Sunbeam Model 6

   

Make Model.

Sunbeam Model 6 "Lion"

Year

1921 - 37

Engine

Single cylinder, side valve

Capacity

492 cc / 30.0 cu in
Bore x Stroke 77 x 105.5 mm
Cooling System Air cooled
Compression Ratio 5.0:1
Exhaust Single

Starting

Kick
Power 3.4 kW / 4.5 hp
Transmission 3-Speed wide ratio
Final Drive Chain 
Gear Ratios 1st 13.7 / 2nd 8.2 / 3rd 4.9:1 (Side car model: 1st 14.6 / 2nd 8.7 / 3rd 5.25:1 or 15.5, 9.3 and 5.6)
Frame Single downtube cradle

Front Suspension

Druid forks

Rear Suspension

Rigid, spring loaded saddle

Front Brakes

Drum

Rear Brakes

Drum
Wheels Steel, laced wire spokes
Tyres, Front and Rear 3.25 x 26" (Optional: 3.50 x 26")
Dimensions Length:  2083 mm / 82"
Width       813 mm / 32"
Wheelbase 1359 mm / 53.5"
Saddle Height 711 mm / 28"
Dry Weight 136 kg / 300 lbs
Fuel Capacity 11.4 L / 2.5 Imp gal / 3.0 US gal
Oil Capacity 2.3 L / 4.0 Imp pt / 4.8 US pt
Source Sunbeamsidevalve.com
   

The 1921 French Grand Prix proved a successful testing ground for Marston's prototype, long-stroked engine of 492cc.  It had a 77mm bore by 105.5 mm stroke. The 'Longstroke' model went into production the following year, winning the Senior T.T. It was the last side-valve engined motorcycle to do so.

The Sunbeam Longstroke was the fastest production, single cylinder, side-valve motorcycle in its day. The model stayed in production for the life of the company and the subsequent AMC take-over in late 1937. It underwent many stylistic changes; notably from flat tank to saddle tank in 1929. Known as the Model 6 prior to ICI's takeover of the company in 1929, it was marketed as 'the Lion' during the 1930s - the tank emblazoned with ICI's trademark lion emblem.