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 Dunelt - 250
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Photo ou archives : F-M. Dumas
3817

Capacity : 250
Model :
Production : 1926 - 1928
Category : (R) Street Bike

DUNELT

250cc – 1926

What a top hat entails

Founded in 1913 and out of business in 1956, Dunelt (the name was an abbreviation of DUNford & ELlioT) owed its reputation to its two-stroke singles with the original feature of a double-diameter piston. The lower pan of the piston, with a bigger bore, acted as a pump compressing the mixture in the crankcase, while the "upper floor" of the piston worked in a conventional manner opening and closing the transfer pons.

Tricky to Produce

Ingenious but difficult to produce, the double-diameter cylinder had its little problems. The tall and heavy "top hat" piston de formed when it got hot and had to be assembled with plenty of clearance, which made it difficult to control.

Never a Commercial Success

This problem was never properly solved on the Dunelt 450cc single cylinder, built between 1919 and 1927. The 250 version, which came along in 1925, managed partly to sidestep this handicap, thanks to its smaller piston, and benefited more from the enhanced power output due to this design feature. The 250 reached more than 70 mph on the racetrack ridden by – among others – Ewald Kluge, the famous German ace who would demonstrate his talents with another leading light of the two-stroke world: DKW. Though it achieved fame with the success of its curious power plant, Dunelt never made a commercial success. From 1928, Dunelt abandoned the top hat two-stroke for conventional four-stroke units of 250, 350, 500 and 600cc.

SPECIFICATIONS

Engine: 248cc (68x68mm) air-cooled single-cylinder; double-diameter pumping-piston

Power Rating: 8.5 hp

Valves: two-stroke

Fuel System: Amac carburetor

Transmission: Sturmey-Archer 3-speed handshift, chain final drive

Suspension: girder forks (front) ; rigid (rear)

Brakes: drum (front & rear)

Wheels: 19 inch wire (front & rear)

Weight: 198 lb

Maximum Speed: 65 mph

The little Dunelt looked conventional enough, the double-diameter "top hat” piston that acted as a supercharging pump.






Le fichier Moto Passion réalisé par François-Marie Dumas réunit près de deux mille photos accompagnées d'un historique très complet des machines présentées.
Il sera progressivement mis à jour ici et toute information complémentaire est la bienvenue sur info@moto-collection.org.

Cette documentation unique, qui constitue sans doute l'encyclopédie la plus exhaustive jamais écrite sur l'histoire de la moto, a été réalisée avec l'assistance de nombreux spécialistes dont principalement Didier Ganneau, Christophe Gaime, Mick Woollett, Jean Goyard, Bernard Salvat, Christian Rey, Yves Campion, Helmut Krackowizer, Michael Dregni, Michel Montange, etc. que je remercie ici.

Disponible sur demande :
- Les fiches originales sur papier
- Les photos et archives signées de mon nom en haute définition ou les documents originaux.
Me contacter sur info@moto-collection.org pour les conditions et droits d'utilisation.