1979/01/10 Caterpillar

Check The Adjustment Of The Original Tachometer Before A New Tachometer Is Installed


Industrial and Marine Engines

The 3N7288 and 3N7799 Electric Tachometers used on industrial and marine engines can be adjusted. In the past, there have been many new tachometers installed as replacements, when all that was needed was an adjustment to the original tachometer. Before a new tachometer is installed, use the procedure that follows to tell if an adjustment can improve the accuracy of the original tachometer.

1. Install a 5L8164 Dual Drive Adapter on the engine, and connect the sending unit of the tachometer to one output of the dual drive adapter.

2. Connect the sending unit of another tachometer, that is known to read correctly, to the other output of the dual drive.

3. Start the engine and check accuracy of the original tachometer with the reading of the tachometer that is known to be correct.

NOTE: There have been three different types of adjusting screws used on the 3N7288 Tachometers. The three different types are shown in Illustrations 1, 2, and 3.

4. Turn the adjusting screw on the back of the original tachometer until the readings are the same. The tachometer can be adjusted 7.5% of full scale in either direction. Clockwise (CW) rotation will give a reduction in the RPM reading. Counterclockwise (CCW) rotation will give an increase in the RPM reading.

Illustration 1. Location of adjusting screw.

Illustration 2. Location of adjusting screw.

Illustration 3. Location of adjusting screw.

NOTE: If the 5L8164 Dual Drive Adapter cannot be installed on the engine, it is possible to use the 1P5500 Phototach Group to check RPM.

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