tAll alternators are motors and all motors are alternators. Just spin them backwards that's it.
This is not exactly true. All motors are GENERATORS would be the correct term. An alternator is a totally different animal, it is a large electromagnet, so requires a current that creates a powerful magnetic field. A generator can be spun by hand and generates a small amount of power compared to an alternator. When an alternator is generating a full field it can take up to 20hp just to turn it, but the benefit of that is they can generate well over 100 amps while a similar sized generator can only generate a few amps. (for short periods, then they overheat and fry)