How to Easily Retap a Bolt Thread on Your Subaru Engine: Expert Tips Inside

Subaru cars are renowned for their durability and reliability, but even the most well-maintained engine can develop a stripped or damaged bolt thread. Retapping a bolt thread is a crucial skill that every DIY mechanic should have under their belt. If you’re a Subaru owner with some experience working on engines, this guide will teach you how to retap a bolt thread on your Subaru with ease and precision.

Introduction to Retapping a Bolt Thread

A stripped or damaged bolt thread refers to a metal bolt that has been twisted or broken off during installation. This can happen if the bolt is overtightened or due to wear and tear over time. Retapping is the process of restoring the damaged thread by cutting a new thread into the existing hole. This method is inexpensive compared to replacing a whole part.

Tools Needed for the Task

Before you begin retapping, it’s essential to have all the necessary tools at hand. Here are the tools you’ll need:

  • Retapping tool kit (size specific to your bolt thread)
  • Drill bit
  • Lubricant such as cutting oil
  • Safety gloves
  • Safety goggles
  • Threading Tap

Safety Measures to Take Before Starting the Retapping Process

It’s crucial to prioritize safety when dealing with any car engine activity, and retapping is no exception. Here are some measures to take:

  • Always wear protective gloves and goggles while retapping to prevent metal chips and debris from getting into your eyes or hands.
  • Ensure that the car is parked on a level surface
  • Disconnect the battery cables before starting the process to avoid electrocution or electrical damage
  • Avoid wearing loose clothing or jewelry that may get caught in the machinery.
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Step-by-Step Instructions on How to Retap a Bolt Thread in a Subaru Engine

  1. Identify the damaged or stripped bolt thread and determine the size of the retapping kit needed.
  2. Remove the bolt from the thread using a wrench or pliers and clean the surrounding area with a degreaser or cleaning solvent.
  3. Use a lubricant to apply onto the damaged thread to reduce friction and to reduce the build-up of heat during the retapping process.
  4. Affix the appropriate size drill bit into the retapping tool, then lubricate it properly with cutting oil.
  5. Gently insert the drill bit into the damaged bolt thread and slowly rotate the drill to cut new threads into the existing hole.
  6. Once you have finished drilling, remove the damaged drill bit and replace it with a threading tap of the appropriate size. Again, lubricate the tapping tool before use.
  7. Slowly insert the tool into the drilled hole, making sure to stay in alignment with the existing thread. Continue rotating the tool until you have cut the required number of threads.
  8. Remove the threading tap and clean the area of debris and oil residue.
  9. Reinstall the bolt into the retapped hole and tighten it.

Common Mistakes to Avoid While Retapping a Bolt Thread

  • Over-tightening the bolt can lead to damaging the thread again. Always refer to the car’s manual for the recommended torque specification for each bolt.
  • Using the wrong size retapping kit or drill bit can make the retapped thread too large, which can lead to bolts falling out or not fitting securely.
  • Failing to lubricate the drill bit or the threading tap can cause heat buildup during the retapping process and damage the bolt’s threads prematurely.
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Post-Retapping Cleanup and Inspection

After you’ve installed the bolt back, clean up the surrounding area to avoid the buildup of metal shavings and debris. Double-check your work for any abnormalities, and make sure the bolt is secure. A stable bolt ensures that the engine’s efficiency is not hampered.


  1. How long does it take to retap a bolt thread?

The length of time it takes to retap a bolt thread depends on the size of the bolt and the severity of the damage. Typically, the process should take between thirty minutes to an hour.

  1. Can I retap a bolt thread under all circumstances?

Not all bolt threads can be retapped. Threads that are extensively damaged or completely stripped cannot be retapped.

  1. What happens if I overtighten the bolt after retapping?

Over-tightening a bolt could damage the threads and negates the retapping process, leading to further damage. Refer to your manual for recommended torque specifications.

Final Thoughts

Retapping a bolt thread is a crucial skill that every Subaru owner should have under their belt. Knowing how to do this yourself can save you time and money on repairs. Remember to prioritize safety when doing any engine work on your vehicle, and if you’re not sure whether retapping is the right option, consult a qualified mechanic.

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Alton Brobst

As a longtime Subaru enthusiast, Alton brings a wealth of knowledge and experience to our blog. From his early days of tinkering with engines to his current role as a certified Subaru technician, Alton has seen it all when it comes to Subarus. When he's not working on cars, he enjoys hiking and exploring the great outdoors.

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