[Jamesp]

From what I've seen, and this is simply gut feeling with - NO DATA - so I normally wouldn't say it,... the OEM single row bearings are adequate for the loads provided they have uncompromised grease lubrication. The dual rows are overkill and because of the additional load carrying capacity, can tolerate poor lubrication over a much longer time. Bearings tend to fail in an exponential manner. That means small changes in RPM, load, or other variables can lead to quick failures. I studied a case of police car alternator bearing failures. Turns out the additional electrical loads on a police car at idle was killing the batteries because the alternator could not keep up at idle. The solution?, a smaller alternator pulley so the alternator turned faster at idle. Going down the freeway those alternators were turning plenty fast. The result was repeatable bearing failures in the alternators.