The Otto patent specified 4 strokes- so designers attempted to design engines outside the patent. Samuel Griffin designed the six-stroke engine in 1883.
Induction
Compression
Ignition
Partial exhaust
Air blast
Complete exhaust
That was 2 strokes doing nothing- to get around the patent
In 1898 Dick Kerr of Kilmarnock bought a Griffin patent to build a six stroke engine- two were made as Ottos patent lapsed in 1890.
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