IMPORTANT !: I never etched the hairpin, because of the "suddenly" revealed circumstances.
In the post, I decided to share my experience: why, taking up this business, you can fail and how to make your life easier if the stars are supportive of you.
Since the time is late, and today I fucked terribly with this stud, I will try to be short and to the point.
Background: I have a Suzuki SV650. Not on the move - there is no chain, many nodes are in varying degrees of disassembly. The motorcycle has an L-shaped twin-cylinder engine (V-shaped with a camber of the cylinders 90 degrees).
Due to the fact that I have an awl in a soft place and I can't sit quietly, I decided to unscrew the bolts of the exhaust pipe in order to remove it. Why I will not describe not about this post. Three bolts with mats came out, and one went sour… LETTING FOR LOT. Than I just didn’t water it as soon as I didn’t persuade, but with the next jerk it broke off. A small piece remained to stick out.
First: if you have such a problem, do not rush to drill.
If space allows, try to weld a nut and turn it out for it, it helps many, I have not tried it, since I have no welding machine, no friends, no one in the neighborhood knows how to cook, and yes, even in garages, some people like to stand up to look at the car with a serious view.
Second: if for you a welding machine, this is an egg boiling machine, then try to take a thin drill, very thin and drill 2-3 holes in a row in the hairpin next to them so that you can drive a slotted screwdriver into them (or better a head with such a screwdriver) and try to unscrew it all the same. I learned this method too late, when there was already one big hole in my hairpin, but it could have all ended so quickly and simply.
Further, you can continue the list of methods such as extractors and similar devilry, but I will not, since all this is only suitable for just a broken bolt in pure metal or wood.
And I have a M8 bolt stuck in the front cylinder - in a terribly inconvenient place.
This is where the juice itself begins, as they say.
Attention! The hero of the story. The one below.
He's full face. 
At first, fishing rods were thrown here, on the forum in the sense. I received a lot of advice from the guys, but they all almost boiled down to removing the head and transporting it to the nearest turner or repair plant or lathe plant ... I still did not understand where to look for them and most importantly how to get the local turner to help me with something, He's not standing in front of the gate with a sign I will squander dviglo. Since for me, in general, removing the head is too much ... since I am not corny a mechanic, I don’t know the internals, there is nothing to jack the engine and there are many more reasons “against”, I decided to use the last available anemic method - etching the bolt with acid, nitric HNO3 if my memory is not changes.
We climb into the vastness of the Internet where we read that nitric acid dissolves most metals with the exception of gold, stainless steel, platinum group metals, a couple more metals that are rarely found in the hands of the average person and, most importantly, aluminum from the alloy of which the engine is made.
That is, if you pour an iron bolt into aluminum can nitric acid, then the bolt will gobble up, and the can will remain intact.
For all this orgy, I needed:
Nitric acid. I live in Moscow, where everything that you can buy is concentrated, and what you can't just need to look a little longer. Here I found it in a chemical store. If you are not from Moscow or St. Petersburg, you need to look for it either in the same stores or at chemical factories.
Since this reagent is very harmful, I needed gloves rubber thick thick, mask which has been replaced by a painting respirator (better than nothing) and protective glasses, they are necessary, but the acid did not get on them, but a couple of times when manipulating the reagents there were splashes.
Plastelin, he did not care about acid, he sculpted a funnel from it over a hairpin. Soda- an aqueous solution of soda serves as an acid neutralizer, but their reaction is very violent, from which there were splashes described above. A couple of syringes. A couple of containers (bottle cans). The water is ordinary. Aluminum foil - to protect the surrounding areas and parts of the motorcycle.
So everything is there. A few words about the already mentioned acid. The main thing to remember is safety. A broken bolt is nonsense compared to chemical burns on the skin and mucous membranes. Acid, even diluted, is toxic, even without reacting, it soars - it releases corrosive volatile substances. When interacting with dissolved metals, the reaction is very violent with the release of heat. During the neutralization reaction with soda, nitrogen oxide 2 is released, which is very toxic + intense bubbling occurs and if such a reaction occurs in the bottle, a "fountain" is possible. Do not work indoors.
Let's continue on the frivolous. With the effort of the fingers, this miracle was done. 
Funnel for acid. At the end of it is a hairpin reamed with a drill 6.
After reading the information on the Internet, I found out that an acid in the initial concentration of ~ 67% sold in stores can enter into an act of love with aluminum, but diluted to 30% (as well as pure 90%) passivates aluminum, that is, does not react.
We dilute the water with acid. That's right, and not vice versa - pour acid into water as taught in chemistry lessons. If on the contrary, it may splash.
They mixed it, spit it out a little, took it into a syringe and poured it into an improvised plasticine bath.
And they went off to drink tea with milk for a while.
Come - WAH! The thread is as clean as… clean in general. There are no hairpins, you can add cognac to your tea, although it’s probably rubbish with milk.
…
I also thought it would be so.
He came, looked, and there, as it was quiet and smooth, it remained, the aluminum of the engine is intact, the hairpin is also nothing like that.
Maybe I think the acid is weak, it turned out very well, they say, it was overdiluted. I went and took the first bolt I came across from the box and threw it into a bottle of diluted acid from which I was just typing it into a syringe. After twenty minutes, the bolt disappeared, leaving a slight cloudiness behind. And there is quiet ...
You probably, like me, did not read this sentence very carefully, just above: with the exception of gold, STAINLESS STEEL, platinum group metals, a couple of metals that are rarely found in the hands of the average person, and most importantly aluminum.
Eg the hairpin bitch turned out to be made of stainless steel, a kind former American owner. In general, I poured everything with a solution of soda - plasticine and the rest of 30% acid in the bottle for which I received a fountain of reactions and wandered home sadly.
Bottom line: Check what you broke off. Indeed, a 30% solution of nitric acid dissolves the metal as if it were not aluminum and stainless steel. You will not have time to blink and there is no hairpin. And if your usual cheap bolt in aluminum or stainless steel breaks off, then this way very effective and cheap, and most importantly not very labor intensive. The budget is about 1000 maximum including everything (protection, acid, accessories). The time is 1-1.5 hours.
That's all. Good luck to all. Take care of yourself.
Broken studs are one of the common defects that a motorist may encounter. Studs are used in many parts of the car. But if you do not have a car, this does not mean that you will never get into this situation, because the bolt can also break.
The way to retrieve the debris that I will show, it seems to me, is one of the simplest and most effective. It will work even when the debris is 2-4 mm deep inside.
We extract the fragment of the hairpin
So let's get started. To begin with, we will measure the diameter of the hairpin by its fragment remaining outside. In my case, it is 8 mm in diameter.
We take a wooden block and glue 3 layers of masking tape on top of it. Then we make a hole in all three layers with a diameter smaller by one millimeter.
Cut out an arbitrary path. And we got such a gasket.
We glue it on the hole with a fragment of the hairpin. This gasket will protect the threads when welding.
Further, you need to take any L-shaped steel corner with a thickness of 2-5 mm. And drill a hole 7 mm in diameter in it.
On the reverse side, make a hole for the taper with a large drill.
We put the corner on the hole and fix it with pieces of masking tape so that it does not fall during welding.
The holes must match exactly.
Welding time. It is advisable to use a semi-automatic welding machine. Well, if not, take a regular one with a thin electrode.
First, we fuse a layer onto the chip.
This is how it looks after the first time. Let's wait a bit.
We weld on another layer for reliability.
Well, now, you can try to unscrew the hairpin.
Everything turned out fine. Welding warmed up the chip and it became easier to unscrew.
This is how it looks up close.
We put a new hairpin
As you can see, neither the thread nor the area around, nothing was damaged after welding. We sand the site with sandpaper.The tale of how I won the exhaust manifold.
99% of Saturn Vue owners with a 2.2 liter engine experience exhaust manifold cracking. Usually everything happens like this: first, the rightmost hairpin breaks, then the next one after it, and then the collector itself bursts in the middle. This is usually accompanied by a fart sound and jerking of the car. There is an opinion that it all starts with a clogged catalyst.
I didn't notice the crack right away. I didn't have much sound, but the smell of exhaust went into the salon when the engine was parked with the engine running. Also, there were failures when starting from a place.
On closer inspection, I saw a crack in the exhaust manifold. And also torn hairpins.
Then it was decided to brew on their own. I read literature. I drilled holes, cut a seam with a grinder, took electrodes on cast iron, cooked for half a day, when it cooled down, the seam vomited. I could not weld it myself, I thought to seal it up with a patch and an asbestos cord, cut the seam with a grinder again, put in asbestos, cut a thread, put a patch, it turned out even worse than it was (farting sound, smoke, and big jerking of the engine.
It was decided to bring it to the specialists, I looked for such a long time, read the reviews, found it, brewed it in 15 minutes, without any drills and ovens, their apparatus is the size of a small refrigerator.
The plane led. The middle bent 2 mm away from the motor. It was necessary to mill.
Having spent 3 days of time and knocking down the rapids, I did not find specialists in our city. Some are impotent. Give everyone a straight and small collector, they say we can't clamp your ...
It was decided to cut it myself.
I bought sandpaper 300 and 800 large sheets, pasted it on the countertop, fastened the top of the collector to the drawers with an elastic band so that it evenly stood up without distortions to the emery, and drove it with water to grind with 8 figurative movements.
I didn't bring it out ideally, of course, half a millimeter or less remained, I was tired, I decided to do it.
The thermal gap between the two middle legs on the platforms disappeared after welding. I cut it through with a grinder again.
Now you need to make studs, otherwise it will break again. Bought a new pad, plasticine, large syringe, soda and nitric acid HCh (it contains the largest% of acid). See in the photo. I made grooves from pieces of a bottle and plasticine, diluted the acid with water 1 to 1 and poured this mixture into the grooves (without dilution with water, the steel is oxidized and covered with a film, as a result of which it stops etching). I changed the mixture about once every 3 o'clock except at night. Taking into account the temperature outside about 12-15 degrees, I poisoned 2 hairpins at the same time for 4 days.
Take care of your hands, I burned mine by negligence a little. Also, do all the procedures on the street because acid vapors are very harmful.
After etching, we treat everything with a soda solution to neutralize the acid. Studs fit from many cars, including Russian ones. To install the collector, I used wide washers and brass nuts instead of native steel nuts, smeared all the threads in front of this with copper grease.
I tightened it up like a spiral. Starting from the outer studs towards the center. That is, 4 cylinders then 1 then 3 then 2, in several passes. Do not rip off the brass nuts, they are softer than steel nuts.
Good luck to all!