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Ariel Leader Four Prototype

Make Model	Ariel Leader 4 Prototype
Year	1962
Production	Never reached full production
Engine	Four stroke, four horisontal cylinders on the left with in-line crankshaft, OHV
Capacity	696 cc / 42.5 cu in
Cooling System	Air cooled
Lubrication	Wet sump
Exhaust	4-into-1
Induction	Single Zenith carburetor
Ignition	Coil
Starting	Electric
Max Power	18.6 kW / 25 hp
Clutch	Morris Minor car clutch, syncro-mesh gearbox
Transmission	4-Speed
Final Drive	Shaft
Frame	Pressed steel frame with leg shields
Wheels	Steel, laced wire spokes
Front Rim	3.25 x 17
Rear Rim	4.00 x 16
Front Brakes	Drum
Rear Brakes	Drum
Wheelbase	1448 mm / 57 in
Source	National Motorcycle Museum, UK

This fascinating 700cc prototype, tested at Ariel circa 1960, shows that BMW’s four-cylinder K100 was not exactly original when unveiled in 1983.

The prophetic Ariel looks similar to the company’s innovative 250cc Leader two-stroke launched in 1958, with a pressed-steel frame, leg shields and windscreen. But the power unit is unlike anything else from a British factory. The crankshaft is set in-line with the frame and slightly offset to the right, with four horizontal cylinders on the left. Final drive is by shaft, via a four-speed gearbox is built in unit with the engine. Cooling of the exhaust port area is fan-assisted and oil is carried in a wet sump.

Found to be comfortable, tractable and extremely quiet, the luxury electric-start Leader 4 was not fast. In prototype form, the single carburetor engine designed by industry veteran Val Page produced no more than 25bhp. Ariel engineers believed their design had potential, but the parent BSA Group saw no future for it in the age of the BMC Mini car and cancelled the project.