90406-ZY3-000 Honda WASHER, PLAIN (8MM) (Honda Code 6994198).

Maintenance of the spark plugs is required to achieve the following benefits:
Normal fuel consumption
Normal level of emissions
Maximum service life of the spark plugsThe service life of the spark plugs is affected by fouling due to deposits from the oil and by peak voltage. Maintenance of the ignition system is also affected by voltage. Higher voltage is required by higher inlet manifold air pressure and a higher compression ratio. Higher voltage reduces the service life of components such as spark plugs, wires, and transformers.Removing the Spark Plug
Illustration 1 g06254717
(1) Valve cover
(2) Bolt and washer
(3) Seal
Remove bolts (2). Remove valve cover (1). Inspect seal (3). If the seal appears to be worn or damaged, install a new seal.
Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.
Illustration 2 g06254410
(1) Wiring harness connection
(2) Transformer
(3) Extension
(4) Spark plug
Disconnect wiring harness from transformer (2). Pull transformer and extension straight away from the cylinder head.
Inspect lip seal . If the seal is worn or damaged, discard the seal and use a new seal for assembly.
Illustration 3 g00787371
(8) O-ring seal
Inspect O-ring seal (8). If the seal is hard, cracked, or melted, install a new seal.
Pressurized air can cause personal injury. When pressurized air is used for cleaning, wear a protective face shield, protective clothing, and protective shoes.
Note: Excessive buildup of oil in the spark plug well is an indication of a damaged lip seal on the transformer. If this condition is found, clean the surface of the seal groove. Replace seal.
Debris may have collected in the spark plug well. Thoroughly remove any debris. Use compressed air. The maximum air pressure for cleaning purposes must be below 207 kPa (30 psi). Ensure that the area around the spark plug is clean and free of dirt and debris.
Use a 177.8 mm (7/8 inch), 4C-4601 Spark Plug Socket, an extension, and a breaker bar to loosen spark plug (7). After the spark plug has been loosened, use the socket and extension to remove the spark plug by hand to detect problems with the threads. After the spark plug has been removed, discard the used spark plug gasket.Inspecting the Spark Plug
Inspect the spark plug closely for damage. The condition of the spark plug can indicate the operating condition of the engine.
Illustration 4 g00838300
(1) Terminal post
(2) Insulator
(3) Shell
(4) Gasket
(5) ElectrodeTerminal post (1) must not move. If the terminal post can be moved by hand, carefully tighten the post into the threads of the insulator. If the post cannot be tightened, discard the spark plug.Inspect insulator (2) for cracks. If a crack is found, discard the spark plug.Faint marks may extend from shell (3) onto the insulator. The marks may be a result of corona that forms at the top of the shell. The conductor will develop a corona when a high-voltage potential ionizes the air. This corona is a normal condition. This corona is not an indication of leakage between the shell and the insulator.Inspect shell (3) for damage. Cracks can be caused by overtightening the spark plug. Overtightening can also yield the metal which loosens the shell. Discard any spark plug that has a shell that is cracked or loose.
Illustration 5 g00787372
(6) Precious metal tips on the electrode and the ground strapCat spark plugs have precious metal tips (6) on the electrode and the ground strap. This material will gradually erode. Use extreme care when you set the electrode gap. Maintain even spacing and proper alignment between the two precious metal surfaces.Replace the spark plug if the precious metal is worn off.A light brown deposit or a beige deposit around the electrode is produced by normal operation.Deposits that are gray or black may be caused by the following substances:
Excessive oil
Use of the wrong oil
A substance that is introduced through the fuel system or the air system
Poor combustion because of a rich air/fuel mixtureA spark plug can operate despite a buildup of ash. However, a buildup of ash can cover the electrode gap. This condition may cause a misfire. Large deposits may retain heat which can cause premature fuel ignition. This condition can lead to uncontrollable detonation.Cleaning the Spark Plug
Thoroughly clean the spark plug. Do not use a wire brush. Glass beads are the preferred method for cleaning.Follow these guidelines for using glass beads:
Always use clean glass beads.
Only use glass beads on the electrode and the insulator near the electrode.
Do not use glass beads on any other area of the spark plug.
Clean the rest of the spark plug with nonflammable solvent.Installing the Spark Plug
Note: Use the 9U-7516 Spark Plug Gauge to measure the electrode gap. Do not use a flat feeler gauge for measuring the electrode gap of used spark plugs. A feeler gauge will incorrectly measure the actual electrode gap because the used precious metal tips are curved.
Before installing the spark plug, set the electrode gap according to the engine Specifications manual.Adjust the electrode gap, if necessary.