As you prepare to re-condition your spark plugs, keep the following in mind before you start. Always follow the manufacturer's instructions. Always wear appropriate safety equipment. Never use carbon tetra chloride to clean spark plugs. Never soak spark plugs. And before cleaning inspect your spark plug for obvious reasons to reject it. Write down anything relating to engine operating issues like excessive carbon, lead, oil, residues, or any other anomalies for later use. Begin cleaning by removing lead build up and firing end of the spark plug using a small pick or vibratory cleaning tool. After removing deposits from firing end of the plug, if you have one available, use a grip blasting tool to clean out any remaining residue in the firing end. Be sure to use only the manufacturer's approved blast media on spark plugs. Anything other than an approved media may damage the spark plug, reducing its operating life, especially glass bead media. Clean off the threads of the firing end of the spark plug with stuttered solvent or mineral spirits using a stiff non-metallic bristle brush. After using solvent, completely dry off the spark plug with compressed air. With the firing end of the plug cleaned and dried, carefully inspect the firing end with a 10-time magnifying glass for any cracks, chips, or thread damage. Minor thread damage may be dressed or repaired. Be sure to make note of plugs with damaged threads. Thurally inspect the holes for the plugs before reinstalling them. Clean the outside of the rest of the spark plug with a clean cloth and stuttered solvent to remove any grease or residue. Clean the inside of the terminal well with a cotton swab and stuttered solvent. Be sure to thoroughly dry the terminal well with compressed air. Inspect the terminal end of the spark plug for any damage. Check the spark plug resistance with an ohm meter. The spark plug should show between 500 ohms and 3000 ohms resistance. If the resistance is 5000 ohms or greater, replace the spark plug. Take the clean and tested spark plug and check the gap. Adjust the gap as needed. Spark plugs for aircraft will have a service manual that will give you specific information about your spark plugs. Be sure to get a copy of the service manual from the manufacturer. Always have approved data on hand and read it thoroughly before servicing any aircraft part or assembly.