Aspin and Company Ltd. had a feature that can be considered brilliant, which was their rotary valve system in the cylinder head. In fact, the whole combustion chamber was rotating uncovering different intake and exhaust ports.

-They had 4 horizontally opposed cylinders, and at least there were three versions. In 1937, the 80 hp engine came out with 5,000 rpm.

"Aspin 4-cylinder boxer engine"

-The first model had the rods of each opposite cylinder moving in the same direction. Between 1938 and 1941 this was changed, and they moved in opposite directions for equilibration.

"Aspin valve"

-We have a better look at the combustion chamber, whose rotating "head-valve" is driven by gears instead of traditional rockers. This conical valve has holes that match the intake and exhaust ports in the cylinder head itself.

-We can see this in the figure below with the cover removed. We see the two gears that make the two chambers turn synchronized.

"Aspin, details"

-Below we see a cross-section of the engine base with more details.

"Cross-section Aspin"

-In 1938, Briggs Manufacturing Corp. in Detroit, MI. acquired the rights to manufacture it, but we do not know their progress in this new venture. It seems that WWII interrupted its development there. In the UK, between 1944 and 1946, it reached 110 hp at 2500 rpm and 114 hp at 2800 rpm with more displacement.