The process of tearing down and rebuilding an engine, which should include changing all the bearings, needs to have an option for reviewing bearing damage. In this follow-up to last weeks LubeTalk... we'll take a look at fillet rides, hot shorts, wiping and oil starvation diagnosis.

A condition most often seen when a custom or high-performance crankshaft is installed without a correction in the bearings is fillet ride. To increase the strength of the crankshaft, extra material is added to provide a larger radius between the journal and the counter weight to reduce stress in the component. The bearings must allow space for this extra material. If it doesn’t, the fillet of the crank will rub directly on the bearing. This will appear as excessive wear on the extreme edges of the bearings. The new bearings or the crank must be machined to provide the additional space. Many special high performance bearings are manufactured in this way for these applications.

A condition that results in a delamination of the bearing material is called a "hot short," where an excessive amount of heat builds up in the bearing. The lead in the lining of the bearing melts, resulting in large patches of bearing lining lifting from the surface. At first, this tends to look like a manufacturing problem. Any form of stress resulting in wiping and friction causing high bearing temperature is known to cause it.

Wiping is an early sign of future problems. This occurs when the crank begins to break through the oil film and contacts the bearing. This will result in a highly polished and slightly worn bearing surface. Uneven patterns in the bearings show alignment problems or a bent crankshaft or rods. Corrections for this include increasing oil pressure, reducing oil temperature, or switching to higher viscosity oil.

The last condition to mention is oil starvation. This can be seen as a more advanced stage of wiping, usually occurring first near the center of the bearing. The bearing will look very shiny or, in advanced cases, discolored, and will most probably have excessive wear all over. This condition is easily the most recognizable. Causes include insufficient oil clearance, plugged oil passages, blocked oil filter, incorrect oil for the application, incorrect oil pan design, incorrect placement of the oil pump pickup, or a malfunctioning oil pump.

To correct this problem, the incorrect, failed, or blocked part must first be diagnosed. Then, it becomes necessary to run a check of the affected parts to determine if they can be used again. Finally, a careful recheck of tolerances and clearances before reassembly should finish the preparation.

The bearings at the end of the season should look like they have little to almost no detectable wear. If everything works together correctly, the bearings should have little or no contact with the crankshaft.

One of the best ways to extend bearing life is to run up the oil pressure before starting the motor every time. Too often, the ignition is on as soon as the starter begins cranking. The motor starts before the oil has reached the bearings and this is where a high percentage of total bearing wear occurs. This wear can greatly be reduced if the ignition switch was turned on after oil pressure is achieved.

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