"This motorcycle is old but good."
Translation:Dieses Motorrad ist alt, aber gut.
Maybe there are some inconsistent relics. But usually Duo is quite consistent here. Note that there are discrepancies between the attributive (in front of a noun phrase) and the predicative (standalone) position.
In the attributive position you need to be strict and translate "this" as "dies(xxx)". But standalone it could be (and frequently is) "das" as well.