How to Clean a Spark plug

So you can't get your snowmobile or lawn mower or chainsaw to start, what can you do? Well, gasoline engines need an ignition spark to run. If the spark plug is fouled, the engine won't start. Here is how to clean the plug.

Difficulty: Moderately Easy

Instructions

1. First, find the spark plug, then remove it, inspect it, clean it, and finally, reinstall it. The plug must receive high voltage electricity, so look for a large, flexible, black wire going to the top of the engine. The wire will have a cap or a clip that protects the top of the spark plug. Pull the cap or plug off the top of the plug. Don't pull on the wire itself. It might come out, and then it would need to be repaired. You can identify the spark plug by the white ceramic insulator on its top.

2. Removing the plug will usually require a 13/16 inch deep socket wrench. Turn the plug counter-clockwise to remove it. Many small machines like chainsaws and snowmobiles provide a tool kit with the correct socket for the spark plug. Be careful not to crack or break the ceramic portion of the spark plug. If you do, it must be replaced. If the engine has more than one spark plug, make sure you do not mix up the spark plug wires. They must be put back in the same order when you reinstall the cleaned spark plugs.

3. Inspect the threaded end of the plug. There is an electrode down through the center of the ceramic insulator that carries the electricity into the cylinder. There is an electrode attached to the side of the threaded portion that extends nearly to the center electrode. The electric spark jumps from the center electrode to the grounded electrode to ignite the fuel/air mixture in the cylinder. If the plug is working correctly it will be dry and brown or black in color around the center electrode. If it is black and oily, it hasn't been firing. If it is dry and very sooty it still may be shorting out. The gap between the center and ground electrodes must not be bridged with carbon.

4. Cleaning the spark plug requires drying it out and removing any carbon or soot that might create an alternate path for the electric spark. Clean the ceramic insulator by wiping with a soft cloth. Clean any oily dirt off the threaded portion by wiping or brushing with a wire brush if necessary. The most difficult part is digging and scraping the oily soot and carbon out of the cavity inside the threaded end. There are cleaning tools made for this purpose available at any automotive supply store. Or you can use any small slender tool that will fit down into the cavity. You can even make a suitable tool by hammering a small nail to a suitable miniature blade shape. Scrape and clean back and forth in the cavity from one side of the ground electrode around to the other side and tap and blow the carbon residue out. Be careful not to mash the ground electrode down onto the center post if you tap the plug to remove soot and debris. If that happens, the plug must be re-gapped to its original spacing. Use your tool to wipe the inside of the cavity with a piece of clean cloth like that from an old Tee shirt. When the spark plug is clean and dry, put it back in the engine and reattach the plug wire.

5. When reinstalling the spark plug, make sure no dirt or debris falls into the engine cylinder. The spark plug has a small compression washer on the threaded end that seals the plug in the cylinder. Do not over tighten the plug. You might strip the threads or break the plug. As a general rule, put it back about as tightly as when it was removed. A mechanic would use a torque wrench when installing new spark plugs to factory specification.

Tips & Warnings

• A cleaned plug can be reattached to the spark plug wire and placed where it will make a solid ground with the metal of the engine. When the engine is cranked, you will be able to hear and observe a small blue spark across the electrodes. That will confirm that the plug is able to deliver an ignition spark in the engine cylinder
• You can confirm that electricity is getting to the spark plug by touching the top while the engine is being cranked but that is painful and dangerous--like grabbing an electric fence.

[parollins]

on 3/16/2009 Wow! You are very detailed and you can't go wrong. 5* and a recommend.