1987/09/01 Caterpillar

3406, 3406B Truck Engines

Reference: Truck Engine News, October 1985, Page 1, "Routine Mid-Life Roll-Ins Of Main And Connecting Rod Bearings No Longer Recommended. " Truck Engine News, September 1986, Page 2, "Bearing Failures On Engines Due To Lack Of Lubrication ".

For many years it has been the standard of the industry to replace main and rod bearings at mid-life. With the introduction of copper bonded bearings and improved quality crankshafts, mid-life bearing roll-ins are no longer recommended for 3406 Truck Engines in normal applications where the engine receives correct maintenance.

With increased speed limits across the U.S. it is timely to define the conditions under which to consider bearing replacements. This is due to the fact that road speed is a major cause of engine load and engine load and RPM are major factors in determining bearing life.

While rod bearing replacement may be considered at mid-life, main bearings in almost all circumstances should not be replaced until overhaul unless there has been lube system debris damage. The following conditions may suggest the need for mid-life rod bearing inspection/replacement.

1. Extended operation at high load factors below 2.35 km/L (5.5 mpg) for 3406B Truck Engines.

2. Extended operation at high speeds (2100 rpm and above).

Example Situations:

a. Extensive use of a Jacobs Brake.

b. Non-progressive shifting.

3. Marginal lube operation (see September 1986 Truck Engine News).

Example Situations:

a. Repeated cold starts below -1°C (30 °F) without a block heater or with SAE 30 oil.

b. Continual quick starts after oil change with either an empty oil filter or no prelubrication.

c. Repeated rapid starts to high idle rpm (to quickly fill air tanks, etc.).

4. Excessive sooting (see your Caterpillar dealer for an S ·O·S· analysis).

Example Situations:

a. Excessive black smoke (Fuel Ratio Control misadjustment and/or extended nozzle malfunction).

b. Low capacity oil filters (use of brands other than Caterpillar).

c. Extended oil change intervals (see chart).

Lube oil drain interval, see note.

NOTE: Not all oils in the CD classification have equal performance. This chart assumes that a superior quality oil has been selected. A lower quality oil would require that the change intervals be reduced accordingly.

5. Use of a poor quality crankshaft /ld/ If a crankshaft from another manufacturer was used during a previous repair, a poor bearing contact pattern may be encountered.

Because of the new speed limit, some 300 and 320 kW (400 and 425 hp) engines may now be candidates for rod bearing replacement, while rod bearings in most 230 and 260 kW (310 and 350 hp) engines will continue to last until overhaul.

There are several indicators that would suggest the need for an immediate inspection/replacement of the engine bearings.

1. Visible nonmetallic material in the filter (usually aluminum).

2. Extended operation with lube oil contamination from diesel fuel or antifreeze (see your Caterpillar dealer for an S ·O·S analysis).

3. Excessive lubrication system temperatures.

Example Situations:

a. Excessive operation of a BrakeSaver.

b. Cooling system overheating (loss of coolant).

4. Excessive lead and aluminum in oil (see your Caterpillar dealer for an S ·O·S analysis).

For engines operating in fleets it is suggested that some engines could be selected for rod bearing replacement for the purpose of "sampling" to determine whether mid-life bearing replacement is needed on the remainder of their fleet.