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Old 29th March 2010 | 23:08
  #70 (permalink)  
privateer01
 
Joined: Oct 2003
Posts: 125
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From: In an Airplane
Sure.

If the crankshaft were driven externally at rated speed without combustion taking place (as if an engine is shut down with a windmilling prop), then the master rod bearing sees only centrifugal loads.
Ok I get what your saying now.

I have an article discussing the very same thing (in different words).

When the Crank or rod goes concentric in the bearing bore.

The simple version is that when the shaft of the journal goes concentric in the bearing with no load.....the oil is not under the same forces and pressures.

This oil then begins to rotate with the shaft. When oil RPM between the bearing and journal reaches half the RPM of the shaft all cushion is lost.

The lack of cushion then allows the shaft (journal) to kiss the bearing.

Leading to bearing failure.

Our normal policy is that the only time the prop should drive the crank was short final....when wiping the power for landing.

Theory being this minimized the time the Journal could go concentric in the bearing

As a side note.....I've seen alot of failures after prolonged periods of disuse. It got so you could expect a failure within about 50 hrs if the engine had been sitting for a couple years. Even with proper pre-oiling
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