3408C, 3412C and 3412D High Performance Marine Engines Caterpillar

Bridge Adjustment (If Equipped)

When the head is disassembled, keep the bridges with the respective cylinders. Adjustment of the bridge will be necessary for the following reasons.

• Grinding the engine's valves

• Resurfacing or reconditioning the engine's cylinder head

The bridge should be checked and/or adjusted when the valves have been adjusted. Use the procedure that follows to make an adjustment to the bridge.

Illustration 1	g00363479
Bridge adjustment

Note: Valves must be fully closed.

1. Apply engine oil on the bridge dowel in the cylinder head. Apply engine oil in the bore in the bridge.

2. Install the bridge with the adjustment screw toward the exhaust manifold.

3. Loosen the locknut for the adjustment screw. Loosen the adjustment screw for several turns.

4. Put a force on the bridge with a finger. This will keep the bridge in contact with the valve stem opposite the adjustment screw.

5. Turn the adjustment screw clockwise until the adjustment screw makes contact with the valve stem. Then, turn the adjustment screw 20 to 30 degrees more in a clockwise direction. This will make the bridge straight on the dowel. Also, this will make compensation for the clearance in the threads of the adjustment screw.

6. Hold the adjustment screw in this position. Tighten the locknut to 47 ± 9 N·m (35 ± 7 lb ft).

7. Use clean engine oil to lubricate the contact points of the bridge assembly and the rocker arm.

Valve Lash Setting

Valve lash is measured between the rocker arm and the bridge for the inlet valves. Valve lash is measured between the rocker arm and the valve stem for the exhaust valve. All of the clearance measurements and the adjustments must be made with the engine stopped. The valves must be fully closed.

Valve Lash Check

An adjustment is not necessary if the measurement of the valve lash is in the acceptable range. The ranges are given in the following tables.

Note: The inlet and exhaust valve lash adjustments should be made at the first recommended oil change. Refer to Operation And Maintenance Manual for subsequent intervals.

Valve Lash Adjustment

Illustration 2	g01015545
Cylinder and valve locations for 3408 engines (A) Inlet valves (B) Exhaust valves (C) Fuel injection pump

Illustration 3	g01015548
Cylinder and valve locations for 3412 engines (A) Inlet valves (B) Exhaust valves (C) Fuel injection pump

Use a feeler gauge in order to measure the valve lash setting.

Illustration 4	g00363480
Valve lash

To make an adjustment to the valve lash, turn the adjustment screw in the rocker arm. Valve lash adjustments can be made by using the following procedure:

Illustration 5	g00363481
Valve adjustment (typical example)

Adjust the valve lash while the engine is stopped. Use the following procedure in order to adjust the valves:

1. Put the No. 1 piston at the top center position.

   Note: See Testing and Adjusting, "Finding Top Center Position for the No. 1 Piston" for further details.

2. With No. 1 piston at the top center position of the compression stroke, an adjustment can be made to the valves.

   Before any adjustments are made, lightly tap each rocker arm at the top of the adjustment screw. Use a soft mallet to ensure that the lifter roller seats against the camshaft's base circle.

3. Make an adjustment to the valve lash on the inlet valves for the following cylinders.

   For 3408 engines, adjust the valve lash on the inlet valves for cylinders 1, 2, 5, and 7.

   For 3412 engines, adjust the valve lash on the inlet valves for cylinders 1, 3, 4, 6, 7, and 12.

   1. Loosen the valve adjustment locknut.

   2. Place the appropriate feeler gauge between the inlet rocker arm and the inlet valve bridge. Turn the inlet adjustment screw while the valve adjustment locknut is being held from turning. Adjust the valve lash until the correct specification is achieved. Refer to Table 3.

   3. After each adjustment, tighten the valve adjustment locknut while the valve adjustment screw is being held from turning. Use the following torque.

      Engines with a bridge adjusting assembly Torque for the valve adjustment locknut ... 30 ± 4 N·m (22 ± 3 lb ft)

      Engines without a bridge adjusting assembly Torque for the valve adjustment locknut ... 47 ± 9 N·m (35 ± 7 lb ft)

      Recheck each adjustment.

4. Make an adjustment to the valve lash on the exhaust valves for the following cylinders.

   For 3408 engines, adjust the valve lash on the exhaust valves for cylinders 1, 3, 4, and 8.

   For 3412 engines, adjust the valve lash on the exhaust valves for cylinders 1, 4, 5, 8, 9, and 12.

   1. Loosen the valve adjustment locknut.

   2. Place the appropriate feeler gauge between the exhaust rocker arm and the exhaust valve bridge. Turn the exhaust adjustment screw while the valve adjustment locknut is being held from turning. Adjust the valve lash until the correct specification is achieved. Refer to Table 3.

   3. After each adjustment, tighten the valve adjustment locknut while the valve adjustment screw is being held from turning. Use the following torque.

      Engines with a bridge adjusting assembly Torque for the valve adjustment locknut ... 30 ± 4 N·m (22 ± 3 lb ft)

      Engines without a bridge adjusting assembly Torque for the valve adjustment locknut ... 47 ± 9 N·m (35 ± 7 lb ft)

      Recheck each adjustment.

5. Remove the timing bolt, and turn the flywheel by 360 degrees in the direction of engine rotation. This will position the No. 1 piston at the top center at the beginning of the exhaust stroke. Install the timing bolt in the flywheel.

6. Make an adjustment to the valve lash on the inlet valves for the following cylinders.

   For 3408 engines, adjust the valve lash on the inlet valves for cylinders 3, 4, 6, and 8.

   For 3412 engines, adjust the valve lash on the inlet valves for cylinders 2, 5, 8, 9, 10, and 11.

   1. Loosen the valve adjustment locknut.

   2. Place the appropriate feeler gauge between the inlet rocker arm and the inlet valve bridge. Turn the inlet adjustment screw while the valve adjustment locknut is being held from turning. Adjust the valve lash until the correct specification is achieved. Refer to Table 3.

   3. After each adjustment, tighten the valve adjustment locknut while the valve adjustment screw is being held from turning. Use the following torque.

      Engines with a bridge adjusting assembly Torque for the valve adjustment locknut ... 30 ± 4 N·m (22 ± 3 lb ft)

      Engines without a bridge adjusting assembly Torque for the valve adjustment locknut ... 47 ± 9 N·m (35 ± 7 lb ft)

      Recheck each adjustment.

7. Make an adjustment to the valve lash on the exhaust valves for the following cylinders.

   For 3408 engines, adjust the valve lash on the exhaust valves for cylinders 2, 5, 6, and 7.

   For 3412 engines, adjust the valve lash on the exhaust valves for cylinders 2, 3, 6, 7, 10, and 11.

   1. Loosen the valve adjustment locknut.

   2. Place the appropriate feeler gauge between the exhaust rocker arm and the exhaust valve bridge. Turn the exhaust adjustment screw while the valve adjustment locknut is being held from turning. Adjust the valve lash until the correct specification is achieved. Refer to Table 3.

   3. After each adjustment, tighten the valve adjustment locknut while the valve adjustment screw is being held from turning. Use the following torque.

      Engines with a bridge adjusting assembly Torque for the valve adjustment locknut ... 30 ± 4 N·m (22 ± 3 lb ft)

      Engines without a bridge adjusting assembly Torque for the valve adjustment locknut ... 47 ± 9 N·m (35 ± 7 lb ft)

      Recheck each adjustment.

8. Remove the timing bolt from the flywheel after all valve lash adjustments have been made.