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MG MGB Technical - HELP Broken nut from hell

As you may know I have the head off my B to try and sort out my compression problems.

I started putting it all back together last night, I had brought new nuts and bolts where needed from Moss. As I tightened the bolts into the heater valve one broke. Turns out the bolts they had sent were too long and I had not checked.

Anyway, I started to drill it out and the bit broke off, started with another bit and that broke too. Managed to get to a good depth with a 3rd drill and tried to use a screw extractor...That broke off too.

So, now I am stuck with a broken nut with two hardened drill bits and a hardened screw exractor stuck in it. I am trying to keep drilling but the drills are getting nowhere.

Can anyone offer any advice, please.

Graham
G Lewis

Hi Graham.

A fairly common problem, but a tricky one.

I assume that there is not any bolt shaft to get 'hold of' or weld a nut to ?.

Take a look here :

http://www.pirate4x4.com/forum/showthread.php?t=79728

Don

Don

Carbide drill bit is what you will need to drill out the hardened bits. The machinist where I worked used cement drill bits to do just this. I do not know if they re-shaped the tips, but the bits were much cheaper than purpose built ones.

Pete
Pete

Hi,

1) Without seeing the condition it is difficult for me to comment specifically.

2) However, based on your description, things do not look good.

3) As suggested a carbide drill will defintely cut the drill rod (usually a D2 type material) that is now in the way, but the problem will be to find a center. Any drill now used (carbide or regular) will want to walk to the side of the existing drills in the hole, and probably start drilling out cast iron threads.

4) I suppose the screw is a 1/4-28 which due to its small diameter makes things more difficult.

5) Poor quality screw extractors will ofter twist and break off, making things worse. They often make things worse by expanding the screw outward and actually causing the screw to seize more, not less. The worst extractors for doing this is the long spiral type with wavy non-sharp bitting edges, and the best for not doing this are the kind that bit on the corners, or the short less tappered ones with sharp not too deep of flutes.

6) If too large of a hole is drilled, then expansion is more severe, and if to small a hole is drilled then extractor breakage is more likely.

7) Anyway on with the problem. If using a carbide drill is attempted, do not use some cement carbide drill bought at a hardware store. You would need to purchase one from an industrial supply house. And being extremely hard and brittle they will break way easier that the standard "jobber drill" now broken off in the hole.

8) Now for a story related to this problem: In 1960 I was fresh our of high school, and working in mechanics while getting an advanced education.

9) My boss had a Jeep he used for plowing snow and pushing cars. He twisted off a screw (either 5/16 or 3/8 inch diameter) down on the side of the 4 cylinder block.

10) He told me to take the Jeep to a welder who had a weld shop, and who use to attach plows and trailer hitches to vehicles for us, and see if he could get the screw out. At the time this man was probably 55-60 years old, and obviously had been around the block a few times.

11) He got his oxy/acetylene cutting torch lit up with an intense probably 1.0 inch blue flame, stuck the tip of the flame at the head of the screw, and when he applied the oxygen I saw something that I had never witness before, even though my dad was a welder/mechanic by trade, and I had seem him do some impressionable things.

12) I remember standing their thinking, "What is he doing, he is going to melt the block and threads"? Anyway, molten steel started flying out of the hole, and in less that 10 seconds he stopped, went and got a screw, threaded it into the hole, and said there you are. I got in the Jeep and left---he build us for the work.

13) A few years later while working in industry with exotic alloys, I thought back on what I saw and was able to better understand what had happened.

14) Both the cast iron, and the alloy steel screw, would melt a approximately 2700-2800 degrees F, but the screw would oxidize more readily that the cast iron, and further the cast iron with the water jacket near by would be acting as a large heat sink. So with the right skill set (low dwell time, correct flame and applied oxygen, he was able to literally turn that steel screw to molten slag and blow it right our of the hole with out any noticable damage to the threads in the cast iron. The cast iron change color a bit, but that was all. And being that cast iron is not a heat treated alloy, any annealing that may have taken place was a non-issue. The block has already been through a zillion thermal cycles and undergone some annealing and stress relieving, since it casting at the factory. He did not even have to chase the threads with a tap. It sure impressed me, a just-starting-out 20 year old.

15) Now, if you had access to an oxy/acetylene torch
you could apply some very focused heat onto the screw and broken drills and possibly soften them enough to permit easy drilling.

16) I am not talking about using a cutting torch here, but simply a very hot focused blue flame. But it some skilled person was at the wheel, you may be able to do what the welder above mentioned, did.

17) At approximately 800-1000 degrees F, the D2 drill rod should soften quite quickly, and the cast iron, even red hot at 1200-2000 degrees F will not be detrimentally affected. The only concern would be local stress build up in the heated zone and a possible fracturing of some already stressed cast iron, but I see this as low risk.

18) Short of heat, or sloppin' out the hole, and retapping off center to probably a 5/16, etc, I do not see much else you can do. If heat is used, do not attempt to use a propane/butane torch. The heat must be focused, hot and in high quantity, with a person on the other end of the torch that somewhat understands heat and heat transfer in metals.

Layne

Layne Wilson

What a pig, this sort of thing really tests you when you are on your own in a cold garage. I think you need to get the car to an engineering works where they have the kit to do this, maybe by using a diamond tip drill and tapping it out oversize, maybe a cork or rubber bung could keep the water in the block long enough to get you there?
Stan Best

Thanks for the replies.

Well, I had a go with a short thick type extractor and did nothing other than rip the top part of the bolt out. It looks like game over really.

What are my options now?

1) Take it to a workshop (the head is off)

2) New cylinder head. Might be ideal time to get an unleaded one.

3) buy some very hard drill bits and try again.

The hole will need rethreading now as the thread (at least at the top) is probably gone as my initial hole was very slightly off centre.

If money was not an issue then I would get a new head on Monday, however things are really tight right now. Wouldn't be so bad if this was not my daily driver now. I'll have one last bash with the drills tomorrow and then I'll start saving. If anyone has a spare head they want to sell for a fair price to fit my 77 then please contact me. Also, if anyone can suggest a good workshop which might be able to help for a fair price then let me know.

I have had a few bolt nightmares in my time, but never anything like this.

Thanks again

Graham
G Lewis

Graham. You might contact Peter Burgess or Chris Betson by e-mail and see if they can provide a good used head. Just spent three days working on my daily driver, overdrive transmission began acting up, and had to pull the engine and tranny and install a stock four speed into the car. The trip to work was its road test. Still some problems to be sorted, but, it got me there and back. So, I know what you are going through.

Les
Les Bengtson

Since the head is off I would take the head into a machinist and having a heli coil installed. They have all the right tools for problems like this

FWIW


Bruce
Bruce Mills

The hole is definitely going to have to be heli coiled (or Re-coiled), but first, all the bits and pieces have to be removed. Start checking around for a shop that has a EDM set up and take the head to them to get all the bits and pieces out of the hole. I forget exactly what the initials stand for, but basically it is the same process that Layne discribed, only using an electrical arc to do the removal only it doesn't take someone with a lot oa experience to accomplish it as it would with a gas welder. Good luck - Dave
David DuBois

EDM stands for electrical discharge machining. It is a non-traditional method of machining that uses sparks to remove metal.
Steve Buchina

What Dave refers to is Electostatic Discharge Machining, where a carbon (usually, but other materials are sometimes used) electrode is slowly fed down into the hole while a dielectric fluid similar to kerosene is flushed over the part. A fairly high current charge is passed through the electrode, and the spark actually eats away the metal, while the liquid flushes away the slag generated. Hardness of the metals involved is no obstacle to the process.

This is often used to remove broken taps from aluminum castings, so it will be more common in areas that have metal manufacturing facilities that might produce complicated castings where throwing away a half-finished part is not financially feasible. I believe the charge runs about $20 per hole, from what I have read, but it obviously varies by area and availability.

Best of luck - - Alec

Alec Darnall

Very interesting and clever application of chemisty and physics Layne,
I had the same problem (same bolt) about 15 years ago and I've always wondered how they (I patheticaly took it to a mechanic) got it out.
Peter

No shame in getting help, I'm sure we all have specialities where pro mechanics would be grateful for our help. I find small engineering firms are usauly happy to help with an MG and not very expensive, most wish they could still help Abingdon with a 500 pieces per week rolling purchase order!
Let me know if you are stuck, my neighbour with the re-shelled B works at a privatley owned engineering company here in High Wycombe.
Stan Best


An alternative approach if there is enough metal in the head could be to run a pipe thread into the water channel itself. Then fabricate a steel base plate for the heater
valve and after a trial fit, have it welded to the appropriate BSP fitting. It would not need to project very far out from the head when screwed in place.
Vic
V Todman

Steve and Alec - Thanks for filling in the missing words. I knew it was Electrostatic Discharge _ but could remember the M word :) Cheers - Dave
David DuBois

Ordered a new head today with the plan of fixing and selling the old one to get some of the money back.

Drilling out the broken bits is working with titanium tipped bits, but its slow going...2 hours to go 1mm!

I need to get the car back on the road now. SHould get the head and fit it on Wednesday, MOT Thursday and hope there is not too much additional work required.

Thanks for all the help

Graham
G Lewis

This thread was discussed between 23/09/2006 and 25/09/2006

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