"John Deere-designed and -manufactured diesel engines provide excellent torque, fuel efficiency, and durability." - straight from John Deere's website. Really not that hard to find out. On the smaller series, John Deere post the fact that they are powered by Yanmar right there on the tractor's page. It isn't some big, shameful secret.
I was just curious, given the history of 5,000 series.
Say, the previous 5420 and 5510 made by Kukje.
Not really "smaller" than the 5 series being touted here.
As I remember it, not that much publicized as "Korean" or "Asian" tractors in the early 200x years.