Lotus Elan

Carburettor mounting nut identification

PostPost by: oldelanman » Mon Jul 06, 2020 8:45 am

Can anyone tell me what the markings on these nuts indicate .... thread type or grade perhaps ?
They are 5/16" UNF plain nuts.
IMG_20200706_084326.jpg and
Last edited by oldelanman on Thu Jul 16, 2020 5:43 am, edited 1 time in total.
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PostPost by: Andy8421 » Mon Jul 06, 2020 10:13 am

Usually indicates a left hand thread.

Most commonly used for fuel gas fittings, or in situations where a right hand thread would tend to undo.

Have you tried them on a bolt?
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PostPost by: pharriso » Mon Jul 06, 2020 10:22 am

Andy8421 wrote:Usually indicates a left hand thread.

+1
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PostPost by: oldelanman » Mon Jul 06, 2020 2:15 pm

Andy8421 wrote:Usually indicates a left hand thread.

Most commonly used for fuel gas fittings, or in situations where a right hand thread would tend to undo.

Have you tried them on a bolt?


They are definitely 5/16" UNF right hand thread.
I have searched and found similar markings which indicate the grade of a nut but they appear on all 6 points of the hexagon, not on just the 2 opposite as these are. I wondered if perhaps it's crimping to form a stiff nut or lock nut but I thought that was usually done on the flats, not the points as here.
Anyone seen these before ?
Thanks.
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PostPost by: Fredtech » Sat Jul 11, 2020 8:43 am

Hey Roger. Think they may be "Identification-Marks". Similar marks on older British Built Aircraft, BA/BSF Nuts & Bolts. (Americans use a completely different Identification and numbering system. AN NAS MS etc)

CAIP's (Civil Aircraft Inspection Procedures, give you a fuller picture)

https://archive.org/details/CAIPPART1/p ... 3/mode/2up
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PostPost by: oldelanman » Sat Jul 11, 2020 3:50 pm

Hi John (Freddie),
Thank you for posting that link.
The nuts I have are definitely UNF and the identifier marking shown for that in those standards is different so I think my markings mean something else.
They are used on my S4 for the Stromberg carb and adaptor plate mounting and are original fitment as far as I know.
I've done a bit more research and came across this description...

Two-way Reversible Lock Nuts
A two-way reversible lock nut is a hex nut with two or three, round or rectangular indentations, compressed onto the flat sides of the nut equal distances from each other. The compressions create slightly distorted center threads resulting in a controlled locking action when the threads of the mating part become engaged. The two-way reversible lock nut is designed for use with machine screws and low-carbon bolts, and allows for automatic assembly because the top and bottom of the locking nut are the same. The nut will create a locking action even without being fully threaded onto its mating screw. Two-way reversible lock nuts will withstand higher temperatures than nylon insert lock nuts (nyloc nuts).

Access to the carb mounting nuts, particularly on Stromberg carbs, is very tricky so using reversible locknuts does make sense ... to me at least !

The markings are different on what's sold now but these are nearly 50 years old so things may have changed!
2 way reversible locknut with distorted thread.png
2 way reversible locknut with distorted thread.png (35.84 KiB) Viewed 530 times


Anyone else have them on their Strombergs ?
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PostPost by: 69S4 » Sat Jul 11, 2020 5:02 pm

I've just used regular nylocs. In fact the same six regular nylocs for as far back as I can remember. I'm not sure heat is a major issue for those nuts - I've measured 50 - 55C around the carb area on a really hot day (testing temp compensators) and I'd have thought nylocs would be ok with that.
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PostPost by: oldelanman » Sat Jul 11, 2020 5:42 pm

Hi Stuart,
I'm sure nyloc nuts are fine .. not suggesting otherwise, I was just trying to identify what the markings on my originals mean and I think a reversible locknut is a likely explanation. The 6 securing the carbs have been on and off a good few times over the years and there's not much "locking" left ... I should probably replace them ... but they have never come loose yet. Do you also have nylocs holding the adaptor blocks to the head .. is the recess deep enough?
Cheers.
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PostPost by: Fredtech » Sun Jul 12, 2020 8:35 am

Roger & Stuart.

If space is a bit tight on your SU Carbs, you could consider Nylock Half-heights.

Half a dozen should be cheap-ish on Flea-bay.

https://www.ebay.co.uk/itm/UNF-ZINC-PLA ... Sw5VFWH8VP

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PostPost by: USA64 » Sun Jul 12, 2020 11:49 am

My carbs with crossover functioning get quite hot; so maybe the reason.
We are supposed to be having fun, are we not?
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PostPost by: 69S4 » Sun Jul 12, 2020 12:48 pm

oldelanman wrote:Hi Stuart,
I'm sure nyloc nuts are fine .. not suggesting otherwise, I was just trying to identify what the markings on my originals mean and I think a reversible locknut is a likely explanation. The 6 securing the carbs have been on and off a good few times over the years and there's not much "locking" left ... I should probably replace them ... but they have never come loose yet. Do you also have nylocs holding the adaptor blocks to the head .. is the recess deep enough?
Cheers.



Just regular (somewhat rusty) nuts holding the adaptor blocks on. There's enough thread sticking out past them that nylocs would have something to 'grab' onto if I changed to them but I've never had issues with them coming loose.

Out of interest and following up on an earlier thread, I measured the carb to block gap with some feeler gauges earlier - 0.043'" on top and within a couple of thou of that the rest of the way round. Now just got to take it all to bits as one of the carbs is flooding. :(
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