Lotus Elan

Thread pitch of nuts & bolts

PostPost by: The Veg » Sun Feb 18, 2018 2:40 am

I'm getting ready to start putting the front end back together and I plan to use all new fasteners. This may be a dumb question, but how important is the pitch of the threads of all these nuts & bolts in the front end? The reason I ask is that from local sources I can get the right diameters and lengths but not as fine a pitch as the original items. Assuming that I'm going to be using nylon-insert nuts that should stay well-put, is there some engineering reason for such fine pitch that I'd better stick with it and order these fasteners rather than use what's locally available?
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PostPost by: rgh0 » Sun Feb 18, 2018 2:56 am

The thread size and pitch and grade of the fastener is critical and should not be changed unless you are an experienced fastener engineer and you believe there is a better component

Typically Lotus fasteners are either UNC coarse thread or UNF fine thread which were standard in the British car industry at the time. UNC will normally be used when a bolt is going into a threaded aluminium or cast iron casting. UNF normally will be used when a nut is fitted.

Dont fit other types threads such a BSF or Metric even if they fit in the hole as the fit will be not quite right and the random variations will make future work difficult. Many ( most?) European and Japanese cars use metric dimension and threaded fasteners now so these are probably more readily available but are not correct usage and will cause problems.

The material grade of the fastener is also critical. Most fasteners used on a Lotus should be grade 5 which for the UNF and UNC standards has 3 radial lines on the head. Fasteners without the material grade lines are normally of lower quality and should not be used.

There are many other subtle issues with fastener usage so try to stick with the original thread, material grade, overall length and thread length, especially for anything safety critical such as suspension, steering and brake components.

cheers
Rohan
Last edited by rgh0 on Sun Feb 18, 2018 4:02 am, edited 1 time in total.
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PostPost by: CBUEB1771 » Sun Feb 18, 2018 3:35 am

I agree with everything Rohan said here. A good automotive parts store should have everything you need in terms of bolt nominal diameter, length, pitch and SAE grade. In many cases at the front end you won't have any choice. For example the nuts for the inboard ends of the upper and lower control arms are 1/2-20 UNF, end of story. Assembling the outboard ends to the upper ball joint and lower trunnion and spring/damper unit involves bolts and nuts and so you could use UNC rather than UNF but I would not for the reasons that Rohan provides.

My preference is to take the time and get the right lengths of AN airframe bolts from suppliers like Pegasus, www.pegasusautoracing.com. Using AN bolts you can set up the assemblies so that shear forces only go through the unthreaded bolt shank. In most applications Lotus used bog standard automotive bolts which resulted in shear forces going through threaded sections. Not optimal, but acceptable practice. When ordering AN bolts I usually get two grip lengths shorter and two longer than might seem ideal at first, there is always a little bit of trial and error. AN bolts from suppliers like Pegasus are often no more expensive than conventional SAE Grade 5 bolts found at the local automotive parts store. This way you end up with a decent stock of fasteners so that you won't get caught out when you need a bolt on Sunday evening after the auto parts store is closed.
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PostPost by: mbell » Sun Feb 18, 2018 3:44 am

I am normally able to get them from Lowe's, they have a ok selection of unf bolts in the draws in the hardware section. Home Depot is similar but not as good in my experience. Or you can find a local bolt store.

Only problem I've had is if I am after a specific shank length, then your probably look at an bolts from the internet as suggested.
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PostPost by: The Veg » Sun Feb 18, 2018 4:24 am

Thanks gents; sounds like good advice. I'll definitely stick with the original specifications.
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PostPost by: Craven » Sun Feb 18, 2018 12:03 pm

Shank length or unthreaded section of bolts is critical in many applications, most if not all of the Elan steering components were lifted straight from Standard Triumph cars a mass manufacture.
Quantities of fasteners use was such that bolts were made for specific situations, the like of RUBERY OWEN manufactured millions of special fasteners for the British car industry.
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PostPost by: Bud English » Sun Feb 18, 2018 4:03 pm

In the US, I also like Pegasus along with the Bon Aero division of Dave Bean Engineering or, in a pinch, Fastenal or McMaster Carr for hardware that I can't get locally.

The problem that I have locally is finding UNF fasteners that aren't grade 8. Stronger isn't always better in all applications, so also stick with the correct size, pitch and grade IMHO.
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PostPost by: prezoom » Sun Feb 18, 2018 5:22 pm

I use Coast Fabrication for critical nuts and bolts. I never place the threaded portion of the bolt in shear. With the correct grip length, even if it is a bit on the long side, AN washers come in two thicknesses, .030 and .060. That way you can shim to accommodate the correct thread length. I also use twelve point bolts on the drive shaft flange to differential flange along with jet nuts. These require a chamfered washer under the bolt head. The nice thing about these bolts and nuts is, the wrench size is reduced to where they are easy to use. Coast Fabrication has a nice catalog that has all sorts of different fasteners and other bits. On line at coastfab.com
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PostPost by: Craven » Sun Feb 18, 2018 5:57 pm

Typical difference between stock & original fitment ( lower in pic ) same size bolts.
p1020798.jpg and
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PostPost by: RichardHawkins » Sun Feb 18, 2018 7:01 pm

Very interesting. I struggle with purchasing Unified fasteners here in the UK, and had assumed that purchases in the USA would be easy.

There is a book by one of your countrymen that makes interesting reading. I am away from home at the moment, and am not sure I have this correct, but it is something like:

Nuts Bolts Fasteners and Plumbing. by Carol Smith

Hope that is close enough to identify,

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PostPost by: awatkins » Mon Feb 19, 2018 12:32 am

Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook (Motorbooks Workshop) (Paperback)

No longer in print but available from Amazon for about $30 US.
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PostPost by: rgh0 » Mon Feb 19, 2018 11:06 am

awatkins wrote:Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook (Motorbooks Workshop) (Paperback)

No longer in print but available from Amazon for about $30 US.


Compulsory reading if your into rebuilding or maintaining your own cars. i am a mechanical engineer and I spent a time working for a bolt manufacturer and lots more time working on bolting problems in petrochemical construction and maintenance but i learned a lot I did not know I did not know from this book :lol:

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PostPost by: fattogatto » Mon Feb 19, 2018 2:48 pm

Quickest and extremely reliable source in US is Wicks Aircraft (http://www.wicksaircraft.com/index.html) - usually 1 - 2 day service with standard UPS. (That depends on where you live.) Also, Spruce Aircraft (http://www.aircraftspruce.com).

Not only for hardware but for all metals, tools, and hard to find parts suchas cable hardware, small rod ends, etc. Free catalogues which have a lot of great info in them.
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