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Fordson Model N Standard - Spark Plug Thread size
Posted: Sat Jan 06, 2018 6:37 pm
by Woody3
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!
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Sun Jan 07, 2018 12:31 am
by modelman093
Would that not have been tapped for an 18mm plug?
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Sun Jan 07, 2018 7:32 pm
by Woody3
Think we've sorted it.
We believe it to be 7/8" SAE 18tpi thread.
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Mon Jan 08, 2018 3:24 am
by FOWLER MAN
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.)
It's a 22 MM fine metric thread with a 1.5 mm pitch.
That works back to roughly 17+ threads per inch.
There should be no trouble finding a suitable tap.
I hope this helps.
Good luck.
Fred
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Mon Jan 08, 2018 5:47 pm
by essexpete
Forgive me for sticking my nose in Fred but is that a little unexpected? That is a metric thread on a pre 1945 Fordson?
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Mon Jan 08, 2018 7:53 pm
by modelman093
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.
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Mon Jan 08, 2018 9:55 pm
by Jeremy Rowland
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?
Jeremy
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Mon Jan 08, 2018 11:14 pm
by hair bear
Has it been helicoiled?
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Tue Jan 09, 2018 1:24 am
by FOWLER MAN
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.
Re: Fordson Model N Standard - Spark Plug Thread size
Posted: Tue Jan 09, 2018 8:25 am
by Jeremy Rowland
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.
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.
Jeremy