Sleeve valve engines
As the name implies, sleeve valve engines do not have conventional pushrod operated valves. The piston moves within a sleeve which has inlet and exhaust ports cut through the wall. The sleeve in turn moves within the cylinder outer casing, by means of a bell-crank to open and close the ports as required, i.e. opens to the inlet manifold to allow the flow of fuel/air mixture into the cylinder via the corresponding opening on the cylinder barrel and opens the exhaust port to the corresponding opening in the cylinder barrel to allow the combusted gas to flow to the exhaust stub. The cylinder head, known as the junk head, houses the spark plugs. So what you have is a piston moving within a sleeve which moves within the cylinder barrel. Sleeve valve engines are generally very reliable and deliver good power to weight ratios. They, like any radial engine, do emit copious clouds of oil smoke on start up. This is why ignition is not introduced until the oil is scavenged from the lower cylinders on start-up on radial engines and the sleeve-valve engine in particular used a good quantity of oil in normal operation due to the need for additional lubrication as compared to a conventional OHV engine, three to four gallons per hour not being uncommon, although they also usually leaked plenty too in my experience with them on Bristol Freighters.