Cylinder head brass plug

I've just fitted this 12J engine to my Series 2A.
Can anyone please tell me the thread form/size on this brass plug that fits in the rear upper face of the head.
The engine was ex military originally, the early 12J type.
Unfortunately, while I have series parts catalogues, I've got nothing for 90/110.
Thread diameter is approximately 21mm

Most likeley 1/2 inch bsp, same as the radiators in your house, so plumbers merchant will have what you need.

Hope this helps

lynall said:

Hope this helps

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Many thanks !
It did look like BSP to me at first glance, but I thought no, that would be too simple

grewth said:

Many thanks !
It did look like BSP to me at first glance, but I thought no, that would be too simple

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Iirc later units went metric, maybe in 89 as per the parts sheet.

lynall said:

Iirc later units went metric, maybe in 89 as per the parts sheet.

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Lots of things changed, and for no apparent good reason.
I bought a set of main bearing shells from Paddocks, only the top (block) ones fitted, the lowers were tabbed in the wrong place.
Only then I found out that the early engines are different

Hmmmm.........Just been trawling eBay for BSP plugs, the sizes seem to go from 3/4" to 1" with nothing in between, and my plug measures about 21mm across the outside of the threads.

What’s wrong with the 1 you have?

J

Grebby said:

BSP Thread Sizes Explained

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Many thanks for that.
It's been many years since I had any dealings with pipework.
I spent about nine months welding sprinkler sockets onto steel pipe, but that was about thirty years ago, I've almost forgotten anything I learned.

marjon said:

What’s wrong with the 1 you have?

J

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Well, I had months to sort this problem out before fitting this engine to my vehicle, but of course I completely forgot about it.
Just behind the hole with the brass plug is another hole, a good bit smaller, this is for the heater circuit brass stub.
LR used a very fine thread for some reason and this was completely stripped.
So I somehow managed to bodge the temp gauge sensor in that hole, helped by some RTV sealant. Not good engineering I admit, but I was desperate to get a drivable vehicle.
So having fitted the temp sender into a hole it wasn't intended for, I now need a fitting for the heater circuit.
Planning to replace the brass plug with something with a 1/2" outlet