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MG Midget and Sprite Technical - 1275 Engine block. Water drain plug. Thread?

Does anyone know the thread of the water drain plug in the side of the block? -- I've lost one.

Part number 53K2853

I can buy a plug on ebay, but I don't fancy paying 10 quid(inc post) for a simple bolt.

Or 6.20 inc vat, but plus 4 quid post from Moss.

It's a parallel thread, so I'd rather just buy a bolt, if I know the thread.

Lawrence Slater

It appears to use the same washer as the sump plug, so likely 1/2" UNF.

You could maybe use a spare temperature sender, if you have one - assuming there is enough clearance.
Dave O'Neill 2

I think it could be 1/4 BSP

You could use an original tap as seen on Morri Minors etc.

If the bolt in the pic is what you need (same thread as the tap) drop me your address (I think you have my e mail) and I'll pop it in a jiffy bag.
I don't have any copper rings - they should be available locally - seem to remember they were plain flat copper - not as your pic.

Could put the crank in a bigger bag !


richard boobier

Good thinking Dave. I've got a few temp senders, I'll check.

I'll also test the sump drain for fit too. That's only 2.91 from some places.
Lawrence Slater

Hi Richard,

I'll check Dave's suggestions first, and let you know.

I've re-used my old crank with some new shells for this engine. Jounals were fine. I'll take the midget engine out in the next week or so, and inspect the crank in that. If it's suspect at all, I may well have your crank, as then I'll be able to sell the car with a "new" crank and shells. Won't put any more money on it, other than the price of your crank, but will add to saleability.


Had one of those taps years ago, it went missing. I suspect that's what I've actually mislaid, as this engine has been off the road since circa 1998.
Lawrence Slater

Its not a "new" crank only a Moss Recon.

If it is BSP a plumbing fitting should fit.

richard boobier

Hi Richard,

Yup, I meant a recon crank, but done properly, that's as good as new to me. :).

The sump drain plug definitely fits, and the sump drain plug fits an old gas fire fitting too. So as you say, it's a 1/4" bspp fitting.

I can get a brass or steel one on Ebay for 1.85/6 inc post. But I'll nip to my local plumbing store (5 min walk) and get one on Monday.

What I can't understand, is how the 1/4" measurement is derived, as it measures o/d 1/2".
Lawrence Slater

Sussex sell the sump plug 88G257, for 1.56 inc vat.

So do Moss.

So what's the difference between Moss's 53K2853 6.20 inc vat, engine block drain plug, and Moss's "DRAIN PLUG, sump" 88G257, 1.55 inc vat, -- Apart from the part number, and the price?

Lawrence Slater

Sump plug, in a gas fitting.

Lawrence Slater

The 1/4 " relates to the bore size of a pipe in 'plumbing speak'

1/4 BSP and UNF 1/2" are quite close - ish - especially when viewed over a short thread length and may fit (sort of ) so perhaps the part numbers relate to different threads ?

richard boobier

Just checked and the temp sender is the same pitch, but larger diameter - 5/8"

One difference between the sump plug and the block drain plug is the size of the hex.
Dave O'Neill 2

There must have been a difference that made it worthy of 2 part numbers, if not the price.

But I'll see what the local plumbing shop has. I don't really care as long as it screws in easy, and doesn't leak. :).
Lawrence Slater

Besides the thread size, what size spanner fits that plug? I tried to get mine out (with engine in car) for a good flush and could not get a good fit using SAE or metric to get a good grip on it. Is it Whitworth? It may just be that it hasn't been out in so long that it may take more than just a wrench!
Jack Orkin

Definitely shouldn't be metric.
Lawrence Slater

3/8 Whit spanner fits IIRC
Dave O'Neill 2

Whitworth may be a bit oddball these days but fine when it was standardised just not that common now in most sectors. I found a nut on the table clamp of my Chinese pillar drill circa 2000, needed to angle the table from horizontal, was only fitted well by a Whitworth ring spanner which I borrowed from a neighbour. There wasn't room to fit an adjustable or open end spanner, it had to be a ring spanner, and no standard inch or metric spanner fitted the nut well enough to do the job, I have a full range from below to above the size required, so went next door and borrowed the Whitworth, job done. I've heard of the Chinese doing that before when buying the tooling and using it long after the sizes fell from favour.
David Billington

1/4" BSP has an O/D of 0.518" with 19 TPI and a 55 thread angle.

1/2" UNF has an O/D of 0.500" with 20 TPI and a 60 thread angle.

Both use the same size tapping drill at 11.50mm so choose wisely.
Martyn Wilks

I don't need to drill and tap a thread Martyn, only buy a cheap bolt that fits. And now I know it's 1/4" BSPP, problem solved.
Lawrence Slater

Doug Plumb found that Minispares sell the plug, and confirm it's 1/4" bsp
DRAIN PLUG ENGINE BLOCK REAR WATER DRAIN OFF 53K2853 4.65 ex vat 5.58 in vat
Lawrence Slater

Yup definitely 3/8WW for the engine block plug, and 3/4AF for the sump plug.

I guess there must have been a reason for that, but I can't think what.
Lawrence Slater

I guess because the sump plug is probably UNF and the drain BSP. I have several Whitworth spanners that fit various plumbing fittings so I think they are probably standard fitment for BSP.

Trevor Mason

Nope, that's exactly the point Trev. They are BOTH 1/4" BSPP.

So why the different spanner size?
Lawrence Slater

Some BSPP fittings have larger hex sizes because they are intended to accommodate Dowty seals (or copper washers) when screwed into a machined surface like the side of a valve pack for example. That's where they need the bigger surface under the hex.
Some have smaller hex sizes where the intended seal is against the taper inside the bore of the fitting - for example when it has a hose-end screwed onto it. A BSPP hose end has a male taper profile to match and needs no other seal.

Well anyway, problem solved.

I bought a brass 14"bspp plug from my local plumbing merchant, for the total sum of 1.00. Bargain. So much cheaper than, and just as good as, the 'real thing'.

It has a flat collar, and I had a spare copper washer that fits perfectly.

The only compromise(if it is), is that the hex head is metric. 14mm. I can live with that. :).
Lawrence Slater

9/16" should fit
Martyn Wilks

Just got my King Dick 3/8 - 7/16 W spanner from ebay! Looks like 3/8 W it is. Now, I just hope that when I'm ready to remove that plug for a good flush I'll be able to find the wrench!
Jack Orkin

This thread was discussed between 02/01/2016 and 08/01/2016

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