Log in

Login to your account

Username *
Password *
Remember Me


How to remove a broken bolt and repair damaged threads

  • 03 August, 2018

Few things disturb us more than the bewilderment of a broken bolt or seized pipe plug in a casting. You’re at a loss for how to get the darned thing out. This is when you have to slow down and come up with the best approach for how to get it out without further damaging the casting.

What makes bolts fail? Bolts and screws break off because there’s a weakness in the fastener or corrosion has caused the fastener to seize in the casting. When you’re working with steel fasteners or iron pipe plugs in aluminum castings, the root cause of trouble most of the time is dissimilar metal corrosion (galvanic corrosion). Galvanic corrosion is where two very different metals develop an unpleasant attitude with each other. This is why it is important to lube bolt and pipe plug threads during assembly to prevent future trouble.

What causes galvanic corrosion in fasteners, plugs and castings? If conditions are dry you’re less likely to experience galvanic corrosion. When conditions become wet, civility between dissimilar metals goes off the rails. Fluids such as water and acid serve as electrolytes to create an electrochemical reaction between dissimilar metals. Salty air is another culprit and highly corrosive. Electrons begin their journey from one metal to the other and metals begin to breakdown. When a fastener and casting have been secured together for years and exposed to the elements, failure of the fastener is inevitable.


There’re also stress issues that go with fasteners because they’re under considerable tension for a long period of time. Stress corrosion comes from exposure to the atmosphere, loading, tension and cyclic fatigue. Engine, driveline and chassis components are subjected to extreme loads and the resulting cyclic fatigue. This is another reason why bolts and screws fail and break off. Engine fasteners, as a prime example, experience a tremendous amount of stress and heat cycling. And this is why they’re prone to failure in some applications.

There’s always much we can do to prevent fastener failure by conducting proper installation to begin with. Bolt threads should be lubricated during installation to reduce stress and achieve an accurate torque reading. ARP bolt lubricant should always be used when you’re installing fasteners because it yields a proper torque reading without stressing the fastener.

Bolt, screw and plug extraction need not be difficult if you’re patient and think the process through. If the fastener or plug cannot be driven out with a punch or chisel, you will have to drill it out in phases until it can be removed with an extractor. Sometimes heat has to be applied to the area around the fastener or plug, which causes the area to expand and loosen up. Soaking the area with penetrating lubricant days ahead of time offers some hope, and reduces the likelihood of failure.

Thread Repair

What happens when a broken bolt or screw extraction turns into threads damaged beyond repair? Damaged threads can sometimes be chased and cleaned up with a thread chaser or tap. When they’re damaged so badly they cannot be cleaned up, your only choice is to drill them out and replace them with a Heli-Coil insert or a Time-Sert. The difference in these threaded inserts is both convenience and cost. The Heli-Coil insert is the more affordable of the two and more easily found. Time-Sert is an incredible innovation and, therefore, more expensive. Both thread repair types are available from Summit Racing Equipment.

When you are performing thread repair or replacement you must be patient. Make sure you’re using the right-sized drill bit for the damaged hole. The drill bit must be parallel to the hole. You may use a straight edge or a precision steel block as a guide, not to mention a drill press and a vice if the part can be removed from the vehicle. Always confirm accuracy before the drilling begins. Get this wrong and your troubles are only beginning.

Once you have drilled the damaged threads out, remove all the debris from the hole. When you don the correct-sized Heli-Coil tap, lubricate the threads with a Permatex Fast Break Super Penetrant and slowly run the tap. Run the tap a full revolution and slowly back out one-half turn to clear debris. Continue running the tap until threads have been cut the full depth of the hole. Wash the hole out with brake cleaner and allow it to dry.

The Heli-Coil insert is screwed into the tapped threads until seated. It is suggested you use Permatex Threadlocker on the outside diameter of the Heli-Coil insert to ensure security. Once the Heli-Coil is seated, break the tang off and you’re ready for assembly.

1. How easily a broken bolt or screw comes out depends on why it broke off to begin with. If bolt breakage is due to material failure, the remains should be easy to remove with a chisel or punch, as shown.

2. When a bolt becomes seized in the casting or forging, you’re going to have to drill it out. Bolt extraction begins with a small pilot drill mark to get the drill bit and bolt extractor centered.

3. Ideally, you will use a titanium drill bit to cut into the fastener. Drill at a low speed with mild pressure and allow the drill bit to do its work. We’ve begun drilling with a 1/8-inch bit to get started.

4. Your drill bit should get progressively larger as you go until you’re near the full diameter of the bolt, without getting into bolt threads.

5. This is about as far as you should go size wise. We didn’t get our extractor hole as dead center as we would have liked. The darned thing looked centered when we started.

6. The bolt extractor is a left-handed coarse thread tool that screws into the hole as shown. Carefully turn counterclockwise and attempt to remove the broken fastener. You do not want to break the extractor off in the fastener because you will never be able to drill the two out. If the extractor requires a lot of force to turn, apply heat to the area around the bolt and try again.

7. We were able to extract the fastener and wound up with clean threads.

8. This is a thread cleaner, sometimes called a thread chaser. Using a penetrating lubricant, run this into the bolt hole and run it back and forth until it turns smoothly.

9. We decided to chase all of the bolt holes in this LS crankshaft to ensure cleanliness. It is a good practice to chase all bolt holes in a given installation, then, use a thread lubricant as a preventative measure.

10. Run the thread cleaner/chaser as far as it will go into the hole and run it back and forth. Flush the hole out with brake cleaner. Use antiseize on bolt threads.

11. Spark plug holes can be problematic, especially in aluminum cylinder heads. Whenever you have to chase and clean up spark plug holes, use a penetrating lubricant and make sure the piston is near top-dead-center to prevent cylinder wall damage.

12. Run the thread chaser/cleaner back and forth until it turns smoothly. Blow out the spark plug hole with compressed air, using eye and face protection. Ideally, you will have the exhaust valve open to allow any debris to escape.

13. Don’t waste your money on cheap drill bits. Spend the money and opt for titanium or cobalt drill bits, which are harder, coated and will outlast the low-buck stuff. And when you drill, run the drill at low speed using a good penetrating lubricant. Keep your drill bits sharpened to where you can use them again and again.

14. The OEM Automotive Tools Bolt Extractor Set from Summit Racing Equipment offers you a variety of sizes for a broad range of applications you may encounter. The Bolt Extractor Kit includes five mechanics length right-hand cobalt drill bits and five tapered chromoly left-hand thread extractors. This is all you’re going to need for most fastener extractions.

15. Summit Racing Equipment offers a wide variety of bolt extraction options, including Bust-N-Out (PN SUM-902-375) for 3/8-inch, 16, 24, and M10 applications. There are many other sizes available from Summit.

16. More challenging than bolt extraction is the removal of a steel pipe plug in an aluminum casting, which is a corrosion nightmare. It’s virtually impossible to remove an iron pipe plug from an aluminum casting. We get into trouble because we screw the iron pipe plug right into the aluminum, which corrodes over time and seizes. Removal begins with the drilling of a 1/8-inch pilot hole to get started.

17. A larger 5/16- or 3/8-inch bit is used next to get the extraction hole closer to the plug’s outside diameter. The objective is to weaken the plug for easier extraction. And a word to the wise, never use iron pipe plugs in iron or aluminum castings. Use brass. Wrap threads with Teflon tape as a protective barrier.

18. The aluminum casting is heated around the pipe plug to help the aluminum expand around the plug. However, you must be very careful with heat and not use too much of it. Too much of it and you can distort and even melt the aluminum. Apply heat and give the extractor a counterclockwise twist.

19. A stubborn pipe plug gets treated to dry ice after heating the surrounding area with a torch. The extremely cold dry ice makes the pipe plug contract in the hole.

20. With the pipe plug drilled out to near its outside diameter, the wall is weakened enough to get the plug out. Now is the time to chase all thread ports and bolt holes in the casting. Use Teflon tape or sealer on pipe plugs during installation.

21. Harbor Freight’s Warrior pipe nipple extractor set is engineered to free pipe nipples from castings and fittings without cracking, marring or scratching. These high-quality pipe nipple extractors are made of durable, heat-treated steel and feature zinc plating. Keep a set of these on hand for weekend emergencies.

22. Summit Racing’s Performance Tool five-piece bolt extractor set removes stubborn nuts and bolts from iron and aluminum castings. What makes these extractors work so well are the gripping internal surfaces that remove rusted, rounded or painted nuts and bolts regardless of size. These high-quality sockets are manufactured from chrome molybdenum steel.

23. Heli-Coil inserts from Summit Racing Equipment are the industry standard for thread restoration because these threaded inserts work in any material: aluminum, magnesium, cast-iron, bronze and a host of others. Damaged threads can be restored to better-than-new condition in spark plug holes, carburetor fuel inlets, transmission and engine castings, oil drain plugs, exhaust and intake manifolds, cylinder heads, brake calipers and suspension components.

24. We were at Burbank Speed & Machine assembling a 489ci big-block Chevy when the head torqueing process turned into stripped threads in a wet-deck bolt hole. Dave Akard of Burbank Speed examined the hole and concluded it needed a quick fix with a Heli-Coil insert. Dave also had a Time-Sert kit on hand, which is an even better solution because the threaded inserts are solid machined pieces that screw into the existing bolt hole.

25. Dave took a 1/2-inch titanium drill bit and cleaned up the hole to get it ready for tapping and a Heli-Coil insert. Dave stresses patience and accuracy when drilling a damaged bolt hole out. Get the bit parallel with the hole and slowly drill out the damaged threads.

26. With the bolt hole drilled out, Dave applies negative pressure (vacuum) to the hole to extract any debris. Compressed air is also effective. Use face and eye protection.

27. Dave has applied a sparse amount of penetrating lube to the Heli-Coil tap and is cutting fresh threads into the iron deck. He uses a precision steel block to ascertain alignment of the tap. The tap is screwed in one full turn and backed out one-half turn to clear debris. Dave ultimately runs the tap as far as it will go and backs out.

28. This is the appropriate Heli-Coil threaded insert, which will be screwed into the threaded hole until it is just below the block deck. The Heli-Coil installation tool grabs the tang (not visible here) and screws the insert into the threaded hole. Once seated, the tang gets broken off, opening up the bolt hole. You may use Permatex’s Threadlocker on the outside threads for added security.

29. The Heli-Coil threaded insert is screwed into the hole and run down as far as it will go. Once seated, the tang used to screw the Heli-Coil in will be broken off and discarded. It is suggested you use a thread locker on the outside of the insert for security.

 30. The Heli-Coil insert has been seated and the tang broken off to make way for the head bolt. Be very careful installing the Heli-Coil insert. It is easy to jump threads and not recognize you’ve missed a thread. Slowly and methodically screw the Heli-Coil into place, then check the installation with the bolt. If the bolt binds up, the Heli-Coil is incorrectly installed.

 Time-Sert is another excellent thread repair option, which does not employ coiled threaded inserts, but instead, a solid insert that screws into the threaded bolt hole.

Source: Superchevy

Contact us about our precision machining capabilities.......

Tien Po International Limited

Dongguan Tien Fai Metal Manufactory

Corporate Office

  • Room 2105, Kodak House II, 39 Healthy Street East, Quarry Bay, Hong Kong
  • (852) 2557-3139
  • sales@tienpo.com.hk
  • (852) 2897-0879


  • Hung Lee Industrial District, Mao Bin Management Area Town of Liao Bu Dong Guan, Guang Dong Province
  • (86-769) 8332-1027
  • sales@tienfai.com.cn
  • (86-769) 8332-8976
Copyright © 2021 Tien Po International Limited