"The engine does work."
Translation:המנוע כן עובד.
No. When you say "doesn't" in English it's just the way of expressing the negative, whereas when you say "does" in a positive statement, it expresses an emphasis which is expressed using "כן" in Hebrew.
Or with the verb "to be", we use voice intonation to express the emphasis:
I am happy! = !אני כן שמח
I don't know if in Italian you can say "si che sono felice", but as you know Spanish, it's like "Sí que estoy feliz".