1987/04/20 Caterpillar

3500 Family of Engines

Reference: Service Magazine; November 19, 1984; Page 12; "Additional Information For Correct Fuel Injector Timing".

Reports indicate there has been some confusion about the adjustment of the fuel injection timing dimension on the 3500 Family of Engines. In most cases, familiarization with the service manual timing procedure will help eliminate confusion and errors. The above reference article and the Service Manuals for the 3500 Family of Engines include a procedure for correctly setting fuel injection timing. An incorrect fuel timing dimension may be a result if the procedure is not precisely followed. Incorrect fuel injection timing can cause a variety of engines problems such as increased exhaust smoke, high exhaust temperatures, piston failures, etc.

The 6V3075 Dial Indicator is used in the 6V7880 Timing And Fuel Setting Tool Group. The dial indicator is used to measure the fuel setting and the fuel injection timing. When the stem of the dial indicator is pushed into the indicator housing, the large pointer on the face of the indicator will rotate clockwise. Reading clockwise, the positive numbers are black. When used to measure fuel setting, positive increases on the dial indicator correlate to increases in the fuel setting. However, when the dial indicator is used to measure the timing dimension, a positive increase on the dial indicator correlates to a decrease in the timing dimension. This has led to confusion that has resulted in injector timing set in the wrong direction from the 6V3117 Gage Block reference of 87.00 mm.

The following is an alternative fuel injection timing procedure which may be less confusing and easier to understand. In this procedure, the 8T1000 Electronic Position Indicator Group is used instead of the dial indicator.

1. Connect the 8T1002 Probe to the 8T1001 Indicator. Press the "ON" touch switch to turn the indicator on. Press the "+" and "mm" touch switches.

2. Install the 8T1002 Probe in the timing fixture with the collet loose.

3. Place the timing fixture and probe on the 6V3117 Gauge. Position the probe at the approximate midpoint of its travel and tighten the collet.

4. Push the "ZERO" touch switch on the indicator. The indicator is now set to show 0.00 mm with a 87.00 mm timing dimension. Different timing dimensions will show as a direct reading (deviation from 87.00 mm) on the indicator. For example, a timing dimension of 87.70 mm will show +0.70 mm on the indicator and a timing dimension of 86.80 mm will show -0.20 mm on the indicator.

5. Remove the timing fixture and probe from the gage. Move the probe stem by hand to check that the needed timing dimension can be reached (be sure the probe stem does not run out of travel before needed timing dimension is reached). If the timing dimension cannot be reached, loosen the collet and repeat Steps 3 through 5.

After Steps 1 through 5 are completed, the tooling is ready to use to check and adjust the timing dimension on the engine.

If the 8T1000 Electronic Position Indicator Group is not available, be sure to exercise care using the 6V3075 Dial Indicator.

Remember the key points that follow.

1. The smaller the timing dimension, the more advanced the timing.

2. Advancing timing beyond specification can increase mechanical stress on engine components.

3. Retarding timing beyond specification can increase black exhaust smoke and increase exhaust temperatures.