NH,
If you get the melting temperature of Al, it will melt, in the presence of steel or not. Probably what is happening if you can't seem to get the Al to melt off the motor rotors is because the steel is taking the heat and transferring it away from the melting area. You will need a bunch more heat input to get the complete rotor up to the melting point of Al if some of it is being transferred away into the steel shafts on each end, for example. Bottom line, you need more heat input to melt the bigger chunks.
If you have an acetylene torch you will have enough concentrated heat available to melt spots on the Al covered rotor because you can put the heat into the rotor fast enough so the Al will get up to melting temp before the steel can conduct it away.
Sounds like fun, especially if you have your young fella soaking in the experience.
Jon.
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