A Unique Briggs and Stratton Model FH Conversion

A modified Briggs & Stratton Model FH is still enjoying the show circuit as a hit-or-miss engine under its new owner.

| April/May 2019

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B&S Model FH Conversion

Builder: Gary Richardson, Buna, TX (originally Briggs & Stratton Corp., Milwaukee, WI)
Year: Circa 1928 (FH production ran 1925-1933; slant fin FHs were early production engines)
Serial No.: N/A
Horsepower: 1/2hp @ 1,800rpm
Bore & stroke: 2-1/4in x 2-1/4in
Flywheel: 9-1/2in x 1-1/4in
Ignition: Spark plug with battery and coil
Governing: Hit-and-miss with flyball governor (originally throttle-governed)
Cooling: Air


People express themselves in a wide variety of ways. Some paint pictures, some compose music, others build houses, while yet others craft fine jewelry. A few, like Gary Richardson, retrofit old engines, converting them into hit-or-miss engines.

The speed of many small, 4-cycle engines is governed by the throttle opening. Weights are mounted within the flywheel, and as the flywheel rotates, centrifugal force moves the weights outwards, in turn working the butterfly valve in the carburetor to maintain the desired speed of the engine. In earlier hit-and-miss engines, an external flyball governor connects to the exhaust valve via linkage. When the speed of the engine is below a given level, the exhaust valve operates as normal, staying closed on the intake stroke as the piston draws down, creating a vacuum that opens the intake valve for the admission of the fuel/air mixture, which is then ignited (the “hit”) to produce a power stroke.



flyball-governor
Front view of the engine showing valve gear and flyball governor.

When the speed exceeds the desired level, the governor holds the exhaust valve open. With no vacuum in the cylinder, the intake valve stays closed and there is no admission of fuel/air (the “miss”). As a result, hit-or-miss engines have a distinctive sound when running – “bang, whoosh, whoosh, whoosh, whoosh, bang, whoosh, whoosh, whoosh, whoosh.” One or two heavy flywheels serve to maintain a more-or-less constant speed.



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