Lotus Elan

Making Instrument Work Easier

PostPost by: awatkins » Fri Jun 05, 2020 8:04 pm

I've had all four instruments on my S3 in and out several times recently for various reasons and implemented a couple methods for making this easier.

Knurled Fastening Nuts: as you may be aware these disc-shaped nuts and the instrument studs are threaded to an archaic thread standard (British Association). Moss Motors carries them in two sizes but at least for my car they are mislabeled. All of the instruments in my car need 3BA nuts (Moss 360-370), and do not use the 2BA nuts (Moss 360-370) which are larger and labeled by Moss as being used for Tachometers and Speedometers. Perhaps on an MGB or something. And from Moss they are rather expensive ($3)

However, I purchased from British Metrics a 3BA tap and used that to re-tap some larger brass knurled nuts from McMaster Carr (92741A110 ) which I find much easier to manipulate than the thin circular Smiths nuts.

Grounding: Normally when we go to fasten the instruments to the panel we need to find one or more ground wires for each instrument to fit over the end of the instrument stud beneath the circular nut. This has always seemed harder than necessary and not particularly reliable electrically. I sourced some 3BA nuts from https://www.britishmetrics.com and with #6 aluminum spacers McMaster-Carr (92510A461) fastened the ground wire terminals to the bottom of the instrument stud. This leaves grounding and mechanically fastening the instrument to the panel as wholly independent operations so the instrument can now be partially removed and reinstalled without disturbing the ground circuit and also makes the mounting operating itself much easier since no wires are involved.
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PostPost by: el-saturn » Fri Jun 05, 2020 9:33 pm

----------------- with a 99% good feeling: my oil gauge´s stud was messy and at 3,85mm dia. its an M4by swiss standards - i "recut" the stud by thumb and index finger and thereafter the ally knurled NUT fitted perfectly ------------- was i possibly too optimistic or too stupid to have a perfect result, chaps???? or could they simply be M4? sandy, alps my newly fabricated + ported head 41,3/36,5/11mm (20hrs at least) made the engine louder and starting procedure changed - + more grunt ----------- QED/burton + my humble self
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PostPost by: awatkins » Fri Jun 05, 2020 11:02 pm

It is no doubt possible to force a metric fastener onto the stud, but it did not start out as a matric thread.
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PostPost by: awatkins » Sun Jun 07, 2020 7:27 pm

One exception: the speedometer's studs are not long enough to allow for the spacer and nut at the bottom need to establish a separate ground. Possibly bending or otherwise modifying the hold-down arm would allow it, but the LHS stud of the speedometer is so easy to access it hardly seems worth it.
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PostPost by: Andy8421 » Sun Jun 07, 2020 7:41 pm

awatkins wrote:It is no doubt possible to force a metric fastener onto the stud, but it did not start out as a metric thread.

Strangely enough, BA did start out as metric based thread, although not compatible with modern metric fasteners:

https://en.wikipedia.org/wiki/British_A ... ew_threads
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