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MG MGB Technical - Welch plug in block drain hole?

As part of what I thought was routine water flushing today, I removed the drain plug down in the block near the distributor. I had drained coolant from the bottom hose before removing the heater valve ( because of the usual failure), and put in a blanking plate. To my amazement, when I extracted the little drain plug, no coolant came out of the block. So I got my little mirror on a stick - and lo and behold, what appears to be a little welch plug or similar, inserted into the drain hole! Very hard to photograph, but you might just be able to see it.
I'm wondering why on earth this drain plug would be deliberately blocked off.
BUT - this is my 'UK built 73 BGT with a DBL 230 ... (etc) engine number, of which only a small number have been identified to date; something like 2 in the US, a couple in the UK and maybe 1 or 2 here in Australia. These blocks were discussed back in 2016 ( in the archives as "BGT Engine number origin?"), and one school of thought was that the blocks were purloined by Leyland around '73 to be used in MGB production having originally been intended for Leyland (non-MG)vehicles, and even to be marinised for boat use. Could any of that background explain the blocking off of the drain plug??
All thoughts appreciated. John.


J P Hall

It seems to be considered unusual to get coolant out of the drain by the distributor but for reasons of being blocked with casting sand, I've not managed to get more than a seep out of mine.

The only thing that comes to mind with that inner plug is if the thread for the original had 'worn out'. I've had that with the lower heater valve screw (possibly because of repeated valve replacements ...) and bonded a stud into the block and used a nut and spring washer. But then they could have done that with the original plug or tap.
paulh4

Are you sure it’s a welch plug and not solidified sludge?
Dave O'Neill 2

I will second Dave's hard sludge post. We use an elongated drill to get down to the bottom of the crap via a waterway on the block face and drilling straight into the hole on the side of the block, it can take ages sometimes!
Peter Burgess Tuning

Hmm - so more sleuthing needed. It certainly looked and felt (scriber tool) like a dished welch plug, but from what you all say, it could be solid detritus, OR the drain channel at that horizontal section was never drilled through in the first place. Bizzare.
So to get the best result from flushing/back flushing, what would be the best approach, given the blocked drain hole? The upper water galley seems to flush out ok, but I'd like to somehow flush through the bottom section of water jacket as well. I'm assuming it's best to remove the thermostat and go down the housing entrance, but any other advice gratefully received.
Also : is there a standard way to isolate the heater matrix when the dreaded heater valve has been blanked off? It's 30c every day here for the next few months, so the heater is certainly not needed.
Thanks always. John.
J P Hall

Hi John -blew your pic up for a look---made it bigger is about all we learnt from that little exercise--Question-- How deep is from the outer face of the block to the suspect- and how deep is the bung.
As the guys have mentioned these blocks are prone to getting clogged up down/back there, i'm suspecting it's just solidified rubbish.
willy
William Revit

Well I'll be jiggered! - You were all spot on - when I poked around with heavier poking sticks, a bit of fine powder showed up, so not a welch plug at all, it seems. I then used one of those right-angled drill attachments and a pointy drill bit to CAREFULLY eat into the silt - and silt it is. Very fine powder.
Now - Peter, Paul, Willy - how deep is it safe to carefully chew into the silt? I'd like if possible to get through it (not damage the gallery wall behind it), and then enlarge the hole as far as is possible so that coolant actually drains out. I'm only about 5mm into the silt so far.
Thanks all. John.


J P Hall

Also, while your thinking caps are on, can I expect the fluid in the thermostat housing to drop down if I create a hole through the silt in the drain plug? Bottom hose is still connected, heater takeoff plugged; top radiator hose open to atmosphere.
John.


J P Hall

I've just left mine blocked, it's not given me the slightest concern regarding cooling in over 30 years. True I'm not in Oz, but we do get it pretty hot sometimes - 30C plus.

You need to blank off both connections to the heater matrix to take it completely out of circuit. If the heater valve port in the head is already blanked off then you need to do similar with the return to the bottom hose. This could be as simple as shoving the pointed end of an old spark plug in the end of the hose that is taken off the matrix and clamping it with a Jubilee clip, to doing something more 'engineered' like replacing the teed bottom hose with a plain hose and removing the metal pipe over the rocker cover.

If you do bore through the silt then that will drain the remainder of the coolant, including what you see with the thermostat removed.
paulh4

Thanks Paul - so far we're ad idem - I've put rubber caps on the heater stubs, shortened a bolt to its shank to plug the bottom hose heater branch;
and removed (for tidiness) the pipe across the rocker cover.
I'm hoping Peter Burgess will offer an opinion as to how far inwards I can expect to find the coolant gallery inner wall; so far, using the arrow tip I reckon I'm 10mm in to the silt and I can feel what "could" be the inner wall, but still not a drop of coolant. I blew compressed air into the drain plug hole, and not a bubble to be seen at the t'stat housing. I'm thinking if I enlarge the hole next, with gradually bigger drill bits, the plug of silt might just give way if I'm lucky. Also interested in Peter's comment that IF the head was off, it's possible to drill vertically downwards and meet the horizontal portion, perhaps with greater success. But I'm not keen to separate the head if I can avoid it. In our warm summer temps, typically 30c daily, the car runs at just over "N" on the gauge.
John.
J P Hall

Hi John
Just measured a couple of 1800 blocks--One was 37mm deep the other 38mm deep until I hit solid metal--Both were about 1mm less at the front as the casting starts to curl around No.4 bore. so you can use as big a diameter drill that'll fit through the hole and go 35mm+ safely
I know you're on a bit of a learning curve so some info for you-
That drain bung is the lowest point for draining water/coolant out of the block---It goes into the main water/coolant chest that holds the coolant that surrounds the cylinder walls, it's all one cavity,same cavity that the welch plugs go into(see pic-same piece of string, no tricks), so yes if you drain from there it will drain everything out of the block from the thermostat down. After you get the crud out of the hole you need to get a pic or a bent piece of wire and poke around upwards towards the welch plug and all about to clean as much poo out as you can. "IF" you can't get a result and you're still thirsty you could knock that welch plug out and go downwards from there-

Now- Looking at your pic. your engine has cup style welch plugs so yeah ,something different, maybe a relacement service engine of some sort.---maybe

I've got a trick question for you, the pic. i put up with the string in the hole----You, young Grasshopper, have to tell me what this engine is out of.

And ---by the way-Thankyou, while I was checking the 1800 blocks i found a good crankshaft in one of them that i forgot I had--bonus,yay

Cheers
willy


William Revit

Seen that pic before :o)

My Gold-Seal engine has cup core plugs and Peter told me that was part of the Gold Seal rebuild although someone else with the same 48G733 prefix as mine sent me a photo of his with 'flat' plugs. The edges of my plugs are flush with the face of the block, but a picture of a third 48G733 has cup-type recessed, which potentially leaves room for a flat to be put on top of a cupped.
paulh4

John---bit of reading material for you-

https://www.theminiforum.co.uk/forums/topic/351196-unusual-engine-number/
William Revit

That's exactly what I needed, Sir Willy - thank you for going to the trouble. Armed with those numbers, I'll take it a bit further over the weekend. As Paul points out, I could technically "leave well alone", but I'm not built like that. I'll drill and poke and see what gives, but stopping short of pulling the head off. Too many other jobs to do!
I had stumbled upon those miniforum discussions ( I did up a nice '78 Clubman for son no. 3 in 2010); they also seem to be stumped on the DBL 230 engine numbers. I'll just have to live with it. As said, she runs sweet as a nut.
Now - the "piece of string" picture - I have no idea, but what's the go with the absent distributor? It must be some kind of steam-driven contraption, canal boat ... Be interested to know.
Thanks always.
John.
J P Hall

You will not clear the crap from the plug side of the block enough to let the water flow again, it has a small hole about 8-10 mm and maybe 30mm deep leading to the plug from above the plug. You may as well wait until you rebuild the whole engine
Peter Burgess Tuning

I should probably close this off by confirming that despite my best efforts and tremendous support from all who chipped in, I succeeded only in drilling a 10mm hole 25+ mm deep, retrieving a neat pile of very fine silt, and nary a single drop of liquid emerging from the drain hole. What an exercise - sore back, disappointment, ... but no regrets about trying. At least I now know from Peter, Paul and Willy (remember them??) that down the track it can be done, once the head is off.
Thank you all. I shall now order up a replacement heater valve, thermostat etc. and enjoy using the B again.
John.
J P Hall

If you're going to drive the MGB then that TC will be excess to your requirements -- i can get a mate to pick it up just give me a couple of days notice to get it sorted.
lol
willy
William Revit

Ha! Not bad humour for a Taswegian.
So come on Willy, what's the answer to the "string in the block" question . I couldn't sleep last night. John.
J P Hall

Ha ha--ripper, no sleep
You probably noticed the block has no hole for a distributor-----
Twin cam MGA--The distributor runs out of the timing chest up front.
sleep well

William Revit

Nice one, Willy.

I initially thought it might be a diesel, but that still has a hole down there for the injection pump.
Dave O'Neill 2

Ooh yeah, lovely piece of kit that twin cam. No more room in the shed ... Unless I offload the motorhome of course. John.
J P Hall

This thread was discussed between 04/01/2024 and 07/01/2024

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