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.
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.