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  • July 26, 2021, 08:27:00 AM

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Author Topic: OS NVA THREADS  (Read 861 times)

Offline Tom McClain

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OS NVA THREADS
« on: June 04, 2021, 02:50:15 PM »
Anyone got a clue on what threads are used for OS RC NVAs? It is not English or metric.
Tom McClain

Offline BYU

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Re: OS NVA THREADS
« Reply #1 on: June 04, 2021, 08:26:08 PM »
The thread is M3.5 if I am not mistaken. At least it is on the control line needle valve assembly.



Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #2 on: June 04, 2021, 11:38:01 PM »
Anyone got a clue on what threads are used for OS RC NVAs? It is not English or metric.

Tom, the thread on the 0.S. r/c carb needle as well as the remote needle on LA 40 etc is indeed metric and is m4 x 0.5 .  Taps and dies are readily available........ but guess where from!!

DH
« Last Edit: June 05, 2021, 02:16:04 AM by Dallas Hanna »

Offline Tom McClain

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Re: OS NVA THREADS
« Reply #3 on: June 05, 2021, 07:24:51 AM »
The thread I am looking for is for the assembly housing that goes in the Venturi not the needle.  Thanks.
Tom McClain

Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #4 on: June 05, 2021, 05:04:41 PM »
The thread I am looking for is for the assembly housing that goes in the Venturi not the needle.  Thanks.

Can you give us a better clue on which screw is it then Tom.  Can you supply a photo or sketch?

D

Offline Dan McEntee

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Re: OS NVA THREADS
« Reply #5 on: June 05, 2021, 05:49:57 PM »
The thread I am looking for is for the assembly housing that goes in the Venturi not the needle.  Thanks.

    I think he means the external thread on the spray bar. I think that should be a 4mm by .5mm. As mentioned it is the same thread as the NVA that screws into the older OS carbs. I have used those for spigot venturis and I'm pretty sure that is what I tapped the venturi for. .
   Now that I typed all of that. I'm thinking that we should be asking which vintage OS NVA?? If it's the early version that would come with a black and white header card, those were a bit larger. The last generation of the OS NVA for the .20 through .46 is smaller. The dimensions escape me right now. Mic the spray bar diameter in thousandths and let us know.
  Type at you later,
   Dan McEntee
AMA 28784
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AMA 480405 (American Motorcyclist Association)

Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #6 on: June 05, 2021, 07:16:08 PM »
Tom, if it is the thread which the NVA screws into the body of the RC carb, the smaller 2A carbs use the m4 x 0.5 thread.  If it is the larger 4D-7D carbs, it looks like OS used 1/4"-32 UNEF thread. Pics for ref.  Hope this is what you are after.

Offline Tom McClain

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Re: OS NVA THREADS
« Reply #7 on: June 05, 2021, 07:44:53 PM »
This is a later more modern RC NVA that I want to use for sprinkler type ventures. I will provide a picture of it soon.
Tom McClain

Online Brett Buck

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Re: OS NVA THREADS
« Reply #8 on: June 05, 2021, 08:25:19 PM »
If it is the larger 4D-7D carbs, it looks like OS used 1/4"-32 UNEF thread.

   Oh my!  I was unaware until fairly recently that this is a common British modeling (as in steam engines, etc) thread, but that OS uses it seems nuts.

    Brett

Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #9 on: June 06, 2021, 12:03:05 AM »
   Oh my!  I was unaware until fairly recently that this is a common British modeling (as in steam engines, etc) thread, but that OS uses it seems nuts.

    Brett

The 1/4"-32 used on the glow plugs is your (USA) Unified thread Brett.  Some of the Poms thought it was their M.E thread until convinced that the thread angle was 60 deg, not their 55 deg on the glow plugs.  When I went looking at the three OS carbs earlier I thought surely they used a fine series m6 thread.  On measuring with the shadowgraph for pitch it was looking like 32 tpi with an o.d two whiskers under 0.250".  I then checked the internal thread with a 1/4" UNEF tap which seemed to varify the use of an imperial thread.  Also remember that OS went Unified on the crankshaft threads as well very early on.

D

Offline Tom McClain

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Re: OS NVA THREADS
« Reply #10 on: June 06, 2021, 02:26:22 PM »
Here are the parts in question.  Super Tigre 51Venturi and OS NVA.
Tom McClain

Online Brett Buck

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Re: OS NVA THREADS
« Reply #11 on: June 06, 2021, 02:33:25 PM »
The 1/4"-32 used on the glow plugs is your (USA) Unified thread Brett. 

   I know that - but it's so rare as to be nearly unique, never used for anything, aside from being a glow plug/spark plug thread. There are also defines UNxx sizes 12-24, 4-48, etc. but you don't see those, either. I was just surprised to see people using it on British steam engine kits.

     Brett

Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #12 on: June 06, 2021, 05:35:02 PM »
Here are the parts in question.  Super Tigre 51Venturi and OS NVA.

Looking at your NVA Tom, it looks more like an Enya brand.  I've added a pic for you to compare inlet nipple.   Small Enyas (09) used m4 x 0.5 and larger Enyas (I only have 40 and 45 size to check) used m5 x 0.8 thread which screws into the carb body.  What diameter is the thread you have which will screw into Venturi?

D
« Last Edit: June 06, 2021, 06:02:25 PM by Dallas Hanna »

Offline Tom McClain

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Re: OS NVA THREADS
« Reply #13 on: June 06, 2021, 07:33:39 PM »
.194
Tom McClain

Offline Dallas Hanna

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Re: OS NVA THREADS
« Reply #14 on: June 06, 2021, 08:59:15 PM »

Offline Tom McClain

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Re: OS NVA THREADS
« Reply #15 on: June 06, 2021, 09:08:12 PM »
m5 x 0.8 is your thread Tom.

D

Thanks!
Tom McClain

Offline Mike Greb

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Re: OS NVA THREADS
« Reply #16 on: June 14, 2021, 04:37:28 PM »
I set up one of the larger os carbs for a remote needle valve, used a glow plug to plug up the hole were the needle valve went, so it is pretty close to 1/4-32


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