The first IHC "Highwheeler" truck had a very simple
air-cooled horizontally opposed two-cylinder engine with a stroke and a bore, and produced around .
Displacement was . In 1915 a new
L-head water-cooled inline-four engine appeared. While International's own engines underwent constant developments, the pace of truck production in the twenties was such that others' engines (from
Waukesha,
Buda, and
Lycoming for instance) had to be installed in some parts of the range. International Harvester's first in house six-cylinder engines appeared in some of the 1926 S-series trucks, seemingly a response to market pressures rather than to any particular need for such a layout. In 1928, a new heavy range of trucks (the HS-series) built around a series of engines from
Hall-Scott appeared. These engines were used by IHC for some heavy-duty applications until 1935, although their own large engines ( FBD and FEB) had appeared in 1932. The medium-duty 1930 A-series trucks received the all-new FB-3 six-cylinder engine, with
overhead valves and seven
main bearings. This was complemented by larger versions of the same engine and was built until late 1940 (as the FBB), the line-up being expanded downward by the smaller FA-series (later FAB) in 1933. The HD
inline-sixes, later to become the first in International's long running "Diamond" series, first appeared in the C-30 truck of 1934. Available in three different displacements (see table), they were renamed "Green Diamond" in late 1940 for the 1941 model year after a number of detail improvements. ==International Harvester/Navistar engines==