The 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, leaner air to fuel operation, a higher compression ratio, and retardation of the timing. Higher voltage reduces the service life of components such as spark plugs, wires, and transformers.
The service life of the spark plug is different for different applications. The expected service life of the spark plug is approximately 3000 service hours. This service life if for an engine that is running on pipeline natural gas at standard performance sheet settings and conditions. To help predict the spark plug service life, use Cat Electronic Technician (ET) to monitor the "Cylinder #X Transformer Secondary Output Voltage Percentage" parameter. The value of this parameter will increase as the spark plug gap wears over time. Experience at the particular site will help to determine the proper interval for replacement of the spark plugs.
If a diagnostic code is generated for the ignition transformer secondary circuit, replacement of the spark plug may be necessary. Misfire and a cold cylinder are other indications of a worn spark plug. Use Cat ET to monitor the exhaust port temperatures in order to locate a cold cylinder.
Removing the Spark Plug
- Remove cover (1).
Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring. Do not attempt to remove the valve covers when the engine is operating. The transformers are grounded to the valve covers. Personal injury or death may result and the ignition system will be damaged if the valve covers are removed during engine operation. The engine will not operate without the valve covers. |
Illustration 1 | g00925913 |
(1) Cover (2) Wiring harness (3) Transformer (4) Seal (5) Spark plug (6) Valve cover |
- Remove wire harness (2) from transformer (3) .
- Remove the two remaining bolts that secure transformer (3). Remove transformer (3) from valve cover (6) .
- Inspect O-ring seal (4). If the seal is hard, cracked, or melted, install a new 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.
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.
- Use a 216-1685 deep well socket, an extension, and a breaker bar to loosen spark plug (5). After the spark plug has been loosened, use the socket and extension to remove the spark plug by hand. Problems with threads can be identified when removing by hand. After the spark plug has been removed, discard the used spark plug gasket.
If the spark plug resists removal by hand, apply penetrating oil to the threads. To help the oil penetrate the threads, turn the spark plug back and forth until the spark plug is loose.
If the spark plug could not be removed by hand, clean the threads with a Spark Plug Seat Cleaner. This tool scrapes debris from the seat and from the threads in the cylinder head. Be sure to clean any debris from the cylinder.
NOTICE |
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Do not use a thread tap. A thread tap will remove metal unnecessarily. The threads could be stripped and the cylinder head could be damaged. |
Inspecting the Spark Plug
Illustration 2 | g00935078 |
(7) Terminal post (8) Insulator (9) Shell (10) Gasket (11) Hole in the spark plug precombustion chamber |
Inspect the spark plug closely for damage. The condition of the spark plug can indicate the operating condition of the engine.
Terminal post (7) 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.
Insulator (8) is covered with Teflon. If the cover is cracked or loose, discard the spark plug.
Faint marks may extend from shell (9) onto the insulator. The marks may be a result of a corona that forms at the top of the shell. The conductor will develop a corona when a high voltage potential ionizes the air which is a normal condition. This condition is not an indication of leakage between the shell and the insulator.
Inspect shell (9) 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.
Inspect the spark plug precombustion chamber for deposits. Make sure that holes (11) in the spark plug precombustion chamber are not blocked.
A light brown deposit or a beige deposit 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 mixture
A spark plug can operate despite a buildup of ash. Large deposits may retain heat which can cause premature fuel ignition. Premature fuel ignition can lead to uncontrollable detonation.
Cleaning the Spark Plug
Do not use glass beads to clean the spark plug. The beads could enter the precombustion chamber through the holes. The beads could clog the holes in the spark plug precombustion chamber.
Use a brass wire brush to clean the spark plug. Be careful not to damage the Teflon cover.
Installing the Spark Plug
- Ensure that the spark plug is clean and free of dirt and oil.
Note: Do not use anti-seize compound on spark plugs. Most of the heat is transferred through the threads and the seat area of the spark plug. Contact of the metal surfaces must be maintained in order to provide the heat transfer that is required.
- Always use a new gasket when a spark plug is installed. If a used spark plug is installed, place a new gasket on the spark plug. Orient the tabs of the gasket toward the spark plug precombustion chamber. Otherwise, the gasket may not seat properly. If a gasket for a spark plug is installed incorrectly, do not increase the torque on the spark plug in order to improve the seal. Do not reuse the gasket. Install a new gasket.
- Install spark plug (5) by hand until the spark plug contacts the gasket. Torque the spark plug to the proper specification. Refer to Specifications, "Spark Plug" for the proper torque specification.
NOTICE |
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Do not overtighten the spark plug. The shell can be cracked and the gasket can be deformed. The metal can deform and the gasket can be damaged. The shell can be stretched. This will loosen the seal that is between the shell and the insulator, allowing combustion pressure to blow past the seal. Serious damage to the engine can occur. Use the proper torque. |
- Ensure that the transformer and the extension are clean and free from dirt and oil. Lubricate O-ring seal (4) with one of the following lubricants:
- Dielectric Grease
- Silicone Lubricant
- Dielectric Grease
- Install transformer (3). Orient the transformer toward wiring harness (2). Connect the wiring harness.
- Install cover (1) .