2000/04/01 Caterpillar

Engines:

G3408 (S/N: 6NB)

G3412 (S/N: 7DB)

Engine News SEBD9284, April 2000, "Correction To Testing And Adjusting Section, Spark Plug and Transformer Information". Disregard this article. The correction information follows.Systems Operation/Testing And Adjusting, SENR3088-01, "3408 And 3412 Natural Gas Engines, Testing And Adjusting Section", "Spark Plug And Tansformer". This module is part of Service Manual, SENR3085, "3408 And 3412 Natural Gas Engines (S/N: 6NB1-UP; 7DB1-UP)". The information is not correct. The correct information follows.

Spark Plug And Transformer

The following tools are needed:

• 2P-5481 Deep Well Socket

• 9V-6695 Strip

• 154-9521 Spark Plug Seat Cleaner

Illustration 1	g00579964
Altronic Spark Plug And Transformer (1) Transformer. (2) High voltage wire assembly. (3) Rubber boot. (4) Seal. (5) Spark Plug.

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NOTICE
The high voltage wire (2) and the seal (4) must be installed on all of the cylinders of an engine that is running. If this is not done, a spark from the exposed lead may ignite the vapors from the crankcase, this could result in damage to the engine.

Two different manufacturers of ignition systems have been used on the G3408 Engine and on the G3412 Engine. Altronic is the current manufacturer of Caterpilllar ignition systems. Fairbanks Morse was the manufacturer of the former ignition systems.

Illustration 2	g00646486
Externally mounted transformer

Illustration 3	g00712011
View A Location of the "U" cup seal. ((4)) "U" cup seal. ((6)) Adapter tube for spark plug. Dimension "X."

Be sure that the seal (4) is installed correctly. This seal should prevent any oil leakage from the crankcase. Oil leakage could enter the spark plug adapter.

Dimension "X" is the distance between the top of the "U" cup seal (4) and the top of the adapter tube (6) .

Dimension "X" is equal to the following amount. ... 5 ± 1 mm (0.20± 0.04 inch)

A magneto can have a transformer that is mounted externally, and a CDIS can have a transformer that is mounted externally. These ignition systems can have integral transformers as well. The integral transformers are installed on top of the spark plug.

Illustration 4	g00689968
Altronic Integral Transformer (7) Wire and Seal. (8) Band Clamp. (9) Boot. (10) Integral Transformer. (11) Spark Plug.

If the engine is equipped with the Altronic integral transformer, the spark plug (11) should be installed first. Ensure that the copper gasket is on the spark plug. Tighten the spark plug to a torque of 30 ± 4 N·m (22 ± 3 lb ft). Install the integral transformer (10). Tighten the integral transformer by hand. Tighten the integral transformer by an additional one-eighth of a turn. Do not exceed 6.75 N·m (5 lb ft) of torque.

Most magneto and the CDIS use an externally mounted transformer (1) with a secondary high voltage wire (2). This wire is between the transformer and the spark plugs (5). See Illustration 1.

Illustration 5	g00648705
Earlier Version Of The Fairbanks Morse Spark Plug And Transformer (12) Transformer. (13) Copper spacer. (14) Spark plug.

Illustration 6	g00648710
Later Version Of The Fairbanks Morse Spark Plug And Transformer (15) Rubber boot. (16) Seal.

This transformer and plug assembly is an integral unit. This assembly is mounted in the adapter in the cylinder head. The transformer (12) and the spark plug (14) are assembled together before installation in the adapter.

The torque for the assembly is the following amount. ... 47 ± 3 N·m (35 ± 2 lb ft)

Note: On engines that are equipped with a magneto, the copper washer that is supplied with the spark plug (8) must be removed. Install a copper spacer (13) on a new spark plug (14) .

The amount of voltage that is needed in order to cause the spark will change. This change will occur with a change in the conditions of the spark plug. Changes in engine load may also change the amount of voltage that is needed to cause the spark. A new spark plug will use 3,000 to 6,000 volts in an engine that is operating at low idle. At full load, this voltage will be 8,000 to 10,000 volts. The voltage that is needed in a spark plug that has a gap adjustment is 10,000 volts. Spark plugs will cause the engine to run roughly, if the spark plug voltage needs to be increased to 10,000 volts.

Spark plug gap must be kept at 0.380 mm (0.015 inch). The 9U-6695 Firing Indicator is an aid for detecting ignition problems. Follow the instructions that come with the tool.

Spark plugs must be installed to the following torque of 30 ± 4 N·m (22 ± 3 lb ft) with the 2P-5481 Deep Well Socket. Tighten the transformer by hand. Tighten the transformer by an additional one-eighth turn. Do not exceed 6.75 N·m (5 lb ft).

Do not overtighten the transformer or the spark plug.