Photo ou archives : M. Woollett
7813
STUART TURNER
750 Stellar - 1912
From steam to gasoline
The Stuart Turner factory in Henley-on-Thames was the first to produce small steam engines for private launches. In 1912, it staggered the motorcycle world by unveiling a large-displacement two-stroke at the time of the Olympia Motorcycle Show.
Big Ideas
After experimenting with a 300cc two-stroke single intended to power a motorboat, the marque had decided to build a bigger gasoline engine for the motorcycle market.
Tandem Twin
The new machine was powered by a water-cooled tandem twin that drove a two-speed gearbox bolted to its rear, through a 30-plate dry clutch. Gears were shifted by the left hand, while the clutch was operated by the right foot. Final drive was by shaft and endless worm gear, and the machine was started by an automobile-type crank handle carried aboard the machine that engaged with a shaft projecting from the gearbox. The lubrication was not by a gas/ oil mixture like most two-strokes, but oil contained in a compartment in the crankcase was forced out by pressure created by the descending piston and into the upper part of the engine. The prototype (probably the only Stellar ever built) was fitted with a sidecar and used during major military maneuvers in 1913, but no orders were forthcoming, and the project was abandoned when WWI began the following year.
SPECIFICATIONS
Engine: 743cc water-cooled tandem twin
Power Rating: 8 hp @ 1680 rpm
Valves: two-stroke
Fuel System: Senspray carburetor
Transmission: 2-speed, multi-plate dry-clutch; shaft-and-worm final drive
Suspension: Druid laterally-sprung girder forks (front); rigid (rear)
Brakes: cycle-type rim (front); belt rim
Wheels: 3.00x26 inch (front & rear)
Weight: 260 lb
Maximum Speed: 45 mph
Famed for its steam launch engines, the Stuart Turner factory built the Stellar in 1912, but this project for a big two-stroke motorcycle never passed the prototype stage.