Ha, yeah that would be a special case.
Some more info for motors:
EPRI NMAC Repair and Reconditioning Specification Guidance for AC Squirrel-Cage and Salient Pole Synchronous Motors with Voltage Ratings of 2.3 to 13.2 kV Report 1016679 (also Revision 1 of 1000897). You can download for free (or the cost of giving up your email address)
here:
EPRI Motor Repair Spec said:
The fits between the bearing OD and housing shall be checked to ensure they are within the following limits. For thick shell bearings, unless otherwise specified by the motor manufacturer, such fits should be size-for-size to 0.001 - 0.002 ins. tight. For thin shell bearings such fits should be size-for-size to 0.002 in loose
... Thinking about why they (EPRI) might treat two types of bearings differently, I can speculate that maybe they don’t want the assembled shaft-bearing clearance to be sensitive to the housing fit, so for thin shell bearings (that might be significantly deformed by sturdy housing), they make it size-for-size or slightly loose. (but they still recommend plastigage checks with housing tightened which means you have to assemble the housing onto the bearing twice, once for plastigage check and again for final assembly). Or else there is some concern about stresses in the thin bearing clamped by interference, maybe with thermal expansion / differential expansion effects. Who knows.
But we do at least one motor where the OEM tells us to have a clearance 0-0.002”, even though the bearings are is clearly thick shell imo.
And the Electric Apparatus Services Association (respected trade organization for motor repair) says
EASA Technical Manual said:
Most electric motor sleeve bearings perform best with housing clearances of 0.001” to 0.003”
It seems like a bit of a hodge-podge on the electric motor side. So from my side, all I can say is punt: look to your OEM, or applicable standards, or experts in your particular equipment and bearing.
=====================================
(2B)+(2B)' ?