Here is the thing the parts that are mechanical may or may not have enduring market value, engines in many cases become outdated and in that they loose functionality as in they can become functionally obsolete. However what is a relatively new and unique design is typically protected for a set time and then afte rthat set time expires it then enters what is called the public domain and then any can manufacture it. This is good since the inventor can recover the research and development costs. It is also good if it is an enduring design and with a long term of functionality, then everyone can get access to that design and society is not deprived of access to the technology.


However as for the appearance and looks of an object that can be timeless and in that the right to retain the exclusive rights to the design is the choice of the designer. They can retain their rights indefinitely.


If the appearance is not important and does not have material value….then why copy it? The copying and subsequent sales are damages to the original designer, they are recoverable and without time limits in many countries.