So beyond fuel another thing I know kills bearings is aggressive triggering under no load...Rapid spikes in the engine RPM will cause the balls to skid instead of roll, and once the balls start skidding they start creating flat spots on the balls and or channels in the outer race, once it happens once it can happen easier the second time and easier the third time.....Bearings are especially vulnerable when the engine is cold....obviously combine this abuse with a low grade lubricant and the issue is compounded.. I have worked with several drivers who have a nervous trigger finger and they are always hurting bearings..either out of nerves or anger rapid hits of throttle while the tires are off the ground is a very bad thing for these engines...