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Old 08-09-2020, 12:06 PM   #1
johnbuckley
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Default GAV needle threads... unique to this component?

Just interested ...The thread on the GAv needle and inside the housing seems to be a real odd ball...According to Model-A.org the threads are 1/4-24. This thread is virtually unknown in UK ... is this thread used much in the states?
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Old 08-09-2020, 12:31 PM   #2
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Default Re: GAV needle threads... unique to this component?

Outside of the Zenith Model A or Model B carb, I have yet to come across any 1/4-24 threads. The matching tap and die sets are available, however.
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Old 08-09-2020, 12:31 PM   #3
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Default Re: GAV needle threads... unique to this component?

It is not a very common thread pitch in the US.

I just looked online and McMaster-Carr sells a 1/4-24 tap for about 25 USD. So they are out there.

You can thank the French at Zenith for this odd thread.
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Old 08-09-2020, 04:50 PM   #4
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Default Re: GAV needle threads... unique to this component?

I am just dealing with this now. We are rebuilding some model B carbs. The GAV
Is 1/4-24 and we need a 1/4 24 bolt for a puller to remove the GAV.

Model T magnet bolts are 1/4-24 ,but they are brass. I am going to cut the threads on my lathe for a steel puller bolt.

We got the plans for the puller from Renners Corner,they are great to deal with for model B carb information and parts.

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Old 08-09-2020, 05:03 PM   #5
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Default Re: GAV needle threads... unique to this component?

Isn't it odd that they would use both standard and metric threads on a Zenith. I'm sure there is an old dead engineer someplace laughin' his ass off.
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Old 08-09-2020, 05:17 PM   #6
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Default Re: GAV needle threads... unique to this component?

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Unified National Special sizes are the uncommon sizes that are difficult to find information about. The UNC and UNF sizes are common but UNS is not so much. The first time I ran into UNS was working on older Harley Davidson motorcycles. They used a lot of UNS sizes. It forced folks to purchase their fasteners from the dealer network for the most part. I had to purchase UNS taps, dies, and heli-coils while performing restorations on these machines. Reproduction fasteners are available too but I like to reuse as much of the original stuff as I can on some restorations.
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Old 08-09-2020, 07:02 PM   #7
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Default Re: GAV needle threads... unique to this component?

1/4 X 24 tpi is not even close to a metric thread.
1/4" is 6.035mm so not 6 mm
24 tpi is a pitch of 1.06 mm not a fit there either.
6mm Metric coarse has a pitch of 1.0 mm.
1/4" Brass is 26 tpi
1/4 UNF is 28 tpi.
It seems to me that 1/4" X 24 is a real oddball. It's not even BA
All that said, I don't understand the American "gauge" threads. I'd never heard of them till I started playing with Model As. Does it fit one of those?
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Old 08-10-2020, 12:34 AM   #8
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Default Re: GAV needle threads... unique to this component?

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1/4 X 24 tpi is not even close to a metric thread.
Nobody said it was?
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Old 08-10-2020, 03:47 AM   #9
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Default Re: GAV needle threads... unique to this component?

thanks everyone .. I guess it's part of the fun of old cars

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Old 08-10-2020, 03:59 AM   #10
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Default Re: GAV needle threads... unique to this component?

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Nobody said it was?
POst #5 "Isn't it odd that they would use both standard and metric threads on a Zenith. I'm sure there is an old dead engineer someplace laughin' his ass off."
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Old 08-10-2020, 06:16 AM   #11
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Default Re: GAV needle threads... unique to this component?

As other threads in the zenith are metric, could it be a 6mm x 1mm pitch thread. That would be very close to a 1/4" x 24 tpi. I would try a metric bolt or tap of that measurement first.
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Old 08-10-2020, 07:06 AM   #12
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Default Re: GAV needle threads... unique to this component?

M6-1 is close but doesn't fit -I've tried it. close but no cigar . Though of course one could retap and die things to whatever you like if push came to shove

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Old 08-10-2020, 07:09 AM   #13
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Default Re: GAV needle threads... unique to this component?

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As other threads in the zenith are metric, could it be a 6mm x 1mm pitch thread. That would be very close to a 1/4" x 24 tpi. I would try a metric bolt or tap of that measurement first.
Yes, this is possible. I think someone needs to look at a copy of the original engineering drawings for the carb to see what is called for there. Does anyone have a copy of those drawings? Is anyone going to the Benson Ford Archives any time soon?

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Old 08-10-2020, 08:52 AM   #14
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Default Re: GAV needle threads... unique to this component?

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Old 08-10-2020, 09:31 AM   #15
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Default Re: GAV needle threads... unique to this component?

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Originally Posted by Synchro909 View Post
POst #5 "Isn't it odd that they would use both standard and metric threads on a Zenith. I'm sure there is an old dead engineer someplace laughin' his ass off."
They used the " X 24 thread GAV but they also used metric threads in the Zenith, for example 5mm X .75 Compensator jet. I never said the " X 24 was the equivalent of a 6mm X 1.

I was pointing out that I thought it was odd that they use "both standard and metric threads on a Zenith".
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Old 08-10-2020, 09:39 AM   #16
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Default Re: GAV needle threads... unique to this component?

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Originally Posted by Jim/GA View Post
Yes, this is possible. I think someone needs to look at a copy of the original engineering drawings for the carb to see what is called for there. Does anyone have a copy of those drawings? Is anyone going to the Benson Ford Archives any time soon?

Jim, would the Zenith drawings be at Benson Ford Archives since the Zenith carb was made by an outside source and not Ford? Something like Houdaille Shock?
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Old 08-10-2020, 09:51 AM   #17
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Default Re: GAV needle threads... unique to this component?

Are you sure that they're not #14-24?
Sometimes people mistake #14 for 1/4".
14-24 is an old ASME thread.
#14 is .242" diameter.
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Old 08-10-2020, 10:31 AM   #18
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Default Re: GAV needle threads... unique to this component?

Picking up on what Katy said ...the now obsolete ASME thread standards had number size screws from # 2 (.0842) to #30 (.4526) with many optional thread pitches. Unfortunately there were several sizes that are deceivingly close to the common "inch" sizes. Three of the worst that can cause BIG trouble are #12 (.216), #14 (.242), and #16 (.268) , these came in pitches , 16, 18 , 20 , and 24 tpi.

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Old 08-10-2020, 11:12 AM   #19
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Default Re: GAV needle threads... unique to this component?

Quote:
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Jim, would the Zenith drawings be at Benson Ford Archives since the Zenith carb was made by an outside source and not Ford? Something like Houdaille Shock?
I don't know if the drawings will be in the Archives or not.

Over time the carbs were manufactured by Zenith, Holly, and Ford. I would expect to find a drawing there somewhere.

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Old 08-10-2020, 11:33 AM   #20
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Default Re: GAV needle threads... unique to this component?

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I don't know if the drawings will be in the Archives or not.

Over time the carbs were manufactured by Zenith, Holly, and Ford. I would expect to find a drawing there somewhere.

Thanks Jim, just curious. I have never been to the Archives.
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