Barr and Stroud Sleeve Valve Four Stroke Engine.

 

 Barr & Stroud were the first British company to build sleeve valve engines for non-vehicle application, based on the Burt McCallum patent. The valve was designed to rotate and reciprocate between the piston and the cylinder barrel. Sleeve valve engines held an advantage over poppet valves in the early years but the reciprocating mass restricted engine speed to about 3000 rpm.
The company began production of this engine just after WW1 as a stopgap measure when demand slowed for their regular business of telescope and optical equipment. As this business returned to normal, engine production tailed off and by 1926 had ceased completely.