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Your crankshaft bearings are protected by the hydrodynamic principle.It is a hard and fast law,.001 clearance per inch of shaft diameter,which is why model a rod and main bearings are ideally clearanced at .0015.
The stock model a crankshaft is dynamically balanced but does not have offset weights to counter balance power stroke impulse.
At maximum rpm,this power stroke impulse results in a flexing of the crankshaft (according the the late Herm Kohnke) as much as .001 flex at the center main bearing,resulting is a loss of the hydrodynamic principle and a failure of the bearing.
If you run an harmonic balancer it helps reduce this potential damage,also a lube line directly from the oil pump with a full flow filter down stream helps pressurize the center main bearing,providing some protection from the loss of the hydrodynamic principle that occurs.