Lotus Elan

GR 8 suspension?

PostPost by: rdssdi » Sun Apr 05, 2009 5:16 pm

What is the consensus on using Grade 8 verses Grade 5 fasteners for attaching suspension arms to the chassis and hubs. For example I used AN grade thin head bolts for the bottom of the rear bearing carriers. Purchased from Dave Bean. AN is similar to which "grade" fastener?

What would the recommended hardness be for washers that are used in the same application. I assume hardness is important as compressing the washer would loosen the fastener.

Bob
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PostPost by: SADLOTUS » Sun Apr 05, 2009 7:33 pm

er.....with reference to CSI - Grissom says they used Grade 5 when they should have used Grade 8...... the suspension failed and the bus went over the barrier......but.....I smell foulplay.


also:
http://www.rockcrawler.com/techreports/ ... /index.asp
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PostPost by: cabc26b » Mon Apr 06, 2009 2:18 pm

IMHO - I would stick to AN ( typically exceeds GR-8)when possible and maybe fall back to Grade 8 where you can't source AN fo the application. I would not go the grade 5 route. I more confident in the consistency of the AN over grade 8 hardware plus I try to keep to having fasteners with the proper grip and the AN system lends itself to that. Lastly, on washers - there are a whole series of AN washers that compliment the bolts.

George
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PostPost by: gerrym » Mon Apr 06, 2009 10:07 pm

For UK readers, vast majority of UNF or UNC fasteners are available to BS1768 (1963) as grade "S". Occasionally Grade T Higher strength or Grade R are available. Grade S is marginally stronger than American grade 5

Generally, this was the specification that the fasteners were supplied to. I suspect that if keeping to the original design and components, tyres etc, there are only a handful of fasteners that would justify the much greater expense (at least in the UK ) of using AN fasteners. For me, the higher stressed fasteners include those in the transmission. The setscrews that fasten the front disks to the hubs might be another.

However corrosion protection is another matter. These BS1768 fasteners are generally only provided with a thin zinc-plating. This is not sufficient for automotive practise, at least when used on roads treated with salt. I personally apply Denso tape where possible, or a domed nut over the end of an exposed bolt thread, plus liberal use of copperslip. The AN fasteners are by comparison much superior in this respect.

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Gerry
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PostPost by: Elan45 » Tue Apr 07, 2009 3:12 pm

I don't know where some of the information is coming from that is being reported as fact, but AN bolts are more nearly the strength of grade 5. Up 'til the metric conversion of the US auto industry, grade 5 was very common, except for certain special applications such as brake discs and flywheel bolts and of course some internal engine fasteners.

The BIG advantage of AN bolts over any other is that the grip lengths, the length under the head to the threaded end, and the fact that they are nice and smooth and don't have threads cutting into the parts they are fastening. The rear suspension bolts are a great place to see the reasoning. Typically, AN bolts do not have thin heads. Perhaps DBE is modifying them or supplying MS bolts with thin, dimpled heads.

I've seen applications where super bolts such as gr8 and "Supertainium" etc have been mis-applied and failed resulting in destruction of the components they were holding. They don't like to be loaded in shear at all.

BTW, I've bought many AN bolts over the years. Both my Lotus Eleven Ser 2 LeMans and Lotus 20/22 Formula Jr have them on every suspension component and any other critical location. There are a few on my street Elan, but most are normal gr5. The rear suspension is one location you'll find something other than gr5 on my Elan. I am also a firm believer in copper based Never-Seize or Copaslip.

Roger
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'67 Elan FHC pre-airflow
'67 Elan S3 SE upgrade to 26R by Original owner
'58 Eleven S2 (ex-works)
'62 20/22 FJ (ex-Yamura)
'70 Elan +2S RHD
'61 20 FJ project
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PostPost by: rdssdi » Tue Apr 07, 2009 5:30 pm

So...there is no consensus. I agree that AN fasteners are closer to GR 5 than GR 8.

It was my understanding that GR 8 are "fragile" in shear load only at their maximum torque loading.

I will use either GR 8 or AN or GR5.

I will buy Smiths fastener book also.

Bob
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PostPost by: cabc26b » Tue Apr 07, 2009 7:34 pm

Sorry I can see I was not specific enough - The AN/MA/NAS hardware i use is made of 4037 or 8740 alloy ,( The NAS alloys may be different) , they are finished per spec QQ-P-416A, type II class 3 Cadmium plating. Minimum tensile strength runs from 125,000 to 160,000 PSI depending upon exact spec. sort of in the middle then when you compare on minimum tensile - However the AN/MA/NAS spec does have a shear rating where as I recall SAE not providing or requiring one , so at the same time maybe a better spec ? Another thing I would add is that when I buy from suppliers that sell this gear, I know what I am getting, I can't always say that when I buy a "Grade 5 or Grade 8" bolt out of a bin at NAPA.

Lastly Roger brings up a good point on the elan , however , I would also like to point out that since there is really not a lot of hardware involved in fitting out as elan, spending the extra bit to go with known specification hardware correctly sized makes sense to me ( diff mounting, and outer bolts in the front, rear susp, engine mounts what are talking 20-30 sets ??) .

George
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