See Figures 1 through 4
The spark plugs should be replaced every 30,000 miles (48,300 km).
Spark plugs ignite the air and fuel mixture in the cylinder as the piston reaches the top of the compression stroke. The controlled explosion that results forces the piston down, turning the crankshaft and the rest of the drive train.
The average life of a spark plug is dependent on a number of factors: the mechanical condition of the engine, the type of fuel, the driving conditions and the driver. Although the standard factory plugs will last a considerable period of time, extended life may be gained in some engines by using platinum-tipped plugs. You must decide if the benefits outweigh the extra cost.
When you remove the spark plugs, check their condition. They are a good indicator of the condition of the engine. A small deposit of light tan or gray material (or rusty red with some fuels) on a spark plug that has been used for any period of time is to be considered normal. Any other color, or abnormal amounts of deposit, indicates that there is something amiss in the engine.
The gap between the center electrode and the side or ground electrode can be expected to increase very slightly under normal conditions.
When a spark plug is functioning normally or, more accurately, when the plug is installed in an engine that is functioning properly, the plugs can be taken out, cleaned, re-gapped, and reinstalled in the engine without doing the engine any harm. This is acceptable as an improvement or emergency measure, but new plugs are always recommended.
When, and if, a plug fouls and begins to misfire, you will have to investigate, correct the cause of the fouling, and either clean or replace the plug. Replacement is always recommended if possible.
Spark plugs suitable for use in your engine are offered in different heat ranges. The amount of heat which the plug absorbs is determined by the length of the lower insulator. The longer the insulator the hotter the plug will operate; the shorter the insulator, the cooler it will operate. A spark plug that absorbs little heat and remains too cool will accumulate deposits of lead, oil, and carbon, because it is not hot enough to burn them off. This leads to fouling and consequent misfiring.
A spark plug that absorbs too much heat will have no deposits, but the electrodes will burn away quickly and, in some cases, preignition may result. Preignition occurs when the spark plug tips get so hot that they ignite the air/fuel mixture before the actual spark fires. This premature ignition will usually cause a pinging sound under conditions of low speed and heavy load. In severe cases, the heat may become high enough to start the air/fuel mixture burning throughout the combustion chamber rather than just to the front of the plug. In this case, the resultant explosion will be strong enough to damage pistons, rings, and valves.
In most cases the factory recommended heat range is correct; it is chosen to perform well under a wide range of operating conditions. However, if most of your driving is long distance, high speed travel, you may want to install a spark plug one step colder than standard. If most of your driving is of the short trip variety, when the engine may not always reach operating temperature, a hotter plug may help burn off the deposits normally accumulated under those conditions.
REMOVAL & INSTALLATION
- Place a piece of masking tape around each spark plug wire and number it according to its corresponding cylinder.
- Pull the wires from the spark plugs, grasping the wire by the end of the rubber boot and twisting off.
Avoid spark plug removal while the engine is hot. Since the cylinder head spark plug threads are aluminum, the spark plug becomes tight due to the different coefficients of heat expansion. If a plug is too tight to be removed even while the engine is cold, apply a solvent around the plug followed with an application of oil once the solvent has penetrated the threads. Do this only when the engine is cold.
- Loosen each spark plug with a spark plug socket. When the plug has been loosened a few turns, stop to clean any material from around the spark plug holes; compressed air is preferred. If air is not available, simply use a rag to clean the area.
- Remove and inspect the spark plugs; if necessary, clean them.
- Check the gap of the plugs with a feeler gauge. Apply an anti-seize compound to the spark plug threads and hand tighten them into the cylinder head. Torque the spark plugs into the cylinder head to 13 ft. lbs. (18 Nm).
- Connect the wires to the plugs, in the correct order, making sure that each is securely fitted.
INSPECTION & CLEANING
See Figures 5 through 9
Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. This may be done with very fine sandpaper or a small flat file. Do not use a wire brush. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50 percent.
Check the spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified-size wire gauge must fit in the gap with slight resistance.
NEVER adjust the gap on a platinum-tipped spark plug.
Always check the gap on new plugs too. NEVER rely on so-called "pre-gapped" plugs. Do not use a flat feeler gauge when measuring the gap; the reading will be inaccurate. Wire-type plug gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely never bend the center electrode. Also, be careful not to bend the side electrode too far or too often. It may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.