1990/11/12 Caterpillar

Adjustable Exhaust Bypass Group Used; Provides More Precise Ability To Set Exhaust Pressure {1057}

Usage:

3406 ( 4FD ) Spark-Ignited Engines

An adjustable exhaust bypass group is used on the 3406 Spark-Ignited Engines. The adjustable bypass valve provides more precise ability to set the exhaust pressure as compared to the former spacer plate design. The new exhaust bypass group also has a water-cooled housing which provides longer life for the valve stem.

The new 7C9043 Exhaust Bypass Group is effective with 3406B Spark-Ignited Engine 4FD1.

Use the following procedures to adjust and/or replace the exhaust bypass group. Use the procedures in conjunction with the valve displacement values provided to set the bypass valve. Also, use the chart to change the valve displacement values based on the ambient temperature and/or attitude at which the engine is operating.

Replacement Procedure For Adjustable Exhaust Bypass Valve

The following steps are for replacement of the exhaust bypass valve.

NOTE: When replacing an adjustable bypass valve, the part will be marked "NON-CURRENT SETTING".

1. Loosen jam nut (2).

2. Find the prescribed valve displacement from the charts in 3406 SITA Adjustable Bypass Valve Settings by locating engine model, speed (rpm), and separate circuit aftercooler water temperature (SCAC), and the BkW (BHP) output for the engine.

3. Place the bypass valve in the bench fixture and apply 100 kPa (14.5 psi) air pressure to air inlet ("boost inlet") port (1).

4. Turn bypass valve adjustment screw (3) until the bypass valve movement meets the prescribed valve displacement from the zero gauge pressure position. Turn the screw counterclockwise (CCW) to increase displacement. Turn the screw clockwise (CW) to decrease displacement.

5. Tighten jam nut (2) after the setting is complete.

Exhaust bypass valve.

Adjustment Procedure For Adjustable Exhaust Bypass Valve

The following steps are for the adjustment of the exhaust bypass valve to compensate for altitude and/or ambient air temperature.

1. Loosen jam nut (2).

2. Place the bypass valve in the bench fixture and apply 100 kPa (14.5 psi) air pressure to air inlet ("boost inlet") port (1).

3. Find the prescribed valve displacement from the charts in 3406 SITA Adjustable Bypass Valve Settings by locating engine model, speed (rpm), and separate circuit aftercooler water temperature (SCAC), and the BkW (BHP) output for the engine.

4. Decrease the prescribed value displacement by the amount referenced in the Altitude And Temperature Table For Adjustable Bypass Valves.

5. Turn bypass valve adjustment screw (3) until the bypass valve movement meets the the valve found in Step 4. Turn the screw counterclockwise (CCW) to increase displacement. Turn the screw clockwise (CW) to decrease displacement.

6. Tighten jam nut (2) after the setting is complete.