Dear Ole Mechanic;
I have followed and enjoyed your column for some time, and I can tell that you work on old stuff from time to time. That means that you have dealt with a problem that I run into all too often, even if it has only been once. That is a broken off bolt or stud in a blind hole. What is your favorite way to get a broken bolt out? I am currently looking at one that also has a broken easy-out in it, and I am at a loss as to how I can save an old engine block. The block is old enough that replacing it is out of the question. It is not the cost of replacing the block, I can not find another one! Any words of wisdom would be greatly appreciated.
Out It Ain’t
I will tell you right up front that I do not like those so-called easy-outs. The only time that I will dig out my set is when the broken piece is loose enough to be turning in the threads of the hole. OK, so much for my running down of easy-outs. Now, to your problem of a broken easy-out. As you have probably figured out, an easy-out seems to be harder than a diamond, if you have tried to drill it out. That fact can work to your advantage. In the past I have taken a good quality drill bit and sharpened it into a small chisel. Then using a hammer I have been able to break up the easy out into small pieces and dig them out. DO NOT use safety goggles. Use a FULL-FACE safety shield, as small bits of easy-out and the home made chisel are going to chip out at somewhere near the speed of sound. I have had to dig a chunk out of my face just below my lower lip. If you have ever seen a dog ‘passing’ barbwire out of its backside, you will get a good idea of how I was quivering and feeling as I pulled it out. OUCH! Use a full-face shield. Once you use a small magnet to get all of the easy out pieces out, then you will be able to proceed with my preferred way of removing a broken bolt. I am going to go all the way through what I do. You can ignore the first part and pick up what you need to do at the ‘enlarging the hole’ part.
First, get things out of the way so that you can see and work around the blankeity-blankin’ piece of bolt. Use a hammer and center punch to get a starting point to drill a small hole all the way through the center of the bolt. If your center punch mark in not in the center, try again because you need to be in the center for this method to work. Then, carefully drill a small hole all of the way through the bolt. Take your time and make sure that you drill straight through. Now, take your favorite penetrating oil and get some through the hole that you just drilled. Next comes my personal secret--my set of left-handed drill bits. Left-handed drill bits must be turned backwards to drill. That is in a counter-clockwise rotation. Using left-handed drills, start drilling the small hole a little larger a little bit at a time. If you are lucky, by the time you are using the second drill bit, it will dig in and unscrew the broken bolt out of the hole. It seems that the heat generated by the drilling combined with the penetrating oil will often loosen things just enough that the bolt will unscrew. If you try using regular right-hand drill bits and things come loose, you will just screw it in tighter. If it doesn’t come loose, then continue making the hole larger until you get out to the tap size of the bolt. As long as you were centered with your drilling, you can now run the correct size tap into the hole to clean out the original threads. It is just like tapping threads into a new hole.
This works for me about 90 percent of the time. But what about the other 10 percent when it doesn't work? Say, for example, you didn’t get exactly in the center when you were drilling. If that is the case, there will be a point when you are enlarging the hole that you will start to see threads in one side of the hole and not the other side. Now it is time to dig out that real small hobby grinding tool and start grinding away the bolt until you see threads all the way around the hole. Then run the correct-sized tap down the hole to clean out the original threads.
Now, sometimes with all of the chiseling out of the easy out, enlarging the hole or grinding the darn hole, it gets just too messed up to get the bolt to hold anything. That is just the same as if you had stripped the threads. It is not a problem, as I use a Heli-CoilŪ thread kit. By using the oversized drill, tap and stainless steel thread inserts supplied in the kit, the original-sized bolt will now work just fine.
There are other ways to remove broken bolts, easy-outs and taps, but I will not get into the expense or finding an EDM (Electrical Discharge Machining) machine. If you think my procedure is a little tedious and time consuming, you can always renew your search for another block.
Herr Professor Nuzanbolts