the cause can be eliminated so that the failure will not repeated. Lets move into the failure analysis of con rod bearings.
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Analysis of Rod Bearing Failure
Bearing Failure due to lack of OilWhen insufficient oil flows to a bearing, actual metal to metal contact results. The bearing overheats, and the bearing metal melts or is wiped out of the bearing shell.Welds may form between the rotating journal and bearing shell. There is a chance that the engine will " throw a rod". This means the rod will "freeze" to the crankpin and break, and parts of the rod will punch a hole through the engine block. Oil starvation of a bearing could result from clogged oil lines, a defective oil pump or pressure regulator, or insufficient oil in the crankcase. Also, bearings with excessive clearance may pass all the oil from the pump, so other bearings are starved and will fail.
Fatigue failure of bearing
Bearing Scratched by dirt in the Oil
Bearing Failure due to taper journalIf the journal in tapered, one side of the bearing carries most or all of the load. This side will overheat and lose its bearing metal. With a tapered journal, both bearing halves fail on the same side. With a bent rod, failure will be on opposite sides.
Bearing failure from radius rideIf the journal to crank cheek radius is not cut way sufficiently when the crankshaft is machined, the edge of the bearing ride on the radius. This causes cramming of the bearing, possibly poor seating, rapis fatigue and early failure. Radius ride is most likely to occur on a reground crankshaft.
Bearing failure from improper seatingImproper seating of bearing shell in the bore causes local high spots where oil clearances are too small. Figure shows what happens when particles of dirt are trapped between the bearing shell and the bearing bore, This reduces oil clearances (As at X). Also an air space exists which prevents proper cooling of the bearing (A). The combination can lead to premature bearing failure. So care should be taken in connecting rod bearing installation and replacement.
Bearing failure from RidgingCrankpin ridging or camming may cause failure of a partial oil groove type of replacement bearing installed without removal of the ridge. The ridge forms on the crankpin because of uneven wear between the part of the crankpin in contact with the partial oil groove and the part that runs on the solid bearing. The original bearing wears around the ridge. However, when a new bearing is installed, the center zone may be overloaded (at the ridge) and may son fail. A ridge so slight that it can be enough to cause failure. Failures of this sort have been reported in engines having ridges of less than 0.001 inch (0.025 mm).
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