JFD,
what kind of engines are you inquiring about...car engines? If you are referring to motorcycle engines, there is a guy in Puerto Plata, Mehia, that rebuilds motorcycle engines and i believe small outer board boat engines. He's good.
For big generators, there is a guy, Juan Carlos, and his father, they rebuild and service big generators. They're well known.
For cars, I'm sorry, i'm afraid i have no idea.
PS. I have the telephone numbers for both of these people if you need it.
Frank