CRANKSHAFT BEARING REPLACEMENT GROUPS 1S7584 - Caterpillar

Introduction
The article below explains the proper interpretation of oil samples that are taken from 770G and 772G Off-Highway Truck (OHT) engines. The oil samples that are taken from these engines have shown some unique characteristics. These characteristics could be misunderstood. A misinterpretation of the results from the oil sample could lead to unnecessary inspections or repairs. The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.Problem
Oil samples taken from 770G and 772G engines have shown highly elevated values of potassium and aluminum. The elevated values may occur during the first thousand hours of operation. After the first thousand hours of operation, the potassium (K) and aluminum (Al) will slowly decrease to more typical levels.The source of these elements has been traced to the brazing flux that is used to manufacture the aluminum Air-to-Air Aftercooler (ATAAC). The brazing flux is made from a compound that contains a high concentration of potassium and aluminum. Residual amounts of this flux remain in the new ATAAC. Air from the turbocharger flows through the ATAAC during operating conditions. Moisture in the air reacts chemically with the brazing flux. This reaction releases small amounts of potassium and aluminum into the air stream. The potassium and aluminum enter the engine oil through the combustion air and the oil film on the cylinder liners.In oil sample analysis, potassium (K) is commonly used as an indicator of coolant contamination. Aluminum (Al) is commonly used to indicate severe bearing wear and dirt entry. The correct interpretation of the oil sample is difficult when elevated values of potassium and aluminum are present.Solution
Potassium and aluminum from the core of the ATAAC do not cause abnormal wear of the engine. Iron, lead, and chromium values are not affected by this source of potassium and aluminum. The service life of the core of the ATAAC is not reduced by the reaction with the brazing flux.Potassium could reach 200 parts per million and aluminum could reach 100 parts per million during the first thousand hours of operation. The ratio of potassium to aluminum is about 3 to 1 in most samples. After the first thousand hours of operation, the potassium and aluminum will slowly decrease. Potassium will eventually reach 25 parts per million or less. Aluminum will eventually reach 10 parts per million or less.Elevated potassium from the ATAAC brazing flux will make the identification of coolant contamination more difficult. Most heavy-duty coolants contain high concentrations of sodium and/or potassium compounds. Sodium and potassium results are used to determine if coolant has entered the engine oil. An indicator of coolant contamination in the oil sample is 25 parts per million or more of sodium and/or potassium. The ATAAC brazing flux may temporarily elevate potassium levels. If there are elevated levels of potassium, the analyst must use other indicators to determine if the engine oil has been contaminated with coolant. The following items are other indicators of coolant