They probably are, but the human body is incredibly resilient when it comes to heavy loads, if you train for it.

Notice that he is standing upright, with the weight of these engines pulling down on his shoulders and spine, maximizing the absorption of the energy by his body and allowing him to keep walking

As for the actual weight here, it highly depends on what kind of engines these are. Small engine blocks can be as light as 44lbs each (totalling here 132 pounds) or as heavy as 600 or more each.

But these don’t look like massive truck engines, so let’s say they’re about 100 pounds each. That is easily doable for someone who is used to the weight.