Sunbeam S7 500, S7500De Luxe

Sunbeam S7 500, S7500De Luxe
Manufacturer	Sunbeam
Production	7 658 units (inc. De Luxe models)
Engine	Parallel twin, SOHC
Compression ratio	6.5:1
Top Speed	121 km/h / 75 mph
Transmission	4-Speed
Frame	Twin cradle, steel
Suspension	Front: Telescopic, one way damped Rear: Plunger, spring loaded saddle
Brakes	Front: Drum, leading shoe, 203 mm / 8" Rear: Drum, leading shoe, 203 mm / 8"
Wheelbase	1400 mm / 57"
Weight	195 kg / 430 lbs (dry),
Manuals	Service Manual

It could reach a top speed of 121 km/h / 75 mph.

Engine

The engine was a Air/Oil cooled cooled Parallel twin, SOHC. The engine featured a 6.5:1 compression ratio.

Drive

Power was moderated via the Single plate, dry.

Chassis

Stopping was achieved via Drum, leading shoe, 203 mm / 8" in the front and a Drum, leading shoe, 203 mm / 8" in the rear. The front suspension was a Telescopic, one way damped while the rear was equipped with a Plunger, spring loaded saddle. The bike weighed just 195 kg / 430 lbs. The wheelbase was 1400 mm / 57" long.

Photos

Overview

Sunbeam S7 500

WHEN THE 1946 SUNBEAM S7 was unveiled to the post-war biking public, it was one of the most technically advanced motorcycles of its age. With its all-aluminum, "unit-construction", single overhead-camshaft, horizontally split engine, it also boasted shaft drive, a smooth power delivery and numerous other technical refinements that ensured it was going to be a massive hit. Or so felt BSA which had acquired Sunbeam in 1943.

In fact, the bike turned out to be something of a sales flop and was (arguably) one of the most woefully under-supported acts in the history of British motorcycling. It could have been great. But instead, it was merely adequate. Other problems with the S7 prototypes included stripping of the underslung worm gear final-drive—that in turn is said to have led to swingeing cuts in engine power, the concomitant of which was a fairly mediocre (and struggling) 75-mph performer in an age when riders were pushing hard for the magic ton. However, according to David Holyoake of Sunbeam specialist Stewart Engineering, there was never anything wrong with the worm final drive which, over five decades, has proved to be very reliable in service and maintenance light; a claim borne out by the direct testimony of many other Sunbeam S7 and S8 owners who have had no trouble whatsoever in tens of thousand of miles. However, the correct AG140 oil is crucial. Meanwhile, oil capacity for the wet-sump engine was, at just three pints, always marginal leading to overheating with the very real risk of engine casting distortion and/or seizure (an aftermarket extended oil sump is available from Stewarts and is advised). But the handling, with its one-way damped telescopic front fork (no damping on early models), plunger rear suspension and 16-inch balloon tires, left much to be desired. And words such as ‘wallow’ and ‘weave’ were, with some justification, quickly associated with the mount. Meanwhile, the 8-inch single leading shoe brakes, although not bad for the performance, would never be described as particularly impressive. Moreover, a bulky machine like this was always likely to find both an ally, and an enemy, in ordinary wind resistance.

Make Model.	Sunbeam S7 500, S7 500 De Luxe
Year	1946 - 56
Production	7 658 units (inc. De Luxe models)
Engine Type	Parallel twin, SOHC
Displacement	487 cc / 29.7 cu in
Bore X Stroke	70 x 63.5 mm
Compression	6.5:1
Cooling System	Air/Oil cooled
Lubrication	Wet sump
Starting	Kick
Electrical System	6V
Max Power	18.6 kW / 25 hp @ 5800 rpm
Clutch	Single plate, dry
Transmission	4-Speed
Final Drive	Shaft
Frame	Twin cradle, steel
Front Suspension	Telescopic, one way damped
Rear Suspension	Plunger, spring loaded saddle
Front Brakes	Drum, leading shoe, 203 mm / 8"
Rear Brakes	Drum, leading shoe, 203 mm / 8"
Wheel, Front	4.50 x 16"
Wheel, Rear	4.75 x 16"
Wheelbase	1400 mm / 57"
Dry Weight	195 kg / 430 lbs
Top Speed	121 km/h / 75 mph
Source	Sump Publishing

External Links

• http://www.sump-publishing.co.uk