Chapter 11: Failure Analysis
103
A symptom of abrasive ingestion is smoky exhaust. As
the cylinder walls wear; pressure from the combustion
chamber blows by the piston and pressurizes the
engine sump. This overpowers the PCV valve and
allows oil to build up in the combustion chamber.
See Figure 11.4.
7. Abrasive materials that enter the engine get
absorbed by the oil and thicken it.
See Figure 11.5.
Figure 11.4
Figure 11.5
8. Because the oil absorbs the abrasive particles,
the engine components that are immersed in oil
will show definite signs of abrasive ingestion
especially around the connecting rod and main
bearing journals. See Figure 11.6.
NOTE: Abrasives that are trapped in the oil will
cause the lower portion of the combustion cham-
ber to wearing more than the upper portion.
NOTE: Wear of only one bearing surface on a
new engine could be a sign of a manufacturing
defect.
NOTE: Abrasive particles can also be imbedded
into materials that are softer than the abrasive.
This will cause the affected part to act like a
piece of sand paper or a grinding wheel.
See Figure 11.7.
Figure 11.6
Figure 11.7
Imbedded abrasives
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