How do bearings work?, Aluminum case expansion Options

[worn]

Calling the experts and anyone else. The case with the holes is aluminum. The crank, cam and lifters are steelish. As the case heats up the holes expand at twice the rate of the steel parts within. So how are for example main bearing clearances maintained as I open the throttle on the ribbon of highway that lies ahead. Shouldn't oughta work. Are they extra tight to start out with? (IMG:style_emoticons/default/unsure.gif)

[VaccaRabite]

1) tolerance is designed so that the clearance is acceptable at cold and hot to have oil pressure in the proper range. You can be out of spec but have good cold oil pressure that falls on its face when the engine is hot.
2) expansion at the center is relatively small. Expansion is not linear.
3) the engine heats up from the heads in, not the crank out. And the center of the engine will be roughly oil temp instead of the outside of the engine which will be roughly head temp. Less expansion at 200 then at 390.

Zach