Originally Posted by
ffkiwi
Well this predates the Rossi by a long shot-and the culprit is the 2.5cc FAI limit adopted in the 50s-for both FF and several C/L classes-and it was Europe driven. Bear in mind that Europe (other than the UK) has been metric for a long time so it will be normal to think in terms of mm and cm for cylinder bore and stroke dimensions. Likewise bear in mind that there were already existing 1.5cc and 2.5cc classes in tether car racing [and interestingly this sport STILL has a large following in Europe, despite largely dying out in the rest of the world] so it was merely a case of the FAI ratifying and adopting what were already existing engine sizes-with 2.5cc being the most popular of the small capacity classes. There are only a limited number of 'easy' bore and stroke options that will give you 2.5cc-and engines were already going down the route of 'square' or 'over square' layouts for revs and power-so 15mm bore and 14mm stroke evolved quite early on-and its not as if you can patent the bore and stroke dimensions, so it fairly quickly became the standard European layout for 2.5cc. You may or may not be aware though-that a school of thought held that while 15x14 bore and stroke was good for power, it did not lend itself to the best fuel economy-and a number of TR engines used 14mm bore and 16mm stroke..the Hans Hornlein Taifun Orkan and Webra Mach-II being good examples. Interestingly this was a return to early 1950s 2.5cc bore and stroke measurements-the 14mm bore and 16mm stroke being more common back then-eg the early Webra 2.5s (before the Mach-1....which was an extreme case having a 15.5mm bore and only 13mm stroke)-the Jaguar 2.5, and some of the earlier Hornlein 2.5s
qazimoto is quite correct regarding the Rossi influence-and the subsequent interchangeability of some components from brand to brand as a result (Cox Conquest, Taipan 15 Goldhead being two examples) but the 15x14 layout was established well before the Rossi 15 was even conceived, let alone put into production.
ChrisM
'ffkiwi'
Most of the modern F2A and F2D glow engines have both the Rossi's layout and the 15x14 bore/stroke, as do many of the .15 size buggy motors. The Soviet era Eastern European engines (MVVS etc) are a good source for replacement ABC Rossi 15 p/l. Same with the CS Rossi clones. The cheap Chinese ASP/Magnum .15 glow engines have a p/l that'll fit a Rossi.