Fordson Model N Standard - Spark Plug Thread size

[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?

[GreenV8S]

No idea, but if you have a plug or the existing tapped hole it should be easy to measure the thread pitch with a thread gauge which will probably nail it down for you.

[E-bmw]

A few clicks in google implies that it is 7/8 SAE.

http://www.fordsonmajor.se/fordson_eng/Sparkplug/c...

SAE, of course being Unified IIRC, which is either UNF (fine - 14 tpi) or UNC (coarse - 9 tpi) obviously, I have no idea if this is true or not & you say not.

The second post down on here thinks they are 18 tpi, so that may be feasible.

http://www.yesterdaystractors.com/cgi-bin/viewit.c...

Google is your friend

Edited by E-bmw on Saturday 6th January 20:02

[Woody3]

Thanks chaps - we didn't have a guide to hand unfortunately.

We've gone for a 7/8" 18tpi tap so hopefully that will do the trick..

Thanks again!