G3406 Engine Caterpillar


Spark Plugs - Inspect/Adjust/Replace

Usage:

G3406 1RK

------ WARNING! ------

Ignition systems can cause electrical shocks. Avoid contacting the ignition system components and wiring during operation.


Maintenance of the spark plugs is required in order to achieve the following benefits:

  • Normal fuel consumption

  • Normal level of emissions

  • Maximum service life of the spark plugs

  • Stable operation

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, and a leaner air/fuel ratio. Higher voltage reduces the service life of components such as spark plugs, wires, and transformers.

Removing the Spark Plug

Standard Ignition System

  1. Turn the ignition switch to the "OFF" position to ground the magneto and discharge any capacitors that may be charged.


    Illustration 1g02657458
    (1) Seal
    (2) Wire
    (3) Transformer assembly
    (4) Spark plug
    (5) Boot


    NOTICE

    Pulling on the wiring harness may break the wires. Do not pull on the wiring harness.


  2. Disconnect the wire from the transformer. The wire may break if you pull on the wire.

  3. Remove the boot and remove the extension.

    ------ WARNING! ------

    Pressurized air can cause personal injury. When pressurized air is used for cleaning, wear a protective face shield, protective clothing, and protective shoes.


  4. Ensure that the area around the spark plug is clean and free of dirt and debris. Thoroughly remove any debris. Use compressed air. The maximum air pressure for cleaning purposes must be below 207 kPa (30 psi). The spark plug can also be cleaned with a nonmetallic brush.

  5. Use a spark plug socket with an extension in order to remove spark plug.


NOTICE

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.

If it is difficult to remove the spark plug by hand, clean the internal threads with the 154-9521 Spark Plug Seat Cleaner. This tool scrapes debris from the seat and from the threads in the spark plug adapter. Be sure to remove any debris from the cylinder.

CSA Ignition System

    Note: The CSA ignition system is equipped with an integral transformer. The transformer screws onto the spark plug. The transformer and the spark plug are removed separately. The transformer and the spark plug are installed separately. Do not overtighten the transformers.



    Illustration 2g02657478
    CSA Ignition System
    (6) Wiring harness
    (7) Boot
    (8) Transformer
    (9) Copper washer
    (10) Spark plug
    (11) Spark plug gasket

  1. Turn the ignition switch to the OFF position.

  2. Disconnect the wiring harness.

  3. Remove the boot.

  4. Remove the transformer.

  5. Ensure that the area around the spark plug is clean. Ensure that the area around the spark plug is free from dirt and debris. Remove spark plug and remove gasket from the cylinder head. Remove the gasket and remove copper washer . Discard the gasket and discard the copper washer.

Inspecting the Spark Plug



Illustration 3g02657482
(12) Terminal post
(13) Insulator
(14) Shell
(15) Gasket
(16) Electrodes

Inspect the spark plug closely for damage. The condition of the spark plug can indicate the operating condition of the engine.

The terminal post must not move. If the terminal post can be moved by hand, discard the spark plug.

Inspect the insulator for cracks. If a crack is found, discard the spark plug.

Faint marks may extend from shell 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 very high voltage potential ionizes the air. The corona is a normal condition and is not an indication of leakage between the shell and the insulator.

Inspect the shell 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 the electrodes for excessive wear. Flat surfaces with sharp edges provide the best conditions for creating a spark. Cat spark plugs have precious metal tips on the ends of the electrodes 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 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 causing a misfire. Large deposits may retain heat which can cause premature fuel ignition and lead to uncontrollable detonation.

A standard ohmmeter (9 V) 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 (9 V) for measuring the resistance of other types of spark plugs. Measure the resistance between terminal post and electrode. Discard any spark plug with a wire-wound resistor if the resistance is outside the range of 1000 to 1500 ohms.

Cleaning the Spark Plug

Thoroughly clean the spark plug. Do not use a metallic wire brush. Glass beads are the preferred method for cleaning.

Follow these guidelines for the use of 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.

Installing the Spark Plug

Standard Ignition System

    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.

  1. Before installing the spark plug, set the electrode gap to 0.38 mm (.015 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.

  2. Ensure that the spark plug is clean and free of dirt and oil.

  3. Always use a new gasket when a spark plug is installed. If a used spark plug is installed orient the tab of the gasket toward the electrode. 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.


    NOTICE

    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.


  4. Install the spark plug by hand until the spark plug bottoms out. Tighten the spark plug to 38 ± 3 N·m (28 ± 2 lb ft).


    Illustration 4g02657458
    (1) Seal
    (2) Wire
    (3) Transformer assembly
    (4) Spark plug
    (5) Boot

  5. Inspect the boot and the wire. If the components are in good condition, install the components. If the components are not in good condition, install new components.

  6. Turn the ignition switch to the "ON" position.

CSA Ignition System



Illustration 5g02657478
CSA Ignition System
(6) Wiring harness
(7) Boot
(8) Transformer
(9) Copper washer
(10) Spark plug
(11) Spark plug gasket

  1. Install a new copper spacer on top of the spark plug. Install a new gasket onto the bottom of the spark plug. Install the spark plug by hand until the spark plug bottoms out. Tighten the spark plug to 38 ± 3 N·m (28 ± 2 lb ft).

  2. Screw the transformer onto the spark plug until the transformer is finger tight. Then tighten the transformer for an additional one-eighth turn (45 degrees).

  3. Inspect the boot and the wiring harness. If the components are in good condition, install the components. If a component is not in good condition, replace the old component with a new component.

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