Make the Sunbeam motorcycle a market winner

Looking here it seems the worm drive wasn't as bad as often reported. http://classicglory.co.uk/models.htm

However, to run a higher power engine a change to BMW-like spline geared shaft drive is a smart move. What else should we change for the 1946 launch of the Sunbeam S7, setting the marque for a successful S7 Deluxe and S8 in 1949?

Keep in mind the technological, and manufacturing limitations (including industrial relations) of late 1940s Britain (and Sunbeam's BSA ownership) and the markets needs and preferences of the time. For example, is a change to swing arm from plunger suspension likely?

If the target market is redefined as the North American interstate rider then a move to a 900cc twin wouldn't be ASB territory. The crankcase breather and other oil leak sources would need addressing.

Imo, BSA lost an opportunity to bring innovation to this sector with the S7. Let's try to make it right.
 
The worm drive components are below. Swapping this out for bevel drive shouldn't be a technological stretch.

WormWheel2.jpg
 
Positive earthing (using the bodywork or chassis) promotes corrosion. Negative earthing prevents it to some extent.

Positive earthing is a bad idea to start with, but it's even worse when dealing with the build quality of British motor vehicles in the 1960s-1980s.
 
Negative grounding promotes corrosion in wiring and connectors, what I call green death. It's one other side of the negative/positive ground question. High quality wiring and connectors minimize the effects. The catch is that "high quality" part. Another side is that negative ground was quite standard in the target American market, a reason to switch. Another reason is that the advent of electronics spelled the doom for positive ground.

Apart from a poorly engineered drive shaft with poor quality materials, what other qualities did the Sunbeam S-7 possess? By this time, the Sunbeam name was just another corporate name, borne on a fairly lack-luster motorcycle with mediocre performance and an Achilles heel shaft drive. Jeez, who wouldn't want to own and ride something like that? It would take a special person to turn this sow's ear into something desirable. Corporate boards aren't special persons, usually.
 
A reliable, higher hp S-7/8 would offer the convenience of shaft drive, good all weather use due to deep fenders and wider tires, the compactness of an engine inline with the frame. Outside of the engine layout the above rings true also for the BMW R 12 from the late 1940s.

bmwr512c.jpg


9638275_orig.jpg


Fix these problems, and the sunbeam should be able to exploit the same market as the BMW airhead.

but in the end I must admit, I just like unique look.

 
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Nothing wrong with a shaft drive parallel twin, but mount the engine transversely (the cylinders aligned across the frame), for better cooling, to eliminate having a back cylinder, that runs hot, due to air flow being blocked by the front cylinder. If Sunbeam insists upon keeping the engine an inline twin (say they want it to be their trademark, like the boxer twin is for BMW), then do like Triumph did with the present day Rocket 3, liquid cool the engine.
 
I like the look of the Nimbus and Henderson/Indian Four. How did they manage to cool the rear three pots? Can the Sunbeam learn anything from these?

1927_Henderson_Four.jpg


Henderson-1931-KJ-10.jpg


mc-img-51.jpg
 
The lesson learned is that with more power comes more heat. The simple answer is less power. More responses came in the aviation field with ducts and deflectors, such as James Baker's solution to the Napier Dagger's dilemma of how to cool an air-cooled V-12.
 
I like the look of the Nimbus and Henderson/Indian Four. How did they manage to cool the rear three pots? Can the Sunbeam learn anything from these?

1927_Henderson_Four.jpg


Henderson-1931-KJ-10.jpg


mc-img-51.jpg


They both ran hot on the back 3 cylinders (as did the Ariel Square 4). The saving grace of the Nimbus and Henderson/Indian 4s, is that for their size, they were relatively low performance engines (for being a 1200 cc engine, the Indian 4, was hard pressed to do 100 mph), which helped to keep engine temperatures from going even higher than they did. To have half a chance at cooling the engine decently, you'd have to do like Continental, and Lycoming do on their opposed 4, and 6 cylinder air cooled aircraft engines, and run baffling around the cylinders, to guide additional cooling air, to the cylinders behind the front cylinder(s).
 
Pre-ww2 Scott motorcycles had liquid cooled 3-stroke motors, but without water pumps. Perhaps water cooling for the Sunbeam isn't a technological or costly stretch.
I wouldn't normally argue, but the Scott was only 2-stroke, not 3, and water-cooled pre-WWII. The Silk version, built much later, was liquid-cooled, and too expensive, but what a machine. I have a soft spot, particularly for the sound, the banshee wail of the Scott Flying Squirrel racing down Glencrutchery. BSA wasn't willing to install high-quality switches and levers when they installed a BSA front end. I'm sure the BSA bean-counters would give a banshee wail when they found out what liquid cooling would have cost.
 
I wouldn't normally argue, but the Scott was only 2-stroke, not 3, and water-cooled pre-WWII.
Correct on 2 stroke, my typo there. Water-cooled is liquid cooled in my book. But what caught my attention was the lack of water pump, presumably for simplicity sake. The Sunbeam could perhaps do the same.
 
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