Spark Plugs and Wires

How do you change spark plugs?


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Wiki User
2015-07-15 18:19:18
2015-07-15 18:19:18

First, get a correct size spark plug socket, the kind with the rubber insert. Make sure it is the correct size for your car's plugs. Older cars used 13/16" (REAL old cars had even larger sizes); most modern cars use 5/8". Allow the engine to cool so that you will not burn your knuckles, especially on the exhaust manifold. On some engines universal joints for the socket drive extension bar is useful. Spark plug sockets with built-in universal joints are also available. Several lengths of extension bars may come in handy: 3", 6", etc. They can be used in combination for really long reaches. A compressed air blow gun (wear safety goggles!!) with a long nozzle should be used to blow all grit and trash from the spark plug wells or recesses. You don't want any grit or trash to get into the cylinder or to foul the spark plug threads. If there is built-up crud around the plugs, use a good engine cleaner like "Gunk" after the engine has cooled to where you can touch it comfortably. After it has a chance to soak, spray with a water jet, then blow dry with the blow gun. If you can reach the spark plug boots (the rubber sleeves or elbows at the end of the spark plug cables), twist them back and forth just a little to break them free from the spark plug insulators. You don't care about damaging the spark plugs but if you aren't replacing the spark plug cables ("wires") you don't want to pull the cables out of the connectors that snap onto the spark plug terminals. There are a number of hook tools and pliers made to pull the cables loose from the spark plugs. Don't pull on the cables - they likely will pull out of the terminals or may break the "wire" (actually a fiberglass string filled with graphite on most street applications) inside the cable insulator. Take the cables loose and replace the spark plugs one at a time so that the order of the cables is not changed. Unscrew the spark plug and set it aside in order for inspection. Make sure the spark plug threads and seat in the engine cylinder head are clean and grit free. Make sure the threads on the spark plug are clen and undamaged. If the thread is dinged, exchange it for another new plug. Apply a small amount of anti-seize compound (NEVER use oil or grease!) on the spark plug threads. If you can reach it with your hand, screw the spark plug into the hole with your fingers. If there is any resistance, back off and inspect for whatever is jamming it. If you have to, use a spark plug holder (not the socket) to insert and screw in the plug finger tight. Now use the socket to tighten the plug to specification. Old-fashioned flat seat plugs, the ones with gasket washers, are tightened about one turn from finger tight. Modern tapered seat plugs are tightened about 1/16 turn from finger tight. Use of a torque wrench is strongly recommended. Spark plugs are NOT 12mm or 14mm screws.


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