Genuine Cummins Engine Air Compressor 3974549 Replacement For Sale

1. Preparation

Drain Fluids: Drain the engine coolant completely to avoid spills when removing the compressor's liquid-cooling lines.

Depressurize: Ensure the air system is fully bled of pressure by opening the drain valves on the air tanks.

Battery Safety: Disconnect the negative battery cable.

2. Disconnection

Line Removal: Disconnect the coolant supply and return lines, air discharge line, and the unloader line (if applicable).

Oil Lines: Disconnect the oil supply line, this compressor receives lubrication directly from the engine oiling system.

Brackets: Remove any support brackets attached to the rear or side of the compressor. Failure to reinstall these brackets later can lead to the compressor vibrating and cracking the timing gear housing.

3. Removal and Installation

Unbolting: Remove the four main mounting capscrews that secure the compressor to the engine gear housing.

Gear Timing:

For many applications, such as the Cummins 4B/6B, you must align the timing mark on the compressor gear (often a "9 o'clock" position or matching an "X" mark) to ensure the engine remains balanced.

Note: Some newer models do not require specific timing; check your specific Engine Serial Number (ESN) if you are unsure.

Gasket Replacement: Always use a new gasket between the compressor and the mounting flange. Clean both surfaces thoroughly to prevent oil leaks.

Installation: Slide the new compressor into place, ensuring the drive gear meshes correctly with the engine gear.

4. Finishing Steps

Torque Specs: Tighten the mounting capscrews to 40–45 ft-lbs.

Reconnection: Reattach all air, oil, and coolant lines using the following torque guidelines where applicable:

Oil supply fitting: 142–159 in-lbs.

Coolant fittings: Less than 310 in-lbs.

Air discharge fitting: 81–96 ft-lbs.

Refill: Refill the engine coolant and check for leaks once the engine is started.

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