PLATE AS 4185520 - Caterpillar

Inspecting the Spark Plug
Illustration 4 g00787368
(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, 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 very high voltage potential ionizes the air. 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.
Illustration 5 g00787372
(6) Precious metal tips on the electrode and the ground strap Caterpillar 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 systemA 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.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.
Use new glass beads for each set of spark plugs.
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.Checking the Spark Plug
After the spark plug is clean, measure the spark plug's resistance. If the resistance is correct, make sure that the electrode gap is correct before you install the spark plug.Note: A standard ohmmeter cannot be used for measuring the resistance of a used spark plug.Use the 142-5055 Insulation Tester Group to measure the resistance of the spark plug. Follow the warnings and instructions that are provided with the tool.Connect the red lead of the tester to terminal post (1). Because the ground strap is close to electrode (5), you will need to connect a smaller lead to the center electrode. Then connect the black lead of the tester