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MG Midget and Sprite Technical - Brass Filler Plug

I have just changed the plastic filler plug on my 77 1500 for a brass one. The plastic one got a bit burred the other week when I tried to remove it. On fitting the brass plug with the rubber washer, the washer squeezes out unevenly. I loosened it off & tried doing it up to get the washer to seal evenly - to no avail. I ran the engine for a few minutes and surprise suprise it started weeping. Anyone had experience of these brass plugs & fitting them. Do they need anything like PTFE for example. At the moment, I'm not impressed and may put the plastic one back as it works, albeit the nut bit slightly burred.
Nigel Axtell

Yeah... Id definatly use some ptfe paste, anytime im using metal parts that hold water... I always use ptfe paste...the tape works good but i just perfer the paste, its so trouble free...

Prop and the Blackhole Midget

I don't think the problem lies with the brass plug, rather with the O-ring. My plastic plug causes the O-ring to distort and squeeze out of shape, too. I believe the answer lies in using an O-ring with a smaller internal diameter so that it is less inclined to squeeze out of shape. And/or one could try using an O-ring made of firmer material (nitrile? neoprene?).
Andy Hock

I've a brass plug in the crossflow rad in my frogeye and it just has an 1/8" section O ring seal and works fine without any sealer. It only needs to be nipped up to seal but would extrude out if overtightened. Sealer shouldn't be required.
David Billington

Those flat, translucent neoprene washers for plumbing use - used for seating bath taps - work well. The early originals used a flat washer made of the pink stuff that looks a bit like linoleum.
Guy W

I'm speaking from personal experience now - don't overtighten the O-ring

for the earlier cars some (one?) has said only the plug is required, others use a washer, you could try Prop's idea

but a replacement O-ring will work
Nigel Atkins

I'd try to find the fibre O ring I think Guy is talking about, looks like linoleum.

Plumbing merchants can usually supply if the local car spares chap has run out.

They squash up well without distorting and as David and Nigel say you don't need to squeeze the joint down hard.

Guy is spot-on as usual, plastic or fibre washer with the brass plug...
David Smith

or just don't tighten it very much... it only needs to be hand tight. I pinch mine up using a socket without a bar or arm, just finger tight. Even though my o ring is deteriorated - it doesn't leak.
C L Carter

I've got a brass plug and no washer whatso ever. Never had a problem and the car runs cool. Maybee the plug and radiator have 'lapped' together over the years.
Chris H (1970 Midget 1275)

I ordered one of these brass plugs and when it arrived knew there would be problems as there is not a recess in the plug face to locate the o ring and keep it in position while tightening.

I asked a pal with a lathe to run a suitable shallow groove in the face of the plug and the o ring stays put now.
I would have done it myself but since retiring I do not have access to a workshop.

I doubt if it would cost much to have a machine shop do it for you.
The brass plug is much better than the plastic one, but only if it has an o ring location groove, in my opinion.
JB Anderson

JB Anderson,

Mine doesn't have a recess for the O ring and it is an original OEM item and seals fine if just nipped down. I have the machining facilities to cut a better groove for the O ring but have never found a need too.
David Billington

Thats fine David, but as an engineer in the aero engine industry I came to expect some sort of locating groove for an o ring.
I realise a midget is hardly the same thing but I was able to get a groove in my plug so I had it done.
I was just not happy with the way the ring wanted to deform and try to escape from under the plug even with just "nipping up".
If you are successful with yours then alls well for us both!
JB Anderson

JB - you are using mismatched parts. The brass plug is to be used with a flat washer, either fibre or plastic/nylon, as originally supplied by the manufacturer. The black plastic screw plugs are used with the rubber O-ring. I note that Moss catalogue only lists Brass plug and O-ring, which is an incorrect pairing; they add to their own confusion by using a non-original part no. for the brass plug, the correct one being ARA2404.
David Smith

The brass filler plugs were never designed or intended to be used with a modern O ring - so its not surprising that there is no machined groove. Its not a mistake, or sub standard part!
Guy W

I would have used a washer had I the right size in my washer box but I didn't so same as David I've an o-ring just nipped up (very important it's not overtighten with the o-ring as I found, it also cost me two paint runs but that's another story)
Nigel Atkins

JB Anderson,

I understand that feeling as I'm an engineer also but in the case of the spridget brass rad plug the O ring is more than sufficient if nipped up and not overtightened so it extrudes out from under the plug. I expect a better solution is a more solid washer type seal or a Dowty washer but over the top for what is required.
David Billington

I've had countless Spridgets with crossflow radiators, fitted with the brass plug and none of them have had O-rings or washers. No leaks, either.
Dave O'Neill2

Dave, thanks for that info. I was begining to think I had dreamt it when I said I have no washer of any type and no problems. You just confirmed I'm not going mad.
Chris H (1970 Midget 1275)

quote "JB - you are using mismatched parts. The brass plug is to be used with a flat washer, either fibre or plastic/nylon, as originally supplied by the manufacturer. The black plastic screw plugs are used with the rubber O-ring. I note that Moss catalogue only lists Brass plug and O-ring, which is an incorrect pairing; they add to their own confusion by using a non-original part no. for the brass plug, the correct one being ARA2404. "

Thanks for that David, that makes a lot of sense.

There must be a lot of potentially leaky plugs out there by owners trying to seal a flat surface with an o ring with no location, by hopefully not overtightening and deforming it.
I certainly wouldn't be happy with that situation.

Some of these parts suppliers should be shot,for not selling the correct matching parts.
For those without a bit of mechanical nouse it must be a nightmare.

JB Anderson

I don't think an on 'O' ring is ever going to work with a brass plug. Its a very loose fit over the threaded part and is going to get mis-shaped as soon as its tightened. I also noticed that the threaded part of the brass plug is longer than the plastic one - whether that makes any difference. I tried the washers from the plastic plug - 2 x what appear to be aluminium. They are better than the 'O' ring but it still weeps a bit when its warmed up. Maybe fibre washers are a better option.
Nigel Axtell

Plumbers have been using fibre washers for water sealing for a very long time.

For hot and cold systems, they rarely fail until they've been loosened from a properly seated condition then retightened.

I would advise only fibre if using brass.

If the brass screw has a thread that allows closing right up to another brass boss you may not even need a washer, they are often self sealing - brass to brass.

O-rings will and can be rused when plug is removed I know as I've taken the plug out several times and reused the same O-ring several times - just don't overtigten

if I find a few fibre washers of the correct size I'd use them in preference but I not looking at the moment, if the o-ring went I'd just try fitting without washer or O-ring to at least get me home and if it worked I'd leave as is
Nigel Atkins

I must admit to being somewhat puzzled by all this. The brass plug is designed to be used with a fibre washer, so why not use a fibre washer - they are readily available (and look better!) I am sure they will seal with a modern O ring, if not overtightened, but what's the advantage?
Guy W

if it's to hand and you don't have to go search all over town searching for the correct size washers - done that for the washer for the shower

only to find I had what I wanted in my box of washers but somehow managed to miss them, I paid for my mitake by having to also go into a large B&Q as well as the local plumping stores
Nigel Atkins

I do sometimes wonder....
David Smith

errrr, the o-ring works, it's an alternative - I hope this admission wont cost me points at the next concourse event

I think my mate has a genuine flat washer, it's just split, if I can be told the original factory glue I could repair it and use it for judging purposes :)
Nigel Atkins

......I paid for my mitake by having to also go into a large B&Q as well as the local plumping stores.....

Tell us more about these plumping stores, I'm intrigued :-)

I Ball

yes I noticed that mistake too late, originally I put plumming and realised my mistake so put a p in for some reason

what about my other 'mistake'

there are plumping stores but they're in another part of town :)
Nigel Atkins

No mention of washer OR O-ring in BL parts book...

Nor in the driver's handbook, I hasten to add ;o)

Dave O'Neill2

Dave I think that's because the plastic washer was not supplied as a separate part -it was actually fitted to the plug at the time of manufacture. The hole in the washer is smaller than the OD of the thread, it may have been screwed on or fitted by a machine, possibly after heating for pliability. You can just about see it in this pic, which is of a genuine original used item I've had in store for years.

David Smith


you're right. The washer on mine has failed. There didn't appear to be a direct replacement as it was made from a nylon type material with 'ears' on the inner.
However Triumph Stags use the same brass plug ARA2404 and have a sealing ring ARA987.
There's a pdf showing the two parts at
The seal is available from LD Part for 1.47 (but with a 4.80 p&p cost) and has the 'ears' but the photo makes it look as though it may be made from a different material than original.


Jeremy 3

This thread was discussed between 15/09/2012 and 22/09/2012

MG Midget and Sprite Technical index

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