Sulzer ZG9 was a pre-World War II opposed-piston two-stroke diesel engine by Sulzer.
[1][2] The engine was available with a choice of two, three and four cylinders (2ZG9, 3ZG9, 4ZG9); the two-cylinder version developed 120 bhp.
It used a piston scavenge pump.
This was mounted vertically above one rocker, driven by a bellcrank from the main rockers.
This engine is sometimes cited as an inspiration for the Commer TS3 design.