How to Drill Out Broken Bolt in Engine Block (5 Steps)

With this how-to guide, you’ll learn how to drill out the broken bolt in an engine block.

The engine block is the worst possible location to have a broken bolt. Many people try several methods to extract the broken bolt before giving up. I can tell you through experience that with a drill and bolt extractor kit, you can do a great job and ill teach you how.

In general, to drill out a broken bolt from the engine block:

  • Clean the surrounding of the broken bolt.
  • Wear safety gloves and glasses.
  • Mark the center of the bolt with the center punch.
  • Drill the center of the broken bolt.
  • Use the screw extractor to pull out the broken bolt.

I’ll go into more detail below.

5 Step Guide – Getting Started

Things You’ll Need

  • Drill with drill bits
  • Manual or automatic center punch
  • Hammer
  • Safety gloves and glasses
  • Bolt extractor kit
  • PB Blaster or WD-40 for lubrication

Step 1 – Clean the Surroundings

First, examine the surrounding area of the broken bolt. You are performing this inside an engine block. So, there might be some dust and debris on the broken bolt. Clean the surrounding area properly. Also, remove any objects such as cables that might bother you while drilling.

Step 2 – Wear the Safety Gear

Then, wear safety gloves to protect your hands. Wearing safety glasses is a must. Always remember, in this process, you are drilling a metal bolt. Small metal pieces might hit your eyes.

Step 3 – Mark the Center of the Broken Bolt

Next, you’ll have to mark the center of the bolt. You can use the center punch for this. When it comes to center punches, there are two types.

  • Manual center punch
  • Automatic center punch

If you are using a manual center punch, you’ll need a hammer to punch it. Position the center punch on the center of the bolt and tap it with the hammer. One good tap is more than enough to mark the center.

On the other hand, automatic center punches work a bit differently. For starters, you don’t need a hammer. These automatic ones come with a switch. Position the center punch on the center of the bolt. Press the switch to punch the center on the broken bolt.

Some automatic center punches lack the punch to create a good center mark. When that happens, position the manual center punch over the marked center and punch it again.

Tip of the Day: During the bolt extraction process, marking the bolt’s center is much more important than one might think. So, try to find an accurate center.

Step 4 – Drill the Marked Center

Now, you can start the drilling process. But first, you’ll have to choose the right size drill bit for this. What do I mean by right size?

  • The diameter of the drill bit should be less than the diameter of the bolt.
  • Try to choose a drill bit that matches the size of the screw extractor that you plan to use. You’ll get a better idea about that from the next step.

Then, insert the drill bit into the drill and start the drilling process. Keep the drill bit on the center of the bolt. Apply some WD-40 if needed. It will help the drilling process.

Step 5 – Use the Screw Extractor

After drilling an enough-sized hole on the bolt, move on to the bolt extraction.

  1. Choose a suitable-sized bolt extractor from the bolt extractor kit.
  2. Insert the screw extractor into the bolt hole.
  3. Hammer it lightly.
  4. Turn the bolt extractor counterclockwise. Use the small spanner for this.
  5. Steadily rotate the extractor and pull out the broken bolt. 

Be mindful: Drill bit extractors are used for extracting broken bolts and screws. They are threaded in a counter-clockwise direction.

Make sure you don’t break the bolt extractor inside the bolt hole. If that is the case, you might have difficulty pulling out the broken bolt. These drill bit extractors are made with hard metal. Hence, drilling them won’t be an easy task. (1)

Tip: You can also use a mole grip instead of the screw extractor.

Few Other Ways to Pull Out the Broken Bolt

The above 5 step guide is the quickest and easiest way to pull out a broken bolt from the engine block. But it is not the only way. Depending on your skill level, knowing another technique might not be a bad idea. So, here are some alternatives for the above method. (2)

  • Drill the bolt using a left-handed drill bit.
  • Welding on the broken bolt.
  • Break the rust on the bolt and get it out.

FAQs

What Direction Do I Turn a Screw to Loosen It?

Most bolts, screws, nuts, and lids tighten clockwise. So, you can loosen them by rotating them counterclockwise.

How Can I Pull Out a Broken Bolt by Using Only a Drill?

Find a left-handed drill bit if you don’t have a screw extractor kit. The left-handed drill bits rotate in a counterclockwise direction. Thus, while drilling, the bolt will get loose automatically. However, the process is a bit more difficult than using a screw extractor. Also, you’ll have to use a drill that has reverse gear.

Why Do I have to Use WD-40 While Drilling Out a Broken Bolt?

You don’t have to use WD-40 for every bolt extraction. Only use WD-40 to remove corrosion and rust.

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.