"Engine" essentially means "contraption", a mechanical assembly to carry out some complicated "works". Weaving engines, threshing engines, analytical engines, calculating engines, lifting engines, etc. Probably someone in 1750 made a pun about a lifting engine lifting an engine. It's an old word. Motor at least has a root involving "motive" as in motion as in auto-motive, self-moving. And so on. I bet it's a new word. If people know what you're talking about, it's the right word. "Boat anchor" sometimes works :-)