Classic Machines TractorsClassic Machines: The Allis-Chalmers HD-21 tractorCharles FairbairnMarch 23, 2016July 17, 2018 by Charles FairbairnMarch 23, 2016July 17, 2018 Developed directly from their model HD-20 (introduced 1951), the HD-21 featured among other things, one of the diesel engines from the recently acquired Buda Engine
