JetPack,


The melting point of aluminium is significantly higher, at 660ºC, or 1,220ºF.

However, it rapidly becomes softer (its hardness is decreased) as its temperature rises.

At 450ºF it will be significantly more prone to bending and warping, as a result of the efforts to remove the bearing, than it would be at 250ºF.

Also, cast aluminium is often subjected to [link=http://www.csiro.au/news/ps196.html]heat treatment[/link].
This endows the casting with improved hardness and durability.

Heating the casting excessively can dramatically reduce the effect of that treatment; and thus weaken the metal.