Originally Posted by
Mr Cox
Many glow engines are the same, or close to it. I guess it is a nice round number for a slightly over square .15 engine (15.0mm bore and 14.0mm stroke).
The Rossi .15 glow came out in the late '60's and I believe that it's generally considered to have had the greatest influence on the design of high performance 2.5cc glow engines ever since. It had the 15mm bore 14mm stroke. Since then most similar engines have shared the dimensions because of Mr Cox's reason above. Very often a Rossi .15 p/l will be a drop in fit into a later engine of another brand.