely behind the passangers and the vent fully open as the cars main fuel tank ... good, bad, Indifferant ???

The gas can is red all be it a bit faded with age and direct sun light exposure

Just curious, thanks.

Prop
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Here is a video of my cqrs interior with stainless steel hardware EVERYWHERE... i didnt make note of it in the video but if you watch closely...its there and even a shot of me

Please watch and offer up any ideas you may have to provide safety and counter act agianst all the stainless steel in my car shearing off and contributing to a potentially dangerous life altering situation

Dont mess around people, eddie is correct stainless steel is some dangerous stuff in auto mobiles ....its nothing to joke about and make lite of

Gez ...if look closely at my 52 sec video, you can clearly see a huge chunk of SS is enbedded on my steering wheel ... god what was i thinking... its so dangerous...i cant belive im still alive


Thank you eddie, thank you, you probably saved my life from tje effects of using SS in may car... your the man dude !

http://youtu.be/8CWtHKy9RhQ

Prop

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This thread was discussed between 29/08/2017 and 30/08/2017

MG Midget and Sprite Technical index

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