Spark plug replacement
1. The spark plugs are threaded into the sides of the cylinder heads, adjacent to the exhaust ports.
2. In most cases, the tools necessary for spark plug replacement include a spark plug socket, which fits onto a ratchet (spark plug sockets are padded inside to prevent damage to the porcelain insulators on the new plugs), various extensions and a gap gauge to check and adjust the gaps on the new plugs (see illustration). A special plug wire removal tool is available for separating the wire boots from the spark plugs, but it isn’t absolutely necessary. A torque wrench should be used to tighten the new plugs.
25.2 Tools required for changing the spark plugs
1 Spark plug socket — This will have special padding inside to protect the spark plugs porcelain insulator
2 Torque wrench — Although not mandatory, using this tool is the best way to ensure the plugs are tightened properly
3 Ratchet — Standard hand tool to fit the spark plug socket
4 Extension — Depending on model and accessories, you may need special extensions and universal joints to reach one or more of the plugs
5 Spark plug gap gauge — This gauge for checking the gap comes in a variety of styles. Make sure the gap for your engine is included
3. The best approach when replacing the spark plugs is to purchase the new ones in advance, adjust them to the proper gap and replace them one at a time. When buying the new spark plugs, be sure to obtain the correct plug type for your particular engine. This information can be found in the factory owner’s manual and this Chapter’s Specifications.
4. Allow the engine to cool completely before attempting to remove any of the plugs. While you’re waiting for the engine to cool, check the new plugs for defects and adjust the gaps.
5. The gap is checked by inserting the proper-thickness gauge between the electrodes at the tip of the plug (see illustration). The gap between the electrodes should be as listed in this Chapter’s Specifications. The gauge should just slide between the electrodes with a slight amount of drag.
25.5 When checking the spark plug gap, the wire should slide between the electrodes with a slight drag
6. Remove the spark plug wire from one spark plug. Pull only on the rubber boot on the end of the wire — do not pull on the wire. A plug wire removal tool should be used, if available (see illustration).
25.6 A tool like this one makes the job of removing the spark plug boot easier twist it back-and-forth and pull only on the boot
7. If compressed air is available, use it to blow any dirt or foreign material away from the spark plug hole. This will eliminate the possibility of debris falling into the cylinder as the spark plug is removed.
8. Place the spark plug socket over the plug and remove it from the engine by turning it in a counterclockwise direction (see illustration).
25.8 Use a socket and extension to unscrew the spark plugs — various length extensions and perhaps a flex-joint may be
required to reach some plugs
9. Compare the spark plug to those shown in the photos located on the inside back cover of this book to get an indication of the general running condition of the engine.
10. Before installing the new plugs, it is a good idea to apply a thin coat of anti-seize compound to the threads (see illustration).
25.10 Apply a thin coat of anti-seize compound to the spark plug threads, being careful not to get any near the lower threads
11. Thread one of the new plugs into the hole until you can no longer turn it with your fingers, then tighten it with a torque wrench (if available) or the ratchet. Where plugs are at the rear of the engine and harder to reach, it might be a good idea to slip a short length of rubber hose over the end of the plug to use as a tool to thread it into place (see illustration). The hose will grip the plug well enough to turn it, but will start to slip if the plug begins to cross-thread in the hole — this will prevent damaged threads and the accompanying repair costs.
25.11 A length of snug-fitting rubber hose will save time and prevent damaged threads when installing the spark plugs
12. Attach the plug wire to the new spark plug, again using a twisting motion on the boot until it’s seated on the spark plug.
13. Repeat the procedure for the remaining spark plugs, replacing them one at a time to prevent mixing up the spark plug wires.