Stripping a bolt hole or a nut’s threads usually make an easy repair very difficult. This usually happens when you over-tighten either a nut or bolt. The friction and force cause the threads to be damaged. And this causes the structure of the bolt to be damaged.
Bolt holes can occur mostly in cars. Since the entire car, including the internals, are held together using bolts and nuts, stripped bolt holes are very common. Every time something is unbolted and put back together, there is a chance of stripping threads.
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Aluminum parts usually get stripped bolt holes due to it being a soft metal. Other metals can also get them due to wear and tear. However, the good news is that these stripped bolt holes can be repaired. There are a few ways to do this. They range from extensive repairs to quick fixes. Let’s go through them all.
Fixing Stripped Bolt Hole in Aluminum
The few tools that you’ll need for this are a cut tap, and a tap handle. You should also have standard measuring tools like a micrometer screw gauge, or vernier calipers for accurate measurement.
Start by determining the hole that has the stripped screws or the bolt hole. Then determine the size of the thread. All threads are characterized by their outer diameter, their dash, and the thread count.
To determine the hole’s outer diameter, you can measure the width of the screw or the bolt. To get an accurate reading, use a micrometer screw gauge, or vernier calipers. You’ll get a much more accurate reading than if you use a scale or a ruler.
Then determine the thread count by simply counting the threads in an inch of screw length. First, count all the threads, and measure the length of the screw with threads. Then use ratios to determine how the thread count (bolt length: number of threads=inch: thread count).
Use the tap attached to the tap handle over the stripped bolt hole. If the hole was made by right-hand screws, insert the tap into the hole while rotating it clockwise. If it’s a left-hand hole, rotate anti-clockwise. Nearly all holes, screws, and bolts are right-hand screws; however, there can be exceptions.
Rotate the tap handle completely two times. Then do a quarter of a counter-clockwise turn. Make sure you repeat the process until the tap handle can’t be rotated easily.
After step 3 is sufficiently repeated, rotate the tap handle counterclockwise. Do this until the tap is out of the hole.
Using Thread Chasers to Repair Stripped Bolt Holes
One of the best ways to fix a stripped bolt hole is to use thread chasers. This is a skill that anyone can master. It’s a quick fix and a permanent fix.
These can be used in the case that your threads aren’t destroyed completely. These thread chasers, along with a thread chasing tap and some grease can do the trick. The thread chaser will clean away the rust and the muck that crowds the bolt hole. These don’t move any metal from the hole. It’s helpful to apply the thread chaser in places like the engine, where loose filings can cause damage.
These are for when the thread damage is total. You can fix stripped threads with coil-type inserts. These inserts provide a newly threaded hole. They accept the original sized bolt. Inserts are usually installed by drilling the damaged stripped bolt hole. This makes the hole slightly bigger, with a larger tap.
These are the tools you’ll need:
- Penetrating Oil
- Bolt Extractor
- Compressed Air Source
- Shop Rags
- Hand Tools
- Electric Drill
- Drill/tap alignment block
- Thread Repair Kit
- Thread Locking Compound
The first thing you’ll have to do is remove the bolt. To do this properly without causing more damage, you should drill the center and use a bolt extractor.
You should then clean the threads on the bolt hold with penetrating oil. Besides the lubricating effect of the oil, this also cleans the hole and gets rid of filings. You can also use a shop-vac for this.
Next, drill the bolt hole which is oversized for the tap. Drill sizes are mentioned in the package. You can use a drill block in order to straighten the drilled hole. Make sure that you’ve kept the tap coated with cutting oil. Also, back the tap up so that you can clear it of any metal filings. If you’re working in an area where the filings can infiltrate the engine, you’ll need to be very careful.
Next, screw the head insert into the installation tool. At the bottom of the thread insert, the tab should be engaged at the end of the tool.
Finally, coat the insert of the thread with a locking compound. Screw the insert into the newly tapped threads until it is locked into the sealing surface. Use needle-nose pliers so that you can snap off the coil’s tab.
Remember that this is a slow process. You won’t get anywhere if you hurry. This is a process that requires precision and care above all else. If you hurry, you may make things worse. Filings can fly everywhere and they can also cause damage to the engine. Know that the process will take time, but will apply a permanent solution to the problem.
Tips for Types of Stripped Bolt Holes
Partially Stripped Threads
These stripped bolt holes can usually stand the normal vibrations of a car. However, when maximum torque kicks in, the bolts begin to come loose. Partially stripped bolt holes occur many times when the bolt is over tightened.
Badly Damaged Threads
These can be recognized by bolts that loose grip very easily after light vibration or moderate torque. Repair methods can vary. Chemical thread filler can be used to great effect here. Thread insert methods are also very effective.
Know that repairing this sort of hole requires a lot of care. You shouldn’t drill the hole deeper than the original depth. A feeler gauge can measure the depth of the hole for greater accuracy.
Thread Locking Material
Thread locking material is used on a stripped bolt hole which is made bigger through a thread tap. Hence, the original bolt won’t fit perfectly inside. The thread locking material forms a permanent bond between the bolt and the hole. This makes it less likely to come loose through vibration. In fact, it stops the vibration process in its tracks.
If you follow these helpful tips and suggestions, you’ll be able to repair stripped bolt holes easily. Just remember to proceed with care and caution.