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Fordson Model N Standard - Spark Plug Thread size

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Woody3
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Fordson Model N Standard - Spark Plug Thread size

Post #1 by Woody3 » Sat Jan 06, 2018 6:37 pm

Does anyone know the thread size of the spark plug hole on a 1935-38 Fordson Model N Standard?

My friend needs to retap the head. He knows it's a 7/8" but not sure what type of thread - (It's not UNF as we've just tried that and it's too coarse).

Any ideas?

Cheers!

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Re: Fordson Model N Standard - Spark Plug Thread size

Post #2 by modelman093 » Sun Jan 07, 2018 12:31 am

Would that not have been tapped for an 18mm plug?


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Re: Fordson Model N Standard - Spark Plug Thread size

Post #3 by Woody3 » Sun Jan 07, 2018 7:32 pm

Think we've sorted it.

We believe it to be 7/8" SAE 18tpi thread.

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Re: Fordson Model N Standard - Spark Plug Thread size

Post #4 by FOWLER MAN » Mon Jan 08, 2018 3:24 am

Hi,
I have a Fordson N in the garage and I just checked out and measured a spare plug.
It 's 22mm metric.( Not imperial 7/8 SAE or UNF.) :thumbdown:

It's a 22 MM fine metric thread with a 1.5 mm pitch. :thumbup: That works back to roughly 17+ threads per inch. :think:
There should be no trouble finding a suitable tap.

I hope this helps.
Good luck.
Fred
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Re: Fordson Model N Standard - Spark Plug Thread size

Post #5 by essexpete » Mon Jan 08, 2018 5:47 pm

Forgive me for sticking my nose in Fred but is that a little unexpected? That is a metric thread on a pre 1945 Fordson?

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Re: Fordson Model N Standard - Spark Plug Thread size

Post #6 by modelman093 » Mon Jan 08, 2018 7:53 pm

Just read a post on the Yesterday's Tractors forum that says 1/2"BSP - really??

Then this on another post

I did a little research (a while back) on spark plugs for the Fordson Model E27N.
I found that the C4 & C5 Champion spark plugs are no longer made.
The C4 is now a Champion W16Y with absolutely no crossovers available.
The C5 is now a Champion W14 with three crossovers:
AC Delco numbers C75 or C77
Autolite numbers 3075 or 3076
Prestolite numbers 78-8 or 78-10
The thread used for these plugs is 7/8” – 18
Reach is 5/8”
Hex is 15/16”
Heat range is 6
Spark gap is 0.025” for all plugs.


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Re: Fordson Model N Standard - Spark Plug Thread size

Post #7 by Jeremy Rowland » Mon Jan 08, 2018 9:55 pm

essexpete wrote:Forgive me for sticking my nose in Fred but is that a little unexpected? That is a metric thread on a pre 1945 Fordson?



Yes I thought that was rather unusual? Perhaps a non-standard repair? Fred?

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Re: Fordson Model N Standard - Spark Plug Thread size

Post #8 by hair bear » Mon Jan 08, 2018 11:14 pm

Has it been helicoiled?

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Re: Fordson Model N Standard - Spark Plug Thread size

Post #9 by FOWLER MAN » Tue Jan 09, 2018 1:24 am

essexpete wrote:Forgive me for sticking my nose in Fred but is that a little unexpected? That is a metric thread on a pre 1945 Fordson?


Hi,
I'm sure every other thread in the Fordson is SAE, but most plugs had gone metric pre-war.
I checked my plug with a Micrometer and Thread Guage.

Here is a Fordson N plug from the Old 20 Parts List.
Image


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Re: Fordson Model N Standard - Spark Plug Thread size

Post #10 by Jeremy Rowland » Tue Jan 09, 2018 8:25 am

FOWLER MAN wrote:
essexpete wrote:Forgive me for sticking my nose in Fred but is that a little unexpected? That is a metric thread on a pre 1945 Fordson?


Hi,
I'm sure every other thread in the Fordson is SAE, but most plugs had gone metric pre-war.
I checked my plug with a Micrometer and Thread Guage.

Here is a Fordson N plug from the Old 20 Parts List.
Image



How very interesting Fred I never realised that metric plugs were around so early; coincidently that is how I check unknown threads at work with a micrometer and a thread gauge plus a Zeus book that lists all the threads and what TPI or pitch they should be. :thumbup:

Jeremy


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