That is why they have to be careful, the introduction of a model in 1997 does not exclude it from having patents to its engine and since it is only 14 years old it could legitimately have patented engine components. Only an exact copy of a 1992 or earlier year model can be manufactured with out possibility of patent infringement.

However if no patent is filled or offered, then there is no restrictions other then those of a trademark or copyright on the brand name. They cannot say it is a copy of a Kawasaki engine, for example.