A spark plug blow out can be a frustrating and unexpected issue, often leading to reduced engine performance or even a complete breakdown if not addressed promptly. This problem occurs when a spark plug becomes loose or is ejected from its cylinder head due to wear, improper installation, or damaged threads. While it may seem daunting, fixing a spark plug blow out is manageable with the right tools and approach, allowing you to restore your engine’s functionality and prevent further damage.
Dealing with a spark plug blow out? Our expert guide shows you how to fix a spark plug blow out, step-by-step instructions for repairing damaged cylinder head threads.
What is a Spark Plug Blow Out?
Hearing a sudden, loud popping sound from your engine, followed by a loss of power and a rough idle, can be an alarming experience. This is often the classic sign of a spark plug blow out, a serious issue where the spark plug is forcibly ejected from the cylinder head. This happens when the threads in the cylinder head that hold the spark plug become stripped or damaged, failing under the immense pressure of engine combustion. While it sounds catastrophic, it is often a repairable problem. This guide will provide clear, step-by-step instructions on how to fix a spark plug blow out, empowering you to tackle this advanced but manageable repair and get your vehicle running smoothly again.
Guide on How to Fix a Spark Plug Blow Out
Step 1: Confirm the Spark Plug Blow Out
The first and most critical step is to confirm that a spark plug has indeed blown out. The symptoms are hard to miss: a sudden, loud pop, a dramatic loss of engine power, and a very rough, shaking idle. Visually inspect the engine bay. You will likely see the ignition coil and spark plug boot pushed up from its position on the cylinder head. The spark plug may be completely ejected or hanging loosely by the ignition coil wire. Identifying the correct cylinder is essential before proceeding with any repairs. This initial diagnosis confirms the problem and sets the stage for the repair process.
Step 2: Gather the Necessary Tools and Materials
This repair requires a specific set of tools, most importantly a spark plug thread repair kit, also known as a helicoil or time-sert kit. Ensure the kit matches your engine’s spark plug thread size. You will also need a socket set with a spark plug socket, torque wrench, compressed air source, and safety glasses. It is also wise to have a new spark plug and ignition coil on hand, as the old ones are often damaged during the blow out. Having all your tools and parts ready before you begin will make the process much smoother and prevent interruptions.
Step 3: Remove the Damaged Spark Plug and Ignition Coil
Before you can begin the repair, you must safely remove the remnants of the blown-out spark plug and the ignition coil. Carefully disconnect the electrical connector from the ignition coil. Then, unbolt and lift the coil off the cylinder head. If the spark plug is still loosely in the hole, use your spark plug socket to carefully unscrew and remove it. Inspect both the plug and the coil for any damage. The porcelain on the plug is often cracked, and the boot on the coil can be torn. These components will almost certainly need to be replaced.
Step 4: Prepare the Cylinder for Repair
With the spark plug hole exposed, you must ensure the piston in that cylinder is at the bottom of its stroke (Bottom Dead Center). This provides maximum clearance and helps prevent damage to the piston during the re-threading process. You can do this by manually turning the engine over using a socket on the crankshaft bolt. Additionally, it is a good idea to apply a thick layer of grease to the reaming tap you will use in the next step. This grease will catch most of the metal shavings, preventing them from falling into the cylinder.
Step 5: Re-Tap the Threads
This is the core of the repair. Using the tap provided in your thread repair kit, you will cut new, larger threads into the damaged spark plug hole. Attach the tap to a socket wrench and carefully begin threading it into the hole by hand. It is crucial to keep the tap perfectly straight to ensure the new insert and spark plug will seal correctly. Go slowly, turning the tap a quarter-turn at a time and then backing it out slightly to clear the metal shavings. Continue this process until the tap has cut threads all the way through the cylinder head.
Step 6: Clean the Cylinder of Debris
After you have finished tapping the new threads, you must remove any metal shavings that may have fallen into the cylinder, despite your best efforts with the grease. Use a source of compressed air with a long nozzle to blow out the spark plug hole and the cylinder thoroughly. A shop vacuum with a narrow attachment can also be used to suck out any remaining debris. This step is non-negotiable; leaving metal shavings inside the cylinder can cause catastrophic engine damage once the engine is started. Take your time to ensure it is perfectly clean.
Step 7: Install the Thread Insert
Now it is time to install the new threaded insert that will hold your spark plug. This insert is the key component of the repair kit. Apply a high-temperature thread-locking compound to the external threads of the insert. Then, using the installation tool provided in the kit, carefully screw the new insert into the newly tapped hole in the cylinder head. Thread it in until it is flush with or slightly below the surface of the cylinder head. The thread-locking compound will secure it permanently in place once it cures.
Step 8: Install the New Spark Plug and Coil
Once the thread insert is installed and the locking compound has had time to set (check the product instructions), you can install the new spark plug. Thread it into the new insert by hand to avoid cross-threading. Then, use a torque wrench to tighten it to the manufacturer’s specified torque setting. Over-tightening can damage the new insert or the cylinder head. After the plug is secure, install the new ignition coil, bolt it down, and reconnect the electrical connector. The repair is now mechanically complete.
Frequently Asked Questions (FAQ)
What Causes a Spark Plug Blow Out?
A spark plug blow out is almost always caused by improperly installed spark plugs. The primary reasons include:
- Under-tightening: If a spark plug is too loose, it can vibrate and slowly wear away the aluminum threads in the cylinder head until they fail.
- Over-tightening: This can stretch and weaken the threads, leading to failure under pressure.
- Cross-threading: Forcing a spark plug in at an angle can destroy the threads from the start.
Can I Drive My Car After a Spark Plug Blow Out?
It is strongly advised not to drive the vehicle after a spark plug blow out. The affected cylinder is no longer firing, which means you will have a severe loss of power and a very rough engine. Continuing to drive can cause unburned fuel to damage the catalytic converter and potentially lead to further engine damage. It is safest to have the vehicle towed to a location where it can be repaired.
Is a Thread Repair Kit a Permanent Fix?
Yes, when installed correctly, a high-quality thread repair insert (like a Time-Sert or Helicoil) is considered a permanent and reliable solution. These inserts are typically made of steel, which is much stronger than the original aluminum threads in the cylinder head. This makes the repaired threads more durable and less likely to fail in the future compared to the original factory threads.
How Much Does It Cost to Fix a Spark Plug Blow Out?
The cost can vary significantly. If you perform the repair yourself, your main expense will be the thread repair kit, which can range from $50 to over $200, plus the cost of a new spark plug and ignition coil. If you take it to a mechanic, the labor costs will be much higher. A professional repair can cost anywhere from $300 to $700 or more, depending on the vehicle and local labor rates.
Can Any Spark Plug Hole Be Repaired?
In most cases, yes. However, if the damage to the cylinder head is exceptionally severe or if a previous, poorly done repair has failed, it may not be possible to use a standard thread repair kit. In these rare instances, the only solution might be to remove the cylinder head and have it repaired by a specialized machine shop, or in the worst-case scenario, replace the cylinder head entirely, which is a much more expensive and labor-intensive job.
Conclusion
A spark plug blow out can seem like a disastrous engine failure, but it is a problem with a clear solution. With the right tools and a careful, methodical approach, repairing stripped spark plug threads is a task that a knowledgeable DIY mechanic can accomplish. The key is to work slowly, keep everything clean, and follow the instructions provided with your thread repair kit. By understanding the process and taking on the challenge, you not only save a significant amount of money but also gain invaluable mechanical experience. Now that you know how to fix a spark plug blow out, you are better prepared to handle one of the more intimidating-sounding engine repairs.