Headlight vacuum switch on S1

[rodlittle]

Does anyone have any idea what size and thread the nut on the headlight vacuum switch is? I cant find anything that fits it
cheers
rod

[Elan45]

Rod,
Not sure of the thread, but since the know has the switch shaft and knob internal has the same hex shape as many Lucas push-pull lamp switches, the thread is probably same too. Go to an autojumble and look for switches from TR3/ TR4, early big Healey's or other cars of this period and buy a junk switch to get the nut. Someone on ebay sells a little tool to tighten the nut onto the switch.

Roger

[rodlittle]

Trouble is its not the same size as all the other switches
rod

[garyeanderson]

Hi Rod

I tried a 7/16 x 20 and it starts but only gets a quarter turn before it stops. So thats not it, I don't have any 12 mm but that would be a possible. Another guess would be BA or BSPP.
The part number for the valve is 26 B 736 with the knob being a Ford part 109E-11661-B, no other parts listed near that information so who knows what the source was.

Gary

[skelteanema]

Hmmm strange,
I would have thought that it would have been the same thread as the other switches. I have a spare vauum switch at home so will go and see. I would have thought it highly unlikely to be a metric thread in a lotus specific item such as this, so my guess would be BA as well. Interestingly on a related topic, I was trying to get some nuts for the male part of the tenax fasteners for my hood and could not get anything to fit very well. When they measured the thread and looked it up, the nut and bolt experts concluded it was BA (which are not so easy to get over this side of the world). Other thread types were a loose fit, and as this was not a high torque application, I got away with it.

[rodlittle]

Hi Gary
thanks for the part no info, I too have tried every die I have and nothing fits, its way to big for BA and its not UNF metric fine or BSF its some sort of weird electronic component thread same as on volume controls etc, guess Im going to have to turn one if I cant find a spare, not something I l;ook forward too
rod

[Elan45]

Rod,

I was going to suggest BSF as the next most logical pitch. Another old British pitch
is British cycle threads or CEI and 7/16 has the common CEI pitch of 26tpi. CEI is a unique thread form with 60 deg thread form and all the sizes from 1/4 to 1" having 26tpi. I found it many years ago since it was used on old MG T series engine/ gearbox.

Roger

[Elan45]

Rod,

Know any old Brit motorcycle people. That's what I'd be trying next.

Roger

[rodlittle]

OK I give in Ive measured it its 7/16 x27tpi which according to google is a thread used on thin brass tubing (light fittings etc) Still doesnt find me one but at least its a start

Hey theres a 7/16 x 27 tap on ebay!! saves me setting up the lathe

rod

[rcraven]

Perhaps as you've said it is like the locking nuts on some electronic controls and you need to find some old volume control / potentiometer / panel switch nuts and try them.

[Elan45]

Rod,

If that is indeed the thread, almost any hardware store this side of the pond should have thin hex nuts in that size. If you can't find one that way, I could buy one and mail it to you. The control is out of my dash right now so I could check it easily.

Roger

[rodlittle]

Thanks Roger
You obviously have much better hardware stores than we do, I recall one in Seattle my son took me to and it was amazing, they died out here years ago.
I do have another offer but if that doesnt work out, Id like to take you up on yours, Ill let you know how it goes
thanks
rod