‘Is $650 too much to pay for a 2-1/2 HP Hercules Model SK
engine?’ That was the way a conversation started with Rex Pyles
at the recent gas engine show in Portland, Ind. My reply was to the
effect that you probably won’t have another chance to get one,
because I have only seen one other. About a half an hour later, Rex
came by again and said he was able to get it for $600. He brought
it by later on his way over to his exhibit trailer. It is engine
number 369868, manufactured in 1928.
The normal 2-1/2 HP Model S is unique in a couple of ways.
First, it is a departure from the normal Hercules engine design in
that the valves are side by side, rather than above and below, in
the head. To accommodate this valve arrangement, the rocker arm is
set at a slant. The crankcase area has no cast bottom and the fuel
spout comes either out of the front or rear of the base.
Secondly, the 2-1/2 HP Model SK is unique because it is a
throttling governed kerosene engine, yet it still has the open
crankcase and spoke flywheel design. The 2-1/2 HP Model SK and the
smaller 1-3/4 HP SK were in production in 1928 and 1929.
Interestingly, when Hercules offered these engines they also
offered the newer three-hole flywheel Model XK throttling-governed
engines in 1-3/4, 2-1/2 and 3-1/2 HP sizes. Sears only offered the
XK models at this time.
The governor mechanism was modified, with an arm going into a
hole in the side of the block with a rod to the throttle butterfly
running along and on top of the fuel tank and coming out a hole in
the front of the base. Most of the later engines of these sizes had
the governor arm hole cast into the base, even though the vast
majority of the S models at this time were still hit-and-miss
The production run on the 2-1/2 HP SK Hercules lasted about a
year and a half. I would guess fewer than 300 were ever built.
Glenn Karch is a noted authority on Hercules engines. Contact
him at: 20601 Old State Rd., Haubstadt, IN 47639, or e-mail