Although the precise details of their history are rather obscured by an almost complete lack of documentary evidence in the English language, the TOP range of model engines produced in Osaka, Japan during the early post-war period represented a technically interesting and well-executed attempt by its manufacturers to become established in the highly competitive post-war model engine marketplace. The earliest models such as the illustrated TOP 19 featured a piston port transfer arrangement like that seen on the M&M and Super Atom models from America. Later models such as the TOP A and TOP 33 models reverted to more conventional porting arrangements. The range included multiple variants of piston port designs in both .19 and .23 cuin. displacements as well as the later TOP A and TOP 33 glow-plug models.
The complete story of the TOP range range may be found on Ron Chernich's "Model Engine News" (MEN) web-site.