I found out the hard way that the trouble with used motors and surface finishes is that some of the alloys (aluminum or iron based) are slightly porous. This means they suck up some oil and grease into the surface... so you can get that sucker to look clean, and wipe it down with acetone or alcohol or brake cleaner, and it feels clean, but leave it sit a day and it's greasy again. This plays hell with getting finishes to stick... baking it or hot tanking it would be ways to help cure this....
However, for basic cleaning varsol/mineral spirits seems to do pretty good, a little bit more bite than kerosene, smells too though.
Beware of oven cleaners, lots of them have sodium hydroxide in (AKA Lye, drain cleaner) and while this works darn good, you don't want to leave it on aluminum based alloys very long or it will pit them and create flammable gases which could be a problem in the case of large areas of metal. On the other hand, you can just put a few spoons of lye in a big tub of hot water and dunk stuff in it, (wear gloves) as long as you don't leave it in more than a couple of minutes, then rinse right away.