Extracting bolts

Last Updated on July 22, 2024 by Mutiara

Extracting bolts

A collection of successful extractions.

Oops! You suddenly find yourself with wrench in hand, the head of the bolt you were trying to extract bouncing on the floor, and the rest of it still in the cylinder head/engine block/suspension piece.

Congratulations – you’re about to have an adventure.

I recently ran across a collection of my “adventures” that, I just recently realized, had collected in a tray in the top drawer of my tool chest. Seems I tend to keep the broken pieces as mementos of my battles … er … adventures. You can get the remains of a broken bolt, stud, tap or extractor out without a major hassle, but as I’ve learned the hard way, it’s better to learn from others than to learn from your own mistakes (the definition of wisdom, by the way).

Have you ever twisted the top off the last remaining portion of a protruding bolt, only to be faced with the option of drilling? Or have you ever had an EZ-Out strip out the drilled hole, unable to “bite” any of the surrounding metal? In the following paragraphs, I will share great tips using my own experiences, as well as suggestions from techs who posted on the International Automotive Technician’s Network (iATN) regarding this subject.

But first, a little science …

An off-center drill.

Have you ever used heat to help remove a fastener? Richard Lindwall of JEMCO in Oakland, Calif., shares an awesome tip on how you can anneal steel by heating and cooling your work piece. We’ll visit this topic before discussing other procedures, because this critical decision can make the difference between a quick extraction and destroying the part you’re attempting to save.

“When you heat the fastener you are going to drill, anneal it and don’t harden it,” writes Lindwall. “If you anneal the material you are going to drill, your drill won’t have such a hard time trying to bite it and it will cut easier. Also though, if you anneal it and it is truly stuck, you will have a much harder time turning it out without it twisting or breaking off. If you know it is a bolt that you’ll drill to the end, anneal it. If you will drill to the point of extraction with pliers or an extractor, harden it.”

Two dead-center drills; two off-center.

My research bears out Lindwall’s statement. Annealing is the process of subjecting metal to heating and cooling to toughen it and reduce brittleness. Full annealing is the process of raising the temperature to a specific point, then letting the metal cool to room temperature. This changes the grain structure, making it softer and easier to drill.

Lindwall describes his process of annealing and hardening: “Use a carburizing flame and thoroughly coat the area to be annealed with a thin layer of carbon. Change to a neutral flame and heat the stud or bolt (keeping the flame back from the part) until the carbon is burned off. Walk away and have a coffee or something and let the part slowly cool to room temperature,” Lindwall said. “Use a sharp bit and it will drill like iron. If you are just going to grab a stud with your vise-grips, heat that baby to a bright red. Then cut your flame. Just as the red goes dull, hit it with something to cool it, such as water.” Lindwall said this will harden the stud, which is good if you don’t want your extractor shaving out the middle or your vise grips carving down the outside. It also loosens rust bonds that form on exhaust studs.

Best case scenario

Left-hand drill bit and corresponding extractor.

In my opinion, if you’re left with a piece protruding from the surface, you’re lucky. In this situation you can harden the stud and grab it with locking pliers, or you can build a new bolt head.

Find a flat washer with a hole size the same or just a little smaller than the broken bolt. The washer needs to be close to the broken-off bolt and if the bolt is broken off beneath the surface, a ball peen hammer can be used to “dish” the washer to make it fit close to the bolt.

Weld the washer to the bolt. I prefer using a wire welder because it is easier to see what you are doing; plus, on smaller bolts it is difficult to avoid melting the washer with the higher heat of a stick welder. Once the washer is securely welded to the bolt, weld a nut to the washer. The nut should be the same size as the broken bolt head or larger, depending on the outside diameter of the washer. Weld to the outside flats of the nut, grab a wrench and it should screw right out. If not, repeat the process. The washer is the key to this trick working right as it is very hard to get adequate penetration trying to weld down inside a nut by itself. Also, welding the washer first concentrates the heat on the bolt and this heat helps loosen the bolt.

I use this same method on pan-head fasteners that are flush with the surface, that have a stripped-out internal Phillips, torx or hex head. But usually, I can successfully turn these out using a cold chisel and a hammer or a few quick blasts from an air hammer with a sharp chisel bit. Vibration is a key to getting these out.

Broken below the surface

A welded nut on top of a broken stud to remove it.

When dealing with a fastener that needs to be drilled, then extracted, the most important step is to get a hole drilled into the center of the stud. The center punch is crucial to your success. If it is off center, so will be your pilot hole and all of those thereafter, and the end product as well. Sometimes I eyeball it, and sometimes I use the sized pilots that come in extractor sets. However you do it, this is the single most important step and great care should be taken to be as accurate as possible. If the broken piece is not flat, I pass a hand grinder over the rough top surface to give myself something flat to center punch, and then start drilling. Use penetrating oil for the lubricating and cooling effects.

Jerry Wooldridge of Seattle, Wash., shares some great drilling tips once you have a good center punch and it’s time for a pilot hole. He starts by reminding techs that the less material you are trying to remove at once, the less likely the drill will wander around. Using a good sharp bit of a small (1/8-inch or below) size, drill a hole straight down the center of the offending bolt, he writes. “Be sure to use the drill stops! You don’t want to drill deeper than the broken piece. Take your time, and keep the drill speed and tip pressure at a point where you are cutting cleanly and steadily,” said Wooldridge. “This will vary according to the type of stock being drilled. Hardened steel is tough, every time.”

After your pilot hole is sunk, start enlarging the hole a couple of bit sizes at a time. Bits cut more cleanly this way, and this gives you more control. Be sure to inspect your work often with a mirror and flashlight (tip: point the flashlight into the mirror).

If you’re very lucky, the heat and vibration of drilling will break the bond. This is why you want left-handed bits – if this works, you’ll pull the piece out, rather than driving it further in.

Robert Jenkins of Michigan, another iATN user, suggests using a good SLOW-speed, high-torque drill. A half-inch tool truck drill is great. If you go too fast you will trash ANY bit. About 500 rpm should be max.

Now that you have a good-sized hole, try an extractor. There are two sorts – straight fluted and twist fluted. I prefer the straight ones because all the force is used to turn the broken stud, rather than twisting the extractor in farther. But the twist extractors are more amenable to weird hole sizes. Don’t break it off, whatever you do.

Heat the area with the heat wrench (without the extractor in the hole), spray on some penetrating oil and wait. Repeat several times. Try the extractor again. Repeat until you’re frustrated and ready to go on to the next step or, if you’re terribly lucky, the blasted thing comes out. The hotter the torch the better – try to get the part red hot.

There is a new generation of tools that combine a left-handed drill bit and extractor and even claim to center themselves. They might make this job a little easier.

If you’re now to the point where the extractor won’t work (it feels as though it’s going to snap, or it’s stripping-out in the hole), use the next larger drill bit. Continue drilling larger holes until only a thin shell remains. Using mirror, flashlight and Dremel tool, grind outward from the hole you’ve drilled. Eventually, you will start to see the ridges of the thread cut into the head poke through the stud material. At this point, you can try using the hammer and punch to rotate the fractional piece of the stud in the threads. Or you can keep drilling until only the threads remain, then you can use a scribe to pick the pieces out of the troughs of the thread.

If the piece won’t rotate, I get to a point where either I can take a punch and collapse the bolt threads inward, then pull it out with needle-nosed pliers (usually in blind holes) or I can go just until I see the tops of the threads and run a tap through (if it’s an open hole such as at an exhaust flange). If it seems as though this won’t be possible, I go ahead and reach for a heli-coil at this point. They’re great, they work, and you aren’t out to prove anything here except that you can repair it right in a sensible amount of time. Quite often though, I find that by progressively enlarging the hole, the stud weakens and comes out by one of the above methods.

When you have achieved this state, you can start using the tap to remove the remaining metal. Best is a tap with a tapered start, so you can get some purchase in the hole you’ve drilled. Once you’ve removed a bunch of the metal, you can switch to a plug-style or bottoming tap to clean out the deeper grooves. Chances are that the trapped material will break off in complete rings, which you want to remove – pull the tap and use a sharp object to try to clear these out before tapping more. You want to reverse the tap often to clear the shards. Use the tap to essentially tap a new hole – you want to go about one-eighth turn at a time, cleaning the tap every time.

Worst case scenario

A collection of broken extractors and a broken bit – all remained in the piece that was to be removed.

So you broke off the extractor or the tap? OK, repeat after me: “*#@!&*!”

There now, don’t you feel better?

If you’re good with a welder and you’re brave, you can try welding a piece of stock to the broken bit to give yourself some purchase to turn it out.

If you have a plasma cutter, you can attempt to dissolve the tap or extractor yourself, or you can take the part in question to a machine shop that has a plasma cutter or an electrical discharge machine (EDM) and get them to remove the remains. They’ll cut the extractor or tap out in nothing flat, very precisely.

A set of thread repair tools.

Tap extraction is the process of electrically disintegrating a broken tap, drill, bolt, screw or pin. An alloy tube of various sizes is lowered drill-press style onto the broken component. An electrical current then disintegrates the broken component until it crumbles and can be chipped out, leaving the threads/hole undamaged.

You can find such businesses on the Web or in the Yellow Pages.

How to avoid broken bolts

When you finish repairing a hole, make sure you use anti-seize on the new studs or bolts before you install them, so you (or the next tech) won’t have to go through this the next time. On exhaust parts, use brass or stainless steel nuts and lock washers, so they don’t corrode in place.

This article was written by Brian Manley who is a vocational automotive instructor for the Cherry Creek school district in Aurora, Colo. He is an ASE master certified automobile technician and a former member of the National Automotive Technicians Education Foundation (NATEF) board of trustees. He can be reached at [email protected].