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MG Midget and Sprite Technical - Removing an allen headed plug

You will note from another thread that I'm about to replace my cylinder head. As part of my thinking I thought I would upgrade to an 11 stud fixing rather than the standard 9 at present. When Peter May built my engine he kindly drilled and tapped the block ready for the two extra stud/bolt and plugged the holes with an allen headed threaded plug. So making the change should be easy. Of course it's not that simple. The plugs have been in over 4 years and will not shift and the allen socket has become round as the result of my efforts to shift it.

I'm looking for advice on how to extract these plugs. Easyouts are generally considered a risk (breakage etc.). I don't see how I can apply heat as they are at least 3/4 inch below the deck of the block. Some suggestions involve bashing a torx head into the hole but I'm thinking that it might be OK to drill them out as any swarf would go into the waterways (not the oil ways). If I follow that route - any tips (e.g. don't!)?

Alternately, any other suggestions. The default position is leave well alone and stick with 9 studs.
Chris Hasluck

I would drill them out if going the 11 stud route. When I had the my block done for 11 studs IIRC the machinist fitted the front smaller, 5/16" UNC ? for a bolt, tapping with a stainless thread insert as it goes into the water jacket, I don't think the rear one does and uses a normal head stud.
David Billington

I'd leave well alone and fit the 9 stud but if you're going for it I would do the following...

1, bash a torx in it but don't snap it or you really are f**ked
2, drill it with ever increasing drills until you reach a tap drill size. Tap to the correct size.

Don't drill all the way through and you will be able to collect the swarf at the top. Once out to tap size drill the last bit of steel out of the bottom. One of the issues you'll have is keeping the drill centred and square. The use of a suitable sleeve in the top 3/4 inch will help as would a using mag drill (drill with a magnetic base).

Best of....
MGmike
M McAndrew

If you have managed to round them off they must be of fairly soft steel.

If you are saying they are 3/4" down and you are resorting to drilling them you could look at using 'centre drils' and get one that is as big as will go down the hole - as they have smooth sides and will help to get the drill somewhere roughly in the centre.

Then using the 3/4" of thread you already have use first/second taper taps to clear out the remainder.

Bit of a bitch job really and a degree of luck required.

R.
richard boobier

On my block I don't see how the front tapping could be 3/4" down as the block isn't that thick there, that would be difficult for the rear also I feel. Do you have a picture.
David Billington

Following up MGmike's comment about leaving well alone, is there really any great advantage in 11 studs (OK there must be some but is it really worth the effort?). I have to admit to a considerable amount of conservatism in matters like this.
Chris Hasluck

I'd leave well alone. The last thing you want to do is scrap a good block or at least go to the expense of having it repaired.

I run mine with 9 studs and they aren't even ARP, just the std dimpled ones. It does occasionally blow gaskets but only once at the front where the extra stud might have made a difference. When I say occasionally it's only been twice I think in the last 10 years of hillclimbs.
john payne

Coincidence?

I've got a broken tap stuck in the front 11th stud hole in my block. It's broken off below the face of the block.

How the f do I get THAT out?

Does it matter?

Nope. Having broken that tap over 15 years ago, I didn't bother to try. When I pulled the head a few weeks ago, the gasket was as sound as a pound in that area.

The front extra stud is actually a bolt. 25lbft torque. The rear extra stud is the same as all the others, with the same thread and same torque applied to it.

Still, I'd like to know how to remove the broken tap.
Lawrence Slater

Thanks guys - I think I'm going to leave well alone.
Chris Hasluck

Lawrence,
The way to have your tap removed is by spark erosion, that's the way it done these days, yours is a fairly common scenario, See Wikipedia ; Tool removal by metal disintegration machining.

Not cheap, but think of all that money you have saved on front wheel bearings over the years!

Ian
Ian Webb '73 GAN5

Id leave it alone, I had mine converted to 11 stud, im not sure there is much advantage as the front stud is only torqued to around 15 ftlbs... not the 50 lime the other 10 studs

As to drilling the block...

I found a great way about a year ago, get a strong round magnet with a hole in the center the same size or bit bigger then the drill, place a piece of butcher paper over the hole in the block stick the magnet on the block over the butcher paper and line up the holes... then drill it, the neat thing is the drill becomes magnetized as your drilling (slowly with cutting oil) and the swarf collects to the drill and the remainder to the magnet...the butcher paper keeps the block from scratching

In the end, no metal shavings inside the engine

Prop
Prop and the Blackhole Midget

Id leave it alone, I had mine converted to 11 stud, im not sure there is much advantage as the front stud is only torqued to around 15 ftlbs... not the 50 lime the other 10 studs

As to drilling the block... I found a great way about a year ago, get a strong round magnet with a hole in the center the same size or bit bigger then the drill, place a piece of butcher paper over the hole in the block stick the magnet on the block over the butcher paper and line up the holes... then drill it, the neat thing is the drill becomes magnetized as your drilling (slowly with cutting oil) and the swarf collects to the drill and the remainder to the magnet...the butcher paper keeps the block from scratching

In the end, no metal shavings inside the engine

Prop
Prop and the Blackhole Midget

Like this then Ian.

http://www.youtube.com/watch?v=YbeKxFBZrF8

Cool.

25lbft Prop. Surely.
Lawrence Slater

I've used 25lb on the rearmost stud, as well.

I figured that there was originally no clamping there, so 25 would be 25lbs more than standard.
Dave O'Neill 2

I thought it was a bit odd too Dave. I've got the torque spec for the Austin 1300GT -- which is the head I've got --, and the head torque settings in the book gives the usual lbft for the 10 studs, and 25lbft for the odd sized special shaped bolt at the front.

But since I broke the tap, I obviously haven't had a bolt at the front. Just the rear extra stud, which I did to 50lbft or whatever the books says.
Lawrence Slater

Hmmm .

I could be wrong on the front stud torque, but it is a weak spot as to much torque will bust the block...I certianly wouldnt torpue past 25ftlbs but at 15ftlbs, im certianly safe, head gaskets are way cheaper then engine blocks here in the usa

But the rear 11th stud is safe to torque to 50ftlbs... thats an area of solid plate of steel armor

Prop
Prop and the Blackhole Midget

" it is a weak spot as to much torque will bust the block."

That's why it's only 25 Prop. But given that most people with hot heads don't even bother with more than 9 studs, perhaps it was always a waste of time anyway. I guess BMC thought at the time, that it was needed.

How many studs on an MG Metro turbo?
Lawrence Slater

I guess BMC thought at the time, that it was needed.

Ive wondered about that... my guess is possiable head gasket locating, plus marketing

Its odd that there is no locating pin on the block or the head to centralize the headgasket

Otherwise why bother adding an 11th stud with so little ftlbs of clamping torque

Prop
Prop and the Blackhole Midget

"How many studs on an MG Metro turbo? "

9

"Its odd that there is no locating pin on the block or the head to centralize the headgasket"

Prop, it has been stated before - when you were busy wrapping tape, or some such, around your studs - two of the stud holes in the gasket have less clearance, which locates the gasket on the studs accurately.


Dave O'Neill 2

Lawrence,

Do you remember if the tap is HSS or carbon steel. There are some simple DIY spark eroder details on the internet so you might be able to make a crude one to do the job in situ otherwise a pro job is likely to need an engine out and strip. There are other ways to remove broken taps but without seeing the patient I wouldn't want to comment and being in cast iron and not that thick doesn't help, not to mention 15 years.
David Billington

Block is naked on my bench David. I've no idea of the hardness, other than it was a clean brittle break, and didn't twist and tear.

It'd be nice to get it out just for the hell of it, and I may have a chip away at it for a 1/2 hour. But I'm not really that fussed, esp if it's an arm and leg to get it done by a pro shop. :).
Lawrence Slater

Lawrence,

Both HSS and carbon steel will have a clean brittle break, or should do for a cutting tool unless cheap crap, it's just that you stand a chance of annealing carbon steel in situ to a state where it can be drilled, HSS not so.

Can you post a picture.

I would start by gently tapping any accessible flutes to see if it can be moved, if so good. Sometimes you can get small rods, like drill shanks, down the flutes to try and get a grip and turn it out, there are commercial items of this type.

I mentioned earlier that IIRC this front extra bolt goes through into the water jacket so the machinist I used put a stainless thread insert in as standard and if that is the same in your case then a bit of axial tapping may aid loosening the tap bit then get a thread insert fitted to correct any damage to the CI.
David Billington

I drilled the block myself. In fact I've drilled two of them. Both in the road outside my house. I bolted the head on and used it as a guide, and then tapped the holes. Neither of them hit the water jacket.

The 1st block was a success. The second one is the one I broke the tap in. I think I was a bit impatient and was going too fast.

Yup. I'll post a pic tomorrow.
Lawrence Slater

Well in my experience tapping CI is a piece of cake but maybe in your rush you bottomed it out and broke it. I can say that tapping with a blunt tap is one of the most stressful things I can think of, I mainly have metric taps and some common UNF, UNC, and BSP, but my neighbour has an extensive range of BA, BSF, BSW, ME, and some UNF and UNC, many of which he acquired and are worn but I borrow if I have the odd job requiring such a thread and it is hellish stressful tapping a hole with an old blunt tap knowing what the outcome of removal may be, not broke one of his yet just my own.
David Billington

Hi David,

Well I did 3 holes ok, 2 in one engine and 1 in this one.

But yes you're right. I did bottom out. I've just passed a bit of MIG wire down the open flute you can see. I can feel the smooth side of the tap all the way to the bottom, about 17mm.

You might think I could turn it out. But I've tried with needle nose pliers and some circlip pliers. It just bends them. I've also tried -- again just now -- tapping it round with a punch. It's like hitting solid metal. No give at all.

PS. I've jusr had the block very lightly skimmed, in case you may wonder.

Lawrence Slater

This is a stupid idea,

But what about filling with gasoline having a small punch and hammer close by then light it up for a moment then immediately try punching it from the side angle to loosen it up...

The flame would be hot and fast with out warping the top of the block and cause some expansion...heck maybe try freezing it 1st before setting on fire

Like I said, bad idea but its so crazy it might just work

Probably just needs a nudge to break free of the fine threads

Prop
Prop and the Blackhole Midget

Not now I know it's bottomed out Prop. That means the threads of both the block and tap are well and truly stuck on eachother.

It'd be nice to get it out, just for the satisfaction of getting it out. But nah. It can just stay there now I guess. Esp' as this is going to become my spare engine, with a 9 stud head on it. So it won't really matter anyway.
Lawrence Slater

Id love to see the future owner in 10 years from now open the engine up, and see that

Thats going to be a real ""WTF"" moment

Reminds me of me 25 years ago, id open up dryway and write all kinds of crap inside like how cool hitler was, and how evil jesus was so worship satan, and on and on...that way in 50, 100 years from now the next person to open the wall up would get freaked out...

a real gift to the future on my behalf...haha

Prop
Prop and the Blackhole Midget

Lawrence, this is something that you probably won't want to try since your stuck tap isn't causing a problem.

I have tried it twice and it worked once, with a sheared, bottomed-out stud in a prewar diesel engine. I couldn't drill it as it was sheared at a bad angle and I couldn't get a centre.

I used a 4sq/mm (IIRC) stick welding electrode and turned the current as high as it would go on my welder. Carefully centred up and banged the tip of the stick on the stud. (Physical contact so no arc so no spatter). I just held it there until the thermal cutout on the welder shut off the current, then released the stick from the holder, took off the earth and put the welder away.
After about 5-10 minutes I was able to unscrew the stud using the stub of the welding electrode and some spray lube.

The thread in the block was a bit of a mess and I ended up Helicoiling it.

Desperate measures I guess but it might help someone in the future. Might even help Chris if he's brave enough!

BTW I've been waiting 25 years for that old welder to die so I can treat myself to a nice modern one. Can't kill the bloody thing!
RS Hughes

Easy_Spark_Eroder.pdf http://www.usinages.com/ressources/file/199881

I think you could make a much cruder spindle assembly as after all you're just looking to remove a broken tap.
David Billington

GREAT post David!
Might have a go at making one for fun.
RS Hughes

I'm warming (no pun intended) to Prop's idea. Throw petrol on it and light a match! That's certainly how I feel at present.

Chris
Chris Hasluck

David, that reminds me of the welding kits you used to get in the 1970's that operated from a 12 volt car battery. That had an electrode that vibrated breaking the current in the process. I think it worked on inductance though rather than capacitance as in example in the .pdf file.

Rob
Rob aka MG Moneypit

Rob,

I think I know what you're referring too having seen the adverts but never seen one in the flesh or used one. That PDF has a power supply using capacitors but the electrode is pulled away from the work by an electromagnet (inductor) to break the arc powered by the current flow doing the eroding, I think the idea is similar to the welder in some respects.
David Billington

The 'Kel-arc' welder worked from a car battery, or two in series.


It was also supposed to help with welding thin panels, when used in conjunction with an arc welder.

I did buy one, but I can't remember whether I managed to weld anything with it.

It's probably lurking in my mother's garage, somewhere.

I must have a look for it, the next time I'm there.

Here's a pic I found on t'net

Dave O'Neill 2

Hey, that's the one. I welded a set of outer cills to my Mini van with one of those in 1972. The only problem was the flexible contact, basically a multi strip brass contact. Sometimes an errant blob of molten steel would land on it and blow part of it away. Given enough time it would sever completely and stop welding.

Rob
Rob aka MG Moneypit

Lawrence
Not saying this will work for you but--
If the tap is bottomed out as we think it is, it might just be that a good wack on the top of it with something like a 1/4" pin punch or the biggest one that will fit the hole, might be enough to put a little dent in the bottom of the hole and be enough to free the tap. Then give it a good squirt of freeze-it and it might just be loose enough so that you can get it out with the pointy nose pliers or tapping it round
I've had a lot of luck with freezy pressure packs,they work magic
Tried it on a warm beer glass, very special result,blew it to pieces, almost as speky as them gold rimmed cups in the microwave-
willy
William Revit

Freeze it... R-12 air condition refrigerant ?

Would R-134a refrigerant spray as cold as the old R-12

Prop
Prop and the Blackhole Midget

If this was a less valuable block, I'd have a go with some of these suggestions. I might even try and MIG a rod onto the top of the broken tap. But as it is, I've got a perfectly functioning 1275 block. The only thing I've got to gain by getting the tap out, is some kind of satisfaction. I've got a lot more to lose if it goes wrong, and I damage the block.

Hey Chris. In your first post you said :
"-- tapped the block ready for the two extra stud/bolt and plugged the holes with an allen headed threaded plug. "

It occurs to me, that I should do the same thing. Up until now, I've had the broken tap blocking the front bolt hole, -- almost completely -- , and the rearmost 11th stud hole, was filled with a stud. On the front, because I had an 11 stud head on the engine, the top of the broken stud was open to the air.

Now though, I'm going to put a 9 stud head back on. That means, the rear hole in particular will be completely open under the head.

Does this matter? Does it matter that there will be an empty chamber? Could the air in there expand with heat, enough to cause the HG to fail at that point? Is that why Peter May put in blanking allen studs?
Lawrence Slater

Lawrence I think the plug is to protect the threads. If open to air, however little, the constant heat cycles will cause corrosion / rust and in time destroy the threads.
David Smith

Ah right. Cheers David. I'll get a suitable plug for the rear hole then. But I doubt anyone is ever likely to need it.
Lawrence Slater

Prop
Just for you----- get some it's magic

Crc 5002 Freeze Off Super Penetrant - Walmart.com


Do you still have R12 over there
It's been banned here for years

willy
William Revit

Yes... I didnt know if anyone would catch it

About 35 years ago in high school, I worked part time at sears as a tolit gruber, we used R-12 to remove chewing gum from the store carpeting and various other messes

I look that up, thanks willey

Prop
Prop and the Blackhole Midget

Arctic spray over here.

But this is even cheaper.
Unigloves Polar cold spray

http://www.praxisdienst.com/en/Topics/By+field/Dentistry/Unigloves+Polar+cold+spray+neutral.html?cur=3&speed=1&gclid=CPqXrZDtt8QCFSOWtAod23IAkw

And this.
http://www.screwfix.com/p/arctic-crack-it-shock-release-spray-400ml/83415?kpid=83415&cm_mmc=Google-_-Product%20Listing%20Ads-_-Sales%20Tracking-_-sales%20tracking%20url&kpid=83415&cm_mmc=Google-_-Shopping%20-%20Plumbing-_-Shopping%20-%20Plumbing&gclid=CPr88_ztt8QCFSQXwwodSiEAMg

Maybe I'll give that a go.

Lawrence Slater

This thread was discussed between 17/03/2015 and 20/03/2015

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