- Normal fuel consumption
- Normal levels of emissions
- Maximum service life of the spark plugs
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 and a higher compression ratio. Higher voltage reduces the service life of components such as spark plug wires and transformers.
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| Illustration 1 | g00294914 |
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(1) Connector
(2) Bolt (3) Transformer | |
- Ensure that the mode control switch is in the "STOP" or "OFF/RESET" position.
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NOTICE Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.
- Disconnect the wiring harness. Use pliers to turn connector (1) counterclockwise.
- Remove three bolts (2).
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Illustration 2 g00295199 (3) Transformer
(4) Gasket
(5) Extension
(6) Spark plug
(7) Gasket
(8) Cover
(9) TubeNote: Some engines that are certified by the Canadian Standards Association (CSA) do not have gasket (4).
- Remove transformer (3) and gasket (4). Inspect gasket (4). If the gasket is worn or damaged, discard the gasket and use a new gasket for assembly.
- Remove extension (5).
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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.
- Debris may have collected near the spark plug. 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
22.23 mm (.875 inch) 4C-4601 Spark Plug Socket and an extension to loosen spark plug (6). After the spark plug has been loosened, remove the spark plug by hand in order to detect problems with the threads. After the spark plug has been removed, discard used gasket (7).
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The use of a thread tap will remove metal unnecessarily. This will also reduce the heat transfer for the spark plug. This can result in a reduction of the spark plug service life and a reduction of the detonation margin. |
If the spark plug resists removal by hand, apply penetrating oil to the threads. Use the wrench and apply steady pressure to the spark plug until the spark plug is loose.
Note: Cover (8) and tube (9) must be removed in order to clean the threads.
If the spark plug cannot be removed by hand, clean the threads with 9U-7511 Spark Plug Seat Cleaner. This tool scrapes debris from the seat and from the threads.
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| Illustration 3 | g00295207 |
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(1) Terminal post
(2) Insulator (3) Shell (4) Gasket (5) Electrode | |
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, 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. Corona develops when a very high voltage potential ionizes the air that surrounds a conductor. This is a normal condition. This 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 loosen the shell. Discard any spark plug that has a shell that is cracked or loose.
Inspect electrode (5) for excessive wear. Flat surfaces with sharp edges provide the best conditions for creating a spark. An electrode will become worn from use. The surfaces erode. A higher voltage is required in order to produce a spark.
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| Illustration 4 | g00353860 |
| (6) Precious metal pads on the electrode and the ground strap | |
Caterpillar spark plugs have precious metal pads (6) on the tips of the electrode and the ground strap. This material will gradually erode.
Replace the spark plug if the precious metal is worn off.
A light brown or beige deposit around the electrode is produced by normal operation. White deposits or gray deposits 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
A spark plug can operate despite a buildup of ash. However, a buildup of ash can cover the electrode gap. This will cause misfire. Large deposits may retain heat which can cause premature fuel ignition. This can lead to uncontrollable detonation.
A standard ohmmeter (nine volt) can be used for measuring the resistance of the spark plug. The ohmmeter can be used only for spark plugs with wire-wound resistors. It is not possible to use a standard ohmmeter (nine volt) for measuring the resistance of other types of spark plugs. Measure the resistance between terminal post (1) and electrode (5). Discard any spark plug with a wire-wound resistor if the resistance is outside the range of 1k to 1.5k Ohms.
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.
- Use care in order to clean only the electrode and the insulator near the electrode.
- Do not use glass beads on the outside of the shell or on the upper part of the insulator.
- Before installing the spark plug, set the electrode gap to
0.29 ± 0.03 mm (.011 ± 0.001 inch) .Adjust the electrode gap by bending the ground electrode at the existing bend. Then bend the strap near the weld in order to achieve proper alignment and even spacing between the two precious metal surfaces. Measure the electrode gap after the alignment. Correct the electrode gap, if necessary.
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. The surfaces must be in contact in order to provide the heat transfer that is required.
- Ensure that the spark plug is clean and free of dirt and oil.
- Always use a new gasket when a spark plug is installed. If a used spark plug is installed, place a new 9Y-6792 Gasket on the spark plug. Orient the tabs of the gasket toward the electrode. 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.
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NOTICE Do not overtighten the spark plugs. The shell can be cracked and the gasket can be deformed. 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.
- Install the spark plug by hand until the spark plug bottoms out. Tighten the spark plug to
68 ± 4 N·m (50 ± 3 lb ft) . - Ensure that the connection points of the extension are clean.
- Use a mild abrasive cleaner to clean deposits and/or corrosion from the extension at connection points (1) and (2).
- Apply one of the following lubricants to the extension at connection points (1) and (2):
This will help to protect the connection points of the extension from corrosion.
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Illustration 5 g00451015 (1) Connection of the extension and the transformer
(2) Connection of the extension and the spark plug - Ensure that the internal spring exerts force on the connection points. Install the extension onto the spark plug.
- Ensure that the transformer assembly is clean and free of dirt and oil. Center the extension into the transformer. Install the transformer.
- Connect the wiring harness. Tighten the connector clockwise with pliers until the connector cannot be loosened by hand.
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 falsely measure the actual electrode gap due to curvature of the used precious metal surfaces.
