i see the rule of thumb is to double the breakin period if u got new bearings.
why?
i also hear that a good used bearing is better then a new bearing.

 

Basically, when a bearing is being pressed in there is a good chance it won't go in perfectly straight and a slight high spot will be raised on the surface of the bearing (along with a corresponding and unimportant low spot).

You can minimize this issue longer break in issue by providing proper clearance before the engine is assembled.

One way to do this is taking a die grinder and 600grit paper in a split mandrel and "flapping" the bearing ID with the speed high enough it is self centering. Once you get real close to the desired clearance you can switch to finer grits.

This will take of high spots and when you do it right take off a bit more material at the ends of the bearings where contact from e-shaft flex first becomes an issue (as in why the RX-8 rear main journal is tapered).

Another fancy way to clearance the bearings is to mock up the e-shaft and rotors in a lathe with some fine rubbing compound suspended in oil and spin that until the proper clearance is achieved.

 

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