As for prep on an engine, probably against all body work paint guy's knowledge and training but based on experience is the reason you do not use any primer is because thats what is effected by temperature and creates a soft bed for the paint to delaminate from, or crush into, especially a filler, maybe you could use a thin coat of etching primer but your waisting your money on an engine, we just hose the engine off using the paint gun with acetone, let it dry and spray it, no prep at all when compared to painting sheetmetal, the paint clings like mad, I painted an engine for a T-28 Trojan that went on to win golden wrench award at oshkosh airshow in this fashion. good point about the safety issue's however, I just stand upwind! isocianates? I don't need no stinking suit! cough, cough, weez.......
And I agree any good enamel will work and won't kill you and/or your neighbors, here in southern california it is SO illegal to spray good paint anymore it isn't worth it, I'll use enamel from now on in fact, thanks for bringing up those issues guy's.
Aloha
