1987/09/14 Caterpillar

3400 Family Of Engines

Reference: Service Magazine; October 14, 1985; Page 7; "Routine Mid-Life Roll-Ins Of Main And Connecting Rod Bearings No Longer Recommended." Service Magazine; September 8, 1986; Page 7; "Bearing Failures On Engines Due To Lack Of Lubrication."

With the introduction of copper bonded bearings and improved quality crankshafts, mid-life bearing rollins are no longer recommended for engines in normal applications where the engine receives correct maintenance.

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 center and rear main bearings on the 3412 Engine should be inspected if the engine normally operates at high speed (2100 rpm and above). 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. Above 7.5 L (2.0 U.S. gal.) fuel/cyl/hr. fuel consumption for other applications (i.e., 3412 ... 90.8 L (24.0 gal.) fuel/hr; 3408 ... 60.6 L (16 gal.) fuel/hr.

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

3. Marginal lube operation (see September 8, 1986 Service Magazine).

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).

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.

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

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.

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.