Shaft Driven Opposed-Four Motorcycles
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The photograph above of this fascinating motorcycle and the cut-away line drawing of its engine are from Ronald H. Clark's excellent 1964 book, Brough Superior: the Rolls Royce of Motorcycles. (Note: "Brough" rhymes with "tough.") The cylinders in the engine are stacked over each other (see drawing above), unlike in the Honda GL1000, where they are placed fore and aft. Here are some passages about this machine from Clark's book:
like some previous examples,had four cylinders, but there all resemblance finishes for here we have the cylinders arranged after an "H" on its side or, if one prefers it, two horizontally opposed twins one above the other and geared together. Perfect balance was obtained by causing them to rotate in opposite directions but with each pair of pistons (when considered vertically) reciprocating together. George [Brough] called it a "flat vertical"flat for balance, vertical for cooling.
The Brough Superior Dream above is on display at the British National Motorcycle Museum. It was heavily damaged in a museum fire in 2003 that was started by a discarded cigarette. (We owe so much to smokers.)
Brough Superior Dream Engine. Four cylinders: Bore 71mm., Stroke 63mm. -996 c.c. - compression ratio 6.5 to 1. The cylinders are arranged doubly opposed transversely in the frame (one cylinder above the other on each side.) With this arrangement all the cylinders are equally cooled, and the Exhausts, which face forward, give an uninterrupted stream of air cooling them in a manner impossible to achieve with any other arrangement. The cylinders and heads are not shielded from the air by the front mudguard as with other machines. The cylinder block is aluminium carrying liners of special wear-resisting material, and each pair of cylinders (upper and lower) has its own crankshaft. They are coupled together with wide-faced gears, the teeth of which are ground. The crankshafts are each in two parts, the driving side member having the crankpin and driving side journal integral. The main bearings are bronze, and capable of great endurance. The crankshaft arrangement permits the use of bearings of generous proportions, and the connecting rods are of light alloy, operating direct upon the crankpin in accordance with the latest racing practice. There are two camshafts chain-driven to give silent operation, and the cams operate mushroom tappets and have a gradual take-up of tappet clearance to give quiet running. The whole of the valve gear is totally enclosed.
Frame. This is specially designed to accommodate this type of engine, being welded together instead of the usual practice of brazing lugs. This frame also has a fully sprung (plunger) rear wheel which is fitted as standard on other Brough Superior models.
Forks. The Brough Superiorformerly known as the Castletype of fork is fitted as standard on this machine.
General. The remaining specification, such as bulbous-nosed tank and its capacity, saddle height, ground clearance and wheel base, etc., is practically identical to that of standard machines. The Dream could be supplied with 3- or 4-speed transmission, and the final drive is by silent, underslung worm. The rear wheel and all driving mechanism could be detached from the machine in two minutes.
Allan Johnson, whose photos are seen above, adds this postscipt:
In an interview in the early 1960s, George Brough put his decision to not to proceed with the Dream Four as follows, I wanted to go on with the Dream after the war but it was so complex that it would have absorbed all our production facilities. Materials were controlled and one had to undertake to export most of one's production. (These were the requirements of the Labour government of the 1945-1950 period only firms that exported large amounts of their production could get quantities of special steels and other critical materials.)A stash of rare Brough motorcycles, "Broughs of Bodmin Moor," was found in 2015 in Cornwall, England. All were in very bad shape, but their rarity means they are valuable. Included in the stash was the 1938 BS4, a 750cc four-cylinder, shaft drive Brough shown below one of only eight built. It had dual rear wheels and was powered by an Austin engine. It was intended for sidecar use.
More Shaft-Driven Opposed Four Motorcycles!
Brough, the BFG-CitroŽn. and the older Wooler had stacked cylinders on each side. Zundapps and the later Woolers were air cooled with cylinders fore and aft on each side. Honda's famous Gold Wing is liquid cooled, cylinders fore and aft.
Below, on the left is a 1975 Honda GL1000 and on the right is a 1933-1938 Zundapp K800 at the Barber Museum Birmingham, Alabama. The GL1000 and its larger four- and six-cylinder Gold Wing successors have become among the most successful touring motorcycles in the world.
John Wooler started building motorcycles in 1911 and was a designer with many brilliant ideas, but all his creations were unconventional. Rather than conform to the norms, he wanted to do things his way or not at all. After World War II he built a variety of 498cc four cylinder machines with opposing cylinders transversely mounted and shaft final drive. These beautiful OHV machines were built in very small numbers. Wooler died in 1956, putting an end to his exceptional creations.
Allan Johnson sent me the photo below, left, of a 1949 shaft-drive, four-cylinder British Wooler. Allan reports:
Below: The four-cyinder Wooler engine.