Not a lot is know about the Hesse Hornet air compressors. They used a Kaiser Industrial Engine Model CJ-3A mounted on a steel chassis. The number 1 & 4 fired cylinders were normal, while the number 2 & 3 cylinders were used to compress the air . The blocks are late model CJ-3A and use a heavier fly wheel to make up for having to fire on just two cylinders. The idle speed was also increased from 600 to 850 RPM. If you have more info or photos, please contact me.
Benjamin Griffiths sent in these two pics of the compressor head: