2004/07/01 Caterpillar

Engine:

G3606 (S/N: 3XF1-211)

G3608 (S/N: 4WF1-233; BEN1-218)

G3612 (S/N: 1YG1-235)

G3616 (S/N: BLB1-200; 4CG1-235)

Description of Change:

Illustration 1	g01087064
Typical example of a turbine wheel

Illustration 2	g01087065
(1) Accumulation of deposits on the turbine wheel

Certain operational practices and maintenance practices can prevent major damage to the turbocharger. This will also extend the service life of VTC254 turbochargers that are used on some G3600 engines.

The accumulation of deposits on the turbocharger's turbine blades is the main failure mode of the VTC254 turbocharger on G3600 engines. Refer to Illustrations 1 and 2. The deposits can accumulate more in one area or pieces of the deposits can break loose from the blade. This causes the turbine wheel to become unbalanced. This imbalance causes the shaft to move.

Once the shaft is able to move, the oil film that is between the rotating shaft and the shaft bearings degrades. This leads to failure of the shaft bearing. Once the shaft bearing fails, the blades on the turbine and on the compressor can come into contact with the turbocharger housing.

Analysis of Trends in Engine Data

As deposits form on the turbine blades, the efficiency of the turbocharger is slowly degraded. The G3600 control system adjusts for changes in efficiency of the turbocharger by closing the wastegate which forces more exhaust gas through the turbocharger. This allows the turbocharger to maintain the desired manifold pressure and the desired air/fuel ratio. The general condition of the turbocharger can be determined by monitoring and by recording engine data and analyzing the trends indicated by this data. The most critical parameters that must be monitored are the following:

• Inlet manifold air pressure

• Operation of the wastegate

• Indicated engine load

Additionally, these other parameters must also be monitored:

• Inlet air restriction

• Emissions NO_x

• Inlet manifold air temperature

• Fuel quality (fuel correction factor)

• Ambient air temperature

• Humidity

• Barometric pressure

• Turbocharger speed

The number of items that are recorded determines the accuracy of the prediction of the turbocharger's condition. The data from different engines cannot be compared due to the following factors:

• Different sites

• Arrangement of the engines

• Variations of the inlet air ducts and of the exhaust ducts

Comparative data must be taken under controlled conditions. The monitoring must be started with the following components in good condition:

• A clean turbocharger

• A tuned engine

• Air cleaners

• Spark plugs

Analysis of the data must take into consideration the condition of the engine and of the air filters. Incorrect analysis can result from data that is taken when the air filters are dirty or when a cylinder misfire is present. Monitoring trends for determining the maintenance intervals of the turbocharger requires careful planning and the careful collection of data. Maintenance costs for the turbocharger can be reduced as more data is collected and as experience is gained in analyzing the trends of the data.

Monitoring of Vibration

Monitoring of vibration is another method of determining the condition of the turbocharger. The monitoring of vibration shows the effects of accumulation of deposits on the turbine blades. An accelerometer is mounted on the exhaust inlet of the main housing. This is done by drilling and tapping the housing. This port must be made horizontally to the shaft centerline.

The measurements must be taken over a frequency range of 300 Hz to 1000 Hz. The measurements can be taken periodically or the measurements can be taken continuously. Continuous measurements must be controlled by the programmable logic controller (PLC). Setpoints must be programmed for the alarm and for shutdown.

Start monitoring the vibration of a new turbocharger. A baseline must be taken at the begining of the monitoring program. The baseline must be taken at a specific speed and load point. This data is used for comparison. This will allow you to see changes in the amount of vibration that is measured. The actual limits vary with different engines and with the condition of the site. For continuous trouble free operation, the root mean square (RMS) velocity will have a measurement of below 3 mm/s² (0.118 inch/s²). Under transient conditions a RMS velocity of 4.5 mm/s² (0.177 inch/s²) is acceptable. A RMS velocity of 6 mm/s² (0.25 inch/s²) indicates heavy rotor imbalance and the engine must be shutdown.

For a monitoring program, consider setpoints of 3.1 mm/s² (0.125 inch/s²) for the alarm and 3.8 mm/s² (0.150 inch/s²) for the shutdown. After experience is gained with the particular application the limits may be raised. You can raise the limits only if the inspections of the turbocharger indicate that raising the limits can be done without the risk of damage to the engine. In most cases 5 mm/s² (0.20 inch/s²) is considered the maximum allowable vibration shutdown point. Any value above this point will eventually result in severe damage to the turbocharger.

Cleaning of the Turbocharger

Testing has shown that the service life of the turbocharger and the service life of the cylinder head is improved by injecting a mixture of 15 percent ethylene glycol and of 85 percent deionized water into the intake manifold of G3600 engines. The injection process cleans the following components:

• The combustion chamber of the cylinder head

• The piston crown

• The valves

• The turbocharger's turbine blades

In order to prevent large deposits from breaking loose, this procedure must only be used on clean heads and turbochargers.

Old lines from the oil mister pump and a small auxiliary pump can be used to inject the glycol and water. However, the old lines from the oil mister pump are not made of stainless steel. Because the lines are not made of stainless steel, the lines will corrode. This will clog the spray nozzle. Kits from outside suppliers are available for installation.

The cleaning is performed while the engine is operating at full load or near full load. The cleaning is accomplished by injecting approximately 20 gallons of the mix. The mix must be injected once in every two weeks. The operator will determine the following maintenance practices:

• Frequency of cleaning

• Flow rate

• Amount of solution that is needed

Note: The injection procedure has not been tested on engines that are equipped with a catalyst. Caterpillar does not recommend injection procedure for applications that have a catalyst.

Adaptable To: The analysis of trends in engine data, the monitoring of vibrations and cleaning of the turbocharger are adaptable to all G3600 engines that are equipped with the turbocharger groups in Table 1.