Hirth Motorcycles

Hellmuth Hirth b.1886, Albert Hirth b.1858, Wolf Hirth b.1900

Built by pioneer aviators Hellmuth and Wolf Hirth in Stuttgart, 1923~1925. The motorcycles were very highly regarded and achieved excellent results in competition. Wolfram lost his leg in a 1925 racing accident but this seems to not have slowed him down as he was still setting records in 1926. The Hirth firm was founded in 1920 as a manufacturer of aircraft engines, and in 1927 part of the company was divided off to become Mahle of piston fame.
The younger of the two brothers, Wolfram was a founder of the Schemp-Hirth glider company, and flew sailplanes wearing a prosthetic limb. The story has it that he had one of the smaller bones from his amputated leg fashioned into a cigarette holder.
The Hirth, Schemp-Hirth [1] and Mahle companies all remain operational (2019).

Engine & Pistons Deutsche

The goal was the development of solid pistons made of "electron", an aluminum-magnesium alloy. This metal was lighter than the aluminum-copper alloy currrently in use, and thus suitable for increased engine speeds.

The most economical method of development was to use small engines - inexpensive experimental motorcycles. So Hirth's two-wheelers acted primarily as a test-bed for the new material.

Common to all machines from the Hirth workshop were two-stroke engines with double pistons. Sometimes with two, then with four pistons. The motorcycles from the Cannstatter experimental building all had water cooling, and the two connecting rods of each cylinder ran side by side on a common crankshaft crankpin. The combustion chamber in the cylinder head had a central spark plug.

Successful riders of the "Hirth" racing machines
· Wolf Hirth
· Erwin Gehrung
· Franz Islinger

Hirth-Verzahnung

The Hirth coupling (or Hirth joint) was developed by Albert Hirth, the elder of the three brothers, for use in aviation engines. It has a great many applications and was used, for example, in the Adler twins of the 1950s. The Hirth-Verzahnung is currently in use in aviation turbine engines, surgical operating equipment, bicycle cranks and photography gear (rosette).

Technical data, Hirth racing motorcycle (#120)

Deutsche

Water-cooled single-cylinder two-stroke double-piston engine with horizontal cylinder.
Bore 45 mm, stroke 80 mm.
Displacement 254 cm³, approx 11 to 14 hp at 8000 rpm, three-speed Burman gearbox, chain drive.
Chassis: twin loop tubular frame with brazed fittings,
Webb fork, rigid rear, Simplex half-hub drum brakes, front Ø 120 mm, rear Ø 150 mm
Weight approx. 80 kg
Tank capacity 15 litres

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Notes 1. Shemp-Hirth gliders have won more world championship events than any other brand - in fact, more than all the other brands combined. World records include a soaring flight in the Andes of over 3000 km by Klaus Ohlmann, who has also soared over Mount Everest.

Sources: François-Marie Dumas, Wikipedia, Zweirad Museum, schempp-hirth.com

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