London Vehicle Engine Maintenance - How to Change Your Spark Plugs
The spark plug is the final step in the ignition circuit. It takes the voltage surge from the distributor and creates a high-voltage spark that ignites the compressed air/fuel mixture in each cylinder. In a well-tuned engine this produces the power which turns the crankshaft, creating power to move the car forward. Regular spark plug replacement is one of the easiest ways to optimize performance and fuel economy.
Here are the steps to replace each spark plug in your car's engine (Tip: The plugs are usually easier to remove when the engine is warm):
- First check and gap the new spark plugs against manufacturers' specifications. Use a wire type gauge, which is quite accurate, when gapping spark plugs. The wire gauge should slide between the electrodes with a slight drag. There's a tool designed for changing the gap, which slightly bends the electrode. When replacing spark plugs, removing the old plugs and replace one at a time, to avoid crossing a spark plug wire.
- Pull the boot off the plug by gently twisting and pulling. Don't pull the plug wire away from the boot.
- Brush dirt away from the spark plug area, so it won't fall into the cylinder chamber.
- Remove the spark plug using the correct size spark plug socket (usually 13/16 or 5/8 inch), turning counterclockwise, applying slight pressure on the socket. This will prevent the socket from stripping on the plug.
- When the plug is removed, compare it to the new plug. Be sure that the reach (threaded area) is the same and the plug has the same overall appearance. While spark plugs are basically the same, some differences can cause engine damage. Record different part number equivalents for various brands appropriate for your car, to aid in future purchases. See KEEPING A LOG BOOK
- To install the new plug, placing it into the spark plug socket and --by hand-- screw the plug clockwise into the engine. A drop of penetrating oil on the spark plug threads will help avoid cross-threading. Don't use undue force, which may strip the plug threads. Once threaded, you can use the socket to ratchet the plug until snug. Don't over-tighten.
- Reinstall the spark plug wire. Look for any cracks or other signs of wear. Be sure the plug wire is seated, and snaps into the plug terminal.
- Follow the above procedure to complete all spark plugs. Do one at a time to prevent wire mix-up.