Douglas SV54

And use a very close fitting spanner as the nut willl collapse, because its quite thin, if the spanner is loose fitting.

Maryalice

Thanks for the info re spark plug, but it looks pretty ratty so I think I'll splash out a few quid on a new one.

Another question.
Where can I get the nut that holds the HT lead to the magneto terminal?

Paul,
A rotary wire brush may just surprise you, what have you got to loose, I've used worst looking plugs in my Listers.

Maryalice

You can get the nut that holds the HT to the mag from the same place you get the plug....

www.gsparkplug.com

As for the plug looking ratty, I could probably say it would work better than a new one. But I won't.....

Villiers wrote:You can get the nut that holds the HT to the mag from the same place you get the plug....

Had a look on Green Spark plug but couldn't find the nut

Woodsman wrote:

Villiers wrote:You can get the nut that holds the HT to the mag from the same place you get the plug....

Had a look on Green Spark plug but couldn't find the nut

https://www.gsparkplug.com/ignition/spark-plug-accessories?p=2

Pete.

Hi Pete,

I guess you mean 'Spark Plug Brass Thumb Nut' - any idea which thread?

Be careful there are two types of thread, I dont know the actual types but I know from experience they are different.

Maryalice

Actually three types of thread were/are used for spark plug thumb nuts, 2BA, M4 and 8/32 UNC.

Another piece of useful information

Isn't 8/32 actually 1/4.....

I missed that one, well spotted.

Villiers wrote:Isn't 8/32 actually 1/4.....

NO !!! Not in this case.

8 is the UNC fractional size (about 0.164 inches diameter)  and 32 is the number of threads per inch.

1/4 UNC is 0.25 inch diameter and 20 threads per inch,  and therefore quite different to 8/32 UNC.

Blue Cat,
Another thing I've learnt this week, I loocked at my thread charts to find it, the threads go down to 2/56, I always thought that UNC started at 1/4 my Zeus doesnt show below that.

Martin P

The threads go down to 1/64 UNC (or at least they did in 1941 which is the date of my thread charts).

Fractional size 1 (diameter 0.073 inches) with 64 threads per inch.

My Zues is approx 10 years old, not shown, My Engineers Precision Data is 6 years old and American it shows down to 2, yet to check my Kemps or 70's Machinery's

Maryalice

Well I stand corrected and will bow to Phillips superior knowledge....

So I did my best to measure the diameter of the magneto HT terminal - a tad tricky getting the calipers in. As far as I can see it's around 0.156" or approx 4mm. I believe that rules out 2BA but could be Number 8 UNC or 4mm.
Struggled to get the thread gauge in yesterday so will have another go today.

'ang on Paul, do you mean the retaining thumb screw that holds the HT ti the mag cap?

It's listed here.....

http://www.villiersparts.co.uk/wip.html

#16-463 And only £2.95! Even a tight Yorkshire man can afford that!!

Ah ha, I thought he meant the plug terminal thread as well!

Pete.

Villiers wrote:You can get the nut that holds the HT to the mag from the same place you get the plug....

Pay attention you two

But thanks for the link  - will order same on Monday.
After cleaning up the plug a little I may give it a go (though the terminal doesn't screw completely into the porcelain)
How you supposed to gap these two pronged jobbies?

You gap the 2 prong plugs by gapping one side at a time.....

Just joined this forum and this post caught my eye as i have a Douglas SV 54 that i picked up on ebay a few years ago  for my 1947 trusty 2 wheel tractor. Mine is fitted with an SU carb and was bought as a non runner.....turned out to be a worn pin where the starter handle goes in ...the starter handle couldn't grip it.  Its a great starter with the su carb...i am no fan of amal carbs. The original fuel tanks are also prone to leaking.

The Trusty looks a bit of a beast - please post a couple of pictures when you are able.