A little something what I wrote for 'Yowl', the official organ of the Scott owners club, and which might also be of some interest here:-
As the stationary engine collecting son of a Scott motorcycle enthusiast, I have always sought to add examples of the marque to my collection and was recently lucky enough to acquire one of the 'PA' types which were used to power the wartime Bofors anti-aircraft gun. At first sight one might doubt that this was a Scott design at all - it is after all air cooled, petroil lubricated and has a flat (well, slightly conical) piston crown. However, the connecting rod has that familiar thin oval section and the 'style' of the main castings with their various cover plates is somehow reminiscent of the three cylinder motorcycle engines. But what of that flat top piston - surely loop scavenging was an entirely alien concept to Scott until the much later Swift project?
Investigation of the cylinder porting revealed it was indeed a loop scavenged design, with not only classic paired Schneurle type transfer ports at approximately 90 degrees to the exhaust port, but also a small 'boost' port at 180 degrees (i.e. opposite the exhaust). This arrangement is widely supposed to have made its debut in 1957 on Walter Kaaden's successful 125cc MZ racing machines (e.g. Cesare Bossaglia 'Two-Stroke High Performance Engine Design & Tuning' and Graham Bell 'Two-Stroke Performance Tuning'), though the typically thorough Phil Irving ('Two-Stroke Power Units') points out that a similar system was patented by Zundapp in 1933, primarily in an attempt to circumvent the Schneurle patents, but not pursued for production until much later. Whatever its precise origins, the appearance of such a boost port in a production engine of the 1940's can be considered pretty 'cutting edge'.
Some digging on the internet turned up GB patent number 512980 'Improvements in or relating to the scavenging of the cylinders of two-stroke-cycle internal combustion engines' granted to Scott Motors Saltaire Ltd. and William Cull in 1939 and describing precisely this arrangement of ports. Interestingly the design is illustrated on an engine bearing a distinct resemblance to the Cyc-Auto (it has the characteristic inlet passage running down the side of the cylinder from a high mounted carb). I'm not sufficiently familiar with the various Cyc-Auto engines to be able to say whether the third transfer port was used on production models - but if it was, then that least regarded of Scotts may just be one of the most technically advanced!
(link to patent -
Nick H