Note: Condensation can form in spark plugs that have precombustion chambers. This condensation can cause difficulty for cold start-ups. To avoid condensation, maintain the coolant in the cylinder block at a minimum temperature of 43 °C (110 °F) continuously.
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, a higher compression ratio, or 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 service life of the spark plug is approximately 3000 service hours. The spark plug may be good for a considerable period beyond 3000 service hours. To help predict the service life of the spark plug, 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 secondary circuit of the transformer, the spark plug is to be replaced. 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 bolts (1). Remove valve cover (2). Inspect O-ring seal (3). If the seal appears to be worn or damaged, discard the seal and use a new seal for assembly.
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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. |
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| Illustration 1 | g00760567 |
(1) Bolt (2) Valve cover (3) O-ring seal | |
- Disconnect wiring harness (4) from transformer (5). Be careful to depress the retainer clip away from the connector. Remove transformer (5) .
| NOTICE |
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Pulling on the wiring harness may break the wires. Do not pull on the wiring harness. |
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| Illustration 2 | g00760565 |
(4) Wiring harness (5) Transformer (6) Lip seal (7) Spark plug | |
- Inspect lip seal (6). If the seal is worn or damaged, discard the seal and install a new seal.
- Inspect O-ring seal (8). If the seal is hard, cracked, or melted, install a new seal.
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| Illustration 3 | g00760568 |
(8) O-ring 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.
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Pressurized air can cause personal injury. When pressurized air is used for cleaning, wear a protective face shield, protective clothing, and protective shoes. |
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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 (6) .
- Use a 20.638 mm (13/16 inch) deep well 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. Removing the spark plug by hand will enable you to detect problems with the threads. 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 the 9U-7511 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.
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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
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| Illustration 4 | g00838122 |
(1) Terminal post (2) Insulator (3) Shell (4) Gasket (5) Hole in the precombustion chamber of the spark plug | |
Inspect the spark plug closely for damage. The condition of the spark plug can indicate the operating condition of the engine.
Terminal 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.
Insulator (2) is covered with Teflon. If the cover is cracked or loose, discard the spark plug.
Faint marks may extend from shell (3) 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. This corona is a normal condition. This condition 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.
Inspect the precombustion chamber of the spark plug for deposits. Make sure that holes (5) in the precombustion chamber of the spark plug 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. This condition 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 precombustion chamber of the spark plug.
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 9Y-6792 Spark Plug Gasket on the spark plug. Orient the tabs of the gasket toward the precombustion chamber spark plug. 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 the spark plug by hand until the spark plug contacts the gasket. Tighten the spark plug according to the engine Specifications manual.
| 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 (8) (Illustration 3) with one of the following lubricants:
- Install the transformer. Orient the transformer toward the wiring harness. Carefully align the socket of the transformer with the wiring harness connector. Connect the wiring harness.
Note: If the locking tab of the connector or the connector of the transformer are damaged, install a 178-0565 Retainer .
- Install the valve cover.
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| Illustration 5 | g00838130 |
178-0565 Retainer on the connector ot the transformer for the wiring harness | |