No labor costs to build engines.
THEN WHY ARE THEY SO DAMN EXPENSIVE! Steel and aluminum is what, $2/lb? - engine should be under $1000, but a new engine is MUCH MORE.
Assembly i.e. bolting the engine together, probably takes less than 3 man-hours per engine. A lot of that is probably automated. Then testing and packaging and shipping. Another man-hour. This is a guess as figures are impossible to get. Manufactures don't want you to know. So you have to make educated guesses.
But this is irrelevant as the factory gets billed per engine. A material cost.