How To Use Thread Chasers And Inserts To Repair Stripped Bolt Holes
Stripped bolt holes or screw holes, no matter where you encounter them, can turn a normal repair job into a total nightmare. That's why AutoZone has all the thread repair kits you need to work confidently on your car.
Basically everything in your vehicle is held together by a combination of bolts and nuts. If you are the sort that tinkers a lot with your car, you've probably stripped a bolt before. It is more likely that one of the holes will strip at some point when you loosen and tighten the nuts.
Many people are tempted to try and “make it work” when it comes to dirty or damaged female threads; however, this is not wise. It is better to deal with a stripped bolt hole as soon as you realize it's a problem. Dealing with a stripped bolt hole can be a bit irritating, but it's a lot less irritating than dealing with the damage that one can cause.
Fortunately, dealing with a stripped bolt hole doesn't have to take all that long, particularly if you get a lot of practice with it. The main thing to remember is that if you are dealing with bolt holes around the engine, you want to be very careful about metal shavings getting into the intake manifold. This can end up being an expensive headache if it happens. Best practice here is to avoid using a cutting tap which will remove metal. In these very sensitive environments, you want to consider using a forming or a chasing tap instead. Rather than cutting away metal, these taps will simply reform it.
How to Fix a Stripped Bolt Hole in Metal
If you want to know how to fix stripped threads, it's important to understand what the problem is and how severe it is. In the event that the threads are not entirely destroyed but simply not pronounced enough to grip the bolts, you may be able to salvage the situation with a thread chasing tap. This is the easier of the two options to fix stripped bolt holes, given that the thread chaser will carve away rust and help redefine the threads, but it will not remove or reform the metal. This is very useful in areas around the engine, where manifold intake could be a problem with metal fillings. In reality, this is more like cleaning out the threads rather than entirely replacing them, and you probably always want to try a chaser before moving on to a tap that carves metal out of the hole.
Generally speaking, you will not have a difficult time finding a thread chaser if you need it in a standard size.
Some people will indeed use thread carving taps to clean their threads and not a chaser; however, if you do this you run a higher risk of accidentally widening the bolt hole, which can loosen the grip, causing obvious problems. In sum, if you do have anything resembling a thread left in the bolt hole, it's wiser to use a thread chasing tap. It is always best to try the easiest solution first.
However, in some situations the damage to the threads is too much for a thread chaser to repair. The complete repair for stripped threads is to use a coil-type thread insert. These inserts will give the bolt hole completely new threads which accept the size of the original bolt. In order to use inserts, you must drill the damaged holes slightly larger so that it can take the thread insert.
This guide will focus on how to use coil type thread inserts to revitalize a completely stripped bolt hole.
How to Fix a Stripped Screw Thread with Inserts
Remove the Bolt
The first thing you will need to do is remove the bolt. If the hole is completely stripped and you cannot get enough grip to remove the bolt, you will need to drill into the center of the bolt and have a bolt extractor on hand to remove it.
Clean the Remaining Threads
Once you have removed the bolt, use a clean rag, some compressed air, and penetrating oil to cleanse the remaining threads. If you have a Shop-Vac, it can be very helpful for this process.
Find the Right Drill Size
Examine the drill size that is listed on your coil-type thread insert's package, and make sure that you can drill the bolt-hole to this width. A drill block will help you ensure that the hole you are drilling remains straight. You need to use cutting oil to cover the tap, and occasionally back it up to clear out fillings which can become impacted if this is not done. (Remember that if you are working in a sensitive part of the car where metal shavings can cause major damage that you want to use a forming tap instead.)
Screw the Thread Insert onto the Installation Tool
Next, take the thread insert and screw it entirely into the installation tool. There will be a tab on the bottom of the thread insert, and this will be locked on to the end of the tool if installed properly.
Screw in the Thread Insert
At this point, the thread insert should be covered with a thread-locking compound, so that you can screw it into the new threads. At this point, you should make sure that the thread insert is entirely flush with the surface. Needle nose pliers will be helpful to help you remove the tab on the coil.
After all of this, you should be able to easily replace the bolt into its new hole. It’s important to understand how to replace a stripped bolt hole, particularly if you work with cars frequently, specifically if you work with older cars. Like with many aspects of mechanics, the more you do it the better you will get. Many seasoned mechanics can completely replace female threads in less than 10 minutes.