Best drill bit to remove broke cobalt bit?

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Does anyone have any ideas how much torque if can apply without the risk of breakage? Also, any additional tips from you guys that have had to do this before?
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How much of the bolt have you drilled out. Keep in mind the thinner you can get it, the easier it will move. If you can get it a bit thinner then it will weaken the strength of it.

If there is still some thickness to it, maybe drill it out some more in very small increments, and not enough to get into the threads.
 
Again, thanks for the replies. As far as "heat" goes, should I heat the bolt, or the head, or both? I seem to recall that it would be best to heat the area around the bolt without allowing the bolt itself to get as hot(?) then squelch with PB Blaster?
 
Word of advice : Heat without the Extractor in place, then drive the extractor in quickly and attempt to turn the broken bolt out.

If you leave the extractor in while heating, as soon as you try to remove the bolt, the extractor will actually "straighten out" the curved teeth that grab the bolt. I've got a few of em laying on top of the toolbox that I made that mistake on.

Also, I agree it looks like the bolt is drilled off-center, and the extractor may already be grabbing threads/part of the head.

In a worst case scenario, you may end up drilling out the bolt hole, tapping it and fitting it with a Time-Sert http://www.timesert.com/
 
Cant tell if its of center or not with the extractor in it. Like other have said, If the extractor digs into cast iron, it aint going to work.
 
I agree it looks like you drilled off center. Where you are at now I would blow the rest out with an oxy acet torch and clean the threads with a tap. Being it is drilled through work fast with the torch and you will be shocked how nice it blows out.
 
Snap-on has a nice kit with "bushings" that you can use to center the drill when you drill it out, but it's too late for you to do that now.

Yes, remove the extractor before heating. If not, you will undo the hardening of the extractor and it will bend/twist on you...

You want to heat around the bolt (concentrate on the hole around it). I would not recommend hitting it with PB Blaster right after heating, as it will also cool the "hole" area around it, that's where you want the heat to expand it.

You want to shrink the male/stud portion, and expand the female/hole portion. If you cool them down with the penetrating oil, you will cool them together which defeats the point of heating it up. It is best to cool with penetrating oil if the stud is sticking out and you can avoid cooling the hole. Your stud is not sticking out, so I would go at it without cooling it down with penetrating oil after heating.

Heat, put in the easy out, then see if you can back it out.

If it comes out, then see if the threads are ok or not. Try chasing it with a tap and see if it works. If not, you may need to get a Heli-coil kit or similar (Time-Sert like 74dusted recommended) and put it back to the proper thread size.
 
Lol, engine is on a stand... Sharpen a Tig Tungsten & the POS is out in 10 Min with a Tig welder. When you break off the EZ out maybe you will listen.

You guys are funny.
 
bighammer said:
:banghead: As luck would have it I now have a snapped off 9/64ths cobalt bit in one of the exhaust manifold bolts. It's below the surface, and I've gone thru several new 5/32 bits, but it is taking forever, not much progress. :banghead:

Is there another type of bit that is harder than cobalt that I can use?
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All these guys are giving you shitty advise. I would have all your mess out in 10 minutes flat with my technique.
 
Show Off lol nice one , as I said before if I had the tools and ability to do it that way I would . Those valve covers look familiar , where did you get that black breather from ?
 
chryslerfat said:
I agree it looks like you drilled off center. Where you are at now I would blow the rest out with an oxy acet torch and clean the threads with a tap. Being it is drilled through work fast with the torch and you will be shocked how nice it blows out.
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With this method, I'm assuming I would need to pull the head? I may need to anyway, but if not, what about all that slag going into the water jacket?

The bolt is almost completely 'hollowed out" cuz I went after it with a die grinder. I still don't think I am into the threaded part of the head tho. I was able to true up my "off center" hole, but the hole thru the bolt is now tapered. I think I will go after it with the next couple drill sizes until I can get the bolt as thin as possible, then maybe the gas wrench (?)
 
Mad Dart said:
Lol, engine is on a stand... Sharpen a Tig Tungsten & the POS is out in 10 Min with a Tig welder. When you break off the EZ out maybe you will listen.

You guys are funny.
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Well, I don't have a tig welder, but I like your idea, sounds like it may have done the trick for me if I hadn't already committed to the drilling. :banghead:
 
Mig would do it too. You would just need to be more careful is all. My point was drilling
them most of the time has bad results & can compound the problem making it worse than it was before you started trying to fix it.
 
bighammer said:
With this method, I'm assuming I would need to pull the head? I may need to anyway, but if not, what about all that slag going into the water jacket?

The bolt is almost completely 'hollowed out" cuz I went after it with a die grinder. I still don't think I am into the threaded part of the head tho. I was able to true up my "off center" hole, but the hole thru the bolt is now tapered. I think I will go after it with the next couple drill sizes until I can get the bolt as thin as possible, then maybe the gas wrench (?)
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I do it all the time on diesel engines in frame without pulling the head. As much as you have removed with the drill and die grinder already it wont put enough slag in the water jacket to worry about. Just work quick keep hitting the blast lever. The cast head takes longer to heat than the steel bolt therefore working quick will not even damage the head. It works best when you have drilled through as you already have. I learned this way back in the 80`s and have used it ever since with great results.
 
If the bolt remnant becomes only a thin wall hull you can drive a keen tool between it and the head to curl it / collapse it. Afterwards you might need to twist a tap through the hole to clean up scared threads. The end studs are going to get sealant anyway so a small amount of thread damage wont hurt anything.
Next time... Use the exhaust manifold as a guide or pilot for a 3/8 driil bit. Make a true center in the broken bolt. 1/8 deep aint going to hurt anything. There's a slight counter bore on the head anyway.
 
Hey I thought I would update this thread, as I had success with getting the broken off stud out of the head. Here's what I did.

As was mentioned, the hole I was able to make thru the stud was off center because of the embedded (snapped off) cobalt bit, to the point that the Easy Out bolt extractor was starting to grab the threads of the head.

So I got myself a tapered bit for my dye grinder and was able to re-center the hole by slowly, carefully moving the tool to the center of the bolt. Once I was satisfied that it was centered, I had my son 'eyeball' from the side to make sure I was going in at the right angle (I inserted a bolt in the nearest bolt hole to use as a visual guide). I carefully inserted the bit all the way in, the full length of the bolt. Now the bolt is still stuck, but very thin walled, and begging to come out!

I took my tap and, again, had my son eyeball my thread cutter to confirm it was going in at the correct angle. I went in about 1/2" and I could feel it cutting thru the bolt, making threads.

Below is what it looked like when I backed out the tap. All that is left of the broken off bolt was reduced to these "threads"! It all came out in one piece:
 

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The bolt sticking out to the right of the tap is what I used to eyeball the angle of the dye grinder as I pushed it into the bolt.
 

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This is the cheap little dye grinder I used to hollow out the bolt.
 

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Ya gotta admit, the dye grinder did a great job, got the bolt hollowed out to the point that the only thing left was the threads! I was pretty ecstatic when I pulled this out of the head. The head threads remain undamaged.
 

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