pony engine

Noun

 * 1)  A small locomotive used for shunting wagons, etc.
 * 2)   A small gasoline engine serving as an auxiliary to a diesel engine (mainly in older designs from the 1930s to 1950s), providing heat to warm it up and, when engaged with a clutch, providing cranking to start it up.
 * 1)   A small gasoline engine serving as an auxiliary to a diesel engine (mainly in older designs from the 1930s to 1950s), providing heat to warm it up and, when engaged with a clutch, providing cranking to start it up.