A small, scratch-built compressor pump. Allegedly built as a "homer" in one of the great railway works, if everything I buy thus-reputed were as described, it's a miracle there were any locomotives built at all in the last 150 years.
Turns over freely, it's of a size that could be driven by a larger stationary or small traction engine.
Length 6 inches
Height 7 1/2 inches
Flywheel 4 inch diameter