managed after very many years to get hold of a copy of that wonderful book by Philip H Smith " The High Speed two-stroke petrol engine" . As a young man I was enthralled by it when borrowed from my local library and since many of my generation started out on two strokes I am certain others retain a soft spot for them. This page above illustrates a range of piston crowns and for good measure Smith included a Manx Norton one on the bottom right corner. 

 

 

 

I was significantly lighter in my younger days and so the scale of those lightweight machines was an added attraction. The popularity of the disc intake valve provided the answer to a lot of the issues of timing racers using the two stroke principle. What a pity that emission laws have all but made them disappear. There is certainly a need to redevelop the two-stroke in harmony with current emission thinking and technology.