3306C Truck Engine Caterpillar

Check engine rpm with an accurate tachometer.

Low Idle Adjustment

Note: You can find the correct low idle rpm in the TMI.

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Personal injury can result from rotating and moving parts. Moving fan blades and moving parts will throw or cut any object or tool that falls or is pushed into them. Ensure that no one is working on, underneath or close to the machine before starting the engine. Ensure the area is free of personnel.

Start the engine, and operate the engine until the engine reaches the normal operating temperature. Check the low idle rpm without a load on the engine. If you need to make an adjustment, use the following procedure:

1. To adjust the low idle rpm, operate the engine with the governor in the LOW IDLE position:
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   Illustration 1	g00320512
   Low Idle Adjustment (1) Cover. (2) Low idle screw.

   1. Loosen the locknut for low idle screw (2) .

   2. Find the correct low idle rpm by turning low idle screw (2) .

   3. Then, increase engine rpm, and return to low idle rpm.

   4. Recheck the low idle rpm.

   5. Tighten the locknut.

Check Set Point (Balance Point)

Illustration 2	g00320607
6V-4060 Engine Set Point Indicator Group

An engine relies on set point (balance point) for the correct operation of the engine. An engine's set point is an adjusted specification. High idle rpm is NOT an adjusted specification.

Set point (balance point) equals full load rpm plus an additional 20 rpm. Set point is a measuring point that can be measured. At set point, the fuel setting adjustment screw and the first torque spring just begin to make contact.

At this rpm, the fuel setting adjustment screw and the first torque spring still have movement between the two components. When an additional load is put on the engine, the fuel setting screw or the first torque spring will become stable. These components stabilize after the initial contact with pressure.

Ultimately, the fuel setting adjustment screw and the first torque spring control the set point.

There is a new, more accurate method for checking the set point of the engine. Review the required tools for the new method. If these tools are not available, you can use an alternative method for checking set point.

You can use the 6V-4060 Engine Set Point Indicator Group with the 6V-2100 Multitach to check an engine's set point.

Note: See Special Instruction, SEHS7931 for instructions on the installation of this tool group and on the usage of this tool group.

Alternative Method for Checking Set Point

If the set point is correct and the high idle rpm is within specifications, the fuel system operation of the engine is correct. The set point for the engine is determined by these two factors:

• 20 rpm greater than full load rpm

• The rpm is obtained when the fuel setting adjustment screw and the torque spring begin to make contact.

Use the following procedure to check the set point:

Illustration 3	g00320609
Terminal Location (3) Brass terminal screw.

Note: See Special Instruction, SEHS7050, "Techniques for Loading Engines" for more information.

1. Connect an accurate tachometer to the tachometer drive.

2. Connect the clip end of the 8T-0500 Circuit Tester to brass terminal screw (3) on the governor housing.

3. Then, connect the other end of the tester to a place on the fuel system with a good ground connection.

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Personal injury can result from rotating and moving parts. Moving fan blades and moving parts will throw or cut any object or tool that falls or is pushed into them. Ensure that no one is working on, underneath or close to the machine before starting the engine. Ensure the area is free of personnel.

4. Start the engine.

5. With the engine at normal operating conditions, operate the engine at high idle.

6. Record the rpm of the engine at high idle.

7. Slowly add load to the engine until the circuit tester light just comes on.

   This is the set point.

8. Record the engine rpm at set point.

9. To ensure that the correct reading is found, repeat Step 7 for several times.

10. Stop the engine.

11. Compare the records from both Steps 6 and 8 with the information on the Engine Information Plate.

    If the Engine Information Plate is not available, see the TMI.

    The tolerance for the set point is ± 10 rpm. The tolerance for high idle rpm is ± 30 rpm. If the readings from both Steps 6 and 8 are within tolerance, no adjustment is needed.

Note: In some applications, high idle rpm will be less than the lower limit. This can be caused by high parasitic loads. Loads with hydraulic pumps and loads with compressors are good examples of high parasitic loads.

Adjusting Set Point (Balance Point)

If the set point and the high idle rpm are within tolerance, no adjustment is needed.

If the set point is not correct, follow these instructions:

1. Remove the cover (1), and loosen the locknut.

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Illustration 4	g00320610
Adjustment for Set Point (4) Adjustment screw.

2. Turn adjustment screw (4) in order to adjust the set point to the midpoint of the tolerance.

3. When the set point is correct, check the high idle rpm. The high idle rpm must not be more than the high limit of the tolerance.

   1. If the high idle rpm is more than the high limit of tolerance, check the governor spring and the flyweights.

   2. If the high idle rpm is less than the low limit of tolerance, check the governor for excess parasitic loads. Then, check the governor spring and the flyweights.

Dashpot Screw Adjustment

The dashpot screw adjustment does not normally need adjustment from the factory setting. If the engine is slow in changing rpm with a change in load, the dashpot adjustment screw may possibly need an adjustment.

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Illustration 5	g00390372
Dashpot Screw Adjustment (1) Dashpot adjustment screw.

1. Turn dashpot adjustment screw (1) clockwise until the dashpot adjustment screw stops.

2. Turn the dashpot adjustment screw (1) counterclockwise by 1/2 ± 1/4 turn.