G3408 and G3412 Engines Caterpillar

Restriction Of Air Inlet And Exhaust

If there is a restriction of the air inlet or of the exhaust system, horsepower and engine efficiency will be reduced.

Back pressure from the exhaust (pressure difference measurement between turbocharger exhaust outlet and atmosphere) must not be more than 686 mm (27 inches of H₂O) for turbocharged engines.

Measurement Of Exhaust Temperatures

Use the 1U-8865 Infrared Thermometer to check exhaust temperature. Instructions for the test procedures can be found in Special Instruction SEHS8149. These instructions are included with the infrared thermometer.

Checking Aftercooler Operation

Use the 4C-6500 Thermistor to check the operation of the aftercooler.

Refer to Special Instruction, SEHS8446 for more information about the 4C-6500 Thermistor .

Turbocharger

Inspect the bearing for the turbocharger. This bearing should be inspected after 7200 hours or service. This check should also be made if any unusual sound or vibration is noticed in the turbocharger. The turbocharger does not need to be disassembled in order to perform this quick check. Remove the piping from the turbocharger and inspect the compressor impeller. Inspect the turbine wheel and the compressor cover. Rotate the compressor and turbine wheel assembly by hand. Observe the compressor and the turbine wheel by feeling for excess end play and radial clearance. The rotating assembly should rotate freely with no rubbing or binding. The impeller should not rub against the compressor cover. The turbine wheel should not rub against the turbine housing. The turbocharger must be reconditioned, replaced, or rebuilt when any of the above conditions exist.

End clearance should be checked with a dial indicator. Attach a dial indicator with the indicator point on the end of the shaft. Move the shaft from one end to the other end. Take note of the total reading on the indicator.

End play for the turbocharger should be 0.08 to 0.25 mm (.003 to .010 inch). If the end play is more than the maximum end play, the turbocharger should be rebuilt or replaced. If the end play is less than the minimum end play, carbon may be built up on the turbine wheel. If this is the case, the turbocharger should be disassembled for cleaning and inspection.

Illustration 1	g00320945
Typical example of checking the end play of the turbocharger

A more reliable check of the bearing conditions can be made only when the turbocharger is disassembled. The bearings, the shaft journal, and the housing bore diameters can accurately be measured when the turbocharger is disassembled.

Illustration 2	g00320963
Checking turbocharger radial clearance (typical example)

Radial clearance can also be checked with a dial indicator. Remove the oil return line from the turbocharger. Attach a dial indicator with an indicator point that is extended to the shaft. The indicator point must be extended to a length that will allow the dial indicator to contact the shaft through the oil return hole. Make sure that the contact point is centered on the shaft. This will provide the highest indicator reading. Raise both ends of the shaft upward. Push both ends of the shaft downward in the opposite direction. The total movement of the indicator should be between 0.076 mm (0.003 inch) and 0.178 mm (0.007 inch). If radial clearance exceeds 0.187 mm (0.007 inch), or if the minimum clearance is under 0.076 mm (0.003 inch), the turbocharger should be disassembled and the bearings should be checked.

Note: Do not cock the shaft. A false reading will be obtained if the shaft is cocked.

Crankcase Pressure

Damaged pistons or piston rings that are broken or damaged can be the cause of too much pressure in the crankcase. This condition will cause the engine to run rough. A large amount of fumes may come from the crankcase breather due to this condition. This crankcase pressure can also cause the element for the crankcase breather to have a restriction in a very short time. If oil is leaking at the gaskets, or seals, there may be too much pressure in the crankcase.

Compression

5P-7307 Engine Turning Tool

An engine that runs rough may have a leak at the valves, or the engine may have valves that need adjustment. Run the engine at the speed that produces the rough running. Remove the wires from the transformers one at a time. This will help in detecting a cylinder that has low compression. This will stop the flow of current to that cylinder.

Repeat this process for each cylinder. When a wire is removed and the engine performance is not affected, the cylinder with low compression has been detected. Be sure to install the wire for the transformer at the proper times. Install the wire after each cylinder test, and before removing another wire. This test can indicate a faulty transformer. A malfunctioning spark plug can be found with this test as well. Continue to test the cylinder.

Condition of the valves, valve seats, pistons, piston rings and cylinder liners can be tested by checking the compression in each cylinder. Refer to the chart in the Operation and Maintenance Manual, "Every 750 Hours Cylinder Pressure Blowby" section.

This test will detect the cause of loss of compression in a cylinder. Removal of the head is necessary to find small defects. Inspection of the valves and valve seats is necessary to find those small defects. Repair of these problems is normally done when the engine is reconditioned.

Cylinder Head

The cylinder head has valve seat inserts, valve guides, and bridge dowels that can be removed. Replacement of these components can be made with the tools that follow.

Valves

Use the 5S-1330 Valve Spring Compressor and the 5S-1322 Valve Keeper Installer in order to remove a valve. These tools can be used to install a valve.

Valve Seat Inserts

The tools that are needed for removal and installation of the valve seat inserts are in the 166-7444 Valve Seat Extractor Tool Group. Refer to Special Instruction, SMHS7935. Lower the temperature of the valve seat insert before installing into the head of the engine. This will make the installation process easier.

Valve Guides

The tools that are needed in order to install the valve guides are the 5P-2396 Bushing and the 9V-7349 Driver Assembly. The counterbore in the driver bushing installs the guide to the correct height.

Valve Guide Bore

Illustration 3	g00580855
Valve Guide Gauge

Use the 5P-3536 Valve Guide Gauge Group in order to check the bore of the valve guides. Refer to Special Instruction, GMG02562 for complete instructions on the 5P-3536 Valve Guide Gauge Group .

Bridge Dowel

Use a 5P-0944 Dowel Puller Group with a 5P-0942 Dowel Extractor to remove the bridge dowels. Install a new bridge dowel with a 5P-2406 Dowel Driver. This dowel driver installs the bridge dowel to the correct height.

Bridge Adjustment

When the head is disassembled, keep the bridges with the respective cylinders. Adjustment of the bridge will be necessary after the valves are ground or other reconditioning of the cylinder head is performed. Use the procedure that follows to make an adjustment to the bridge.

Note: Valves must be fully closed.

1. Put engine oil on the bridge dowel in the cylinder head and 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.

4. Put a force on the bridge with a finger. Keep the bridge in contact with the valve stem that is opposite to the adjustment screw.

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Illustration 4	g00580860
Typical Example Of Bridge Adjustment

5. Turn the adjustment screw clockwise until contact is made with the valve stem.

   Turn the adjustment screw in the clockwise direction. ... 30 degrees

   This will make the bridge straight on the dowel. This will also compensate for the clearance in the threads of the adjustment screw.

6. Hold the adjustment screw in position and tighten the locknut to a torque of 28 ± 4 N·m (21 ± 3 lb ft).

7. Put engine oil at the point of contact between the rocker arm and the bridge.

Valve Clearance Setting

Note: Valve clearance is measured between the rocker arm and the bridge for the valves.

Note: If the valve clearance is adjusted, the bridge must be checked.

Illustration 5	g00580863
Valve Adjustment

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

1. Put the No. 1 piston at the piston top center position on the compression stroke. Refer to Finding The Piston Top Center Position For No. 1 Piston On The Compression Stroke for additional information.

2. Refer to the chart for the adjustment of the valves that have only two crankshaft positions.

3. Loosen the locknut for the adjustment screw on the pushrod. Turn the screw counterclockwise in order to increase the valve clearance.

4. Put a feeler gauge of the correct dimension between the rocker arm and bridge contact surface. Turn the adjustment screw clockwise until the valve clearance is set to the specifications in the chart.

5. After each adjustment, tighten the nut for the adjustment screw to a torque of 28 ± 4 N·m (21 ± 3 lb ft) and check the adjustment again.

Illustration 6	g00274783
G3408 Cylinder And Valve Location

Illustration 7	g00541847
G3412 Cylinder And Valve Location

Exhaust Bypass

Illustration 8	g00590746

On turbocharged engines, the exhaust bypass valve can be checked by measuring the inlet manifold pressure. The inlet manifold pressure is checked with the 1U-5470 Engine Pressure Group .

These engines are equipped with water cooled adjustable exhaust bypass valves. The specifications for the correct intake manifold pressure can be found at your local Caterpillar Dealer. The exhaust bypass valve is preset at the factory. Adjustments to this valve may be necessary for any of the following reasons: replacement of the bypass valve, a change in altitude and changes in ambient temperature conditions. The exhaust bypass valve should be adjusted for the maximum load that will be placed on the engine. The throttle angle will be between 60 degrees and 70 degrees from the closed position. This setting should give you minimum fuel consumption.

To adjust the exhaust bypass valve, remove the plug that is installed directly above the adjustment screw (5). Loosen the jam nut (4) and move the jam nut toward the end of the screw. Turn the adjustment screw in order to increase the manifold pressure. Turn the adjustment screw outward in order to decrease the manifold pressure. Once the final adjustment is made, turn the jam nut and lock the setting screw in place.

Information on intake manifold pressure will be given in measurements of absolute kPa. Use gauge pressure to measure the manifold pressure.

These engines have water cooled adjustable wastegates for variable turbocharger boost pressure. Refer to the charts in order to find the setting for the wastegate. This is in accordance with the operating altitude of the engine. The charts can also find the maximum angle of the throttle for a given load on an engine. High angles of throttle only require minimum fuel consumption. This minimum fuel consumption is for angles that are between 65 to 75 degrees.

The wastegate is adjusted by setting the engine to the maximum load. This load setting can be less than rated load. Refer to the chart for the correct load setting. Identify the engine model and the speed. The pressure differential between the turbocharger boost and the manifold pressure is located on the chart. Taps are available in the intake manifold for taking pressure measurements. Taps are also located in the boost line for the turbocharger.

The pressure that is measured should match the pressure that is in the charts. This is done by adjusting the wastegate. If the pressure is too low, turn the screw for the wastegate in the clockwise direction. If the pressure is too high, turn the screw for the wastegate in the counterclockwise direction.

The procedure that is described above pertains to the operating altitude of an engine. The wastegate may be adjusted up to any load that is less than the maximum allowable load. By using this procedure, the engine's fuel consumption will be minimized.