Silk 700S

[Radar]

Silk 700S Mk2

The grandad of the YPVS!

From elsewhere on the web:

I’m not sure when I began looking for a Silk. Only 138 were produced from 1975 through 1979. I had raced against one in New England in the late 70’s, but never saw another. I first saw the listing in some obscure corner of the internet, late at night, in the dead of winter, 2003. After 12 months of unpleasant haggling, I had made a deal at 40% above the original asking price. It’s easy to see why I don’t enjoy negotiating.
Of course, there is always a risk buying sight unseen, and an additional risk with a motor that has been dormant for decades. While the Silk was relatively easy to get running, a transmission defect immediately became apparent: it was jumping out of second gear. Maybe that was the reason it became dormant. Some research and patience soon had things sorted, and I began sifting through other minor problems.

George Silk took his passion for antique Scott motorcycles (as in Scott Flying Squirrel) and translated it into a simple yet effective motorcycle for the new era. Maybe George was ahead of his time, under-funded, or both, because his venture turned out to be commercially unviable. The motorcycle, however, was definitely viable, and Mr. Silk’s efforts to modernize a design from the 1930’s were, in fact, successful.

The 700cc 2 stroke twin is water cooled, with a prominent radiator in the conventional location. Unusually, there is no water pump, instead a large header tank above the radiator sets up a thermo-siphon effect that circulates coolant as needed. The automatic oil injection system uses a very robust aviation pump fed by a huge reservoir under the seat, good for nearly 1000 miles. The Silk evolved the Scott’s deflector top piston design, making it more compact, with advanced gas flow technology and port configuration, a 2 into 1 exhaust system, a single carb intake manifold design, and electronic ignition. The result is a power band a mile and a half wide. This big stroker pulls from under 2000 RPM to its 7000 RPM max, more like a big 4 stroke single.

The wide power band is no luxury, for the transmission, borrowed from a Velocette Venom, has only 4 speeds, and they‘re spaced wide apart. The gearing overall is rather tall, in the British fashion, so some slipping of the high lever effort clutch is required to get underway. With a perfect, gentlemanly, sporting British riding position: narrow sport bars with mildly rear-set footrests, one immediately feels at home on the machine, and the seat is plush.

At only 310 pounds, even the mere 45 horsepower that the mildly tuned, lightly stressed engine produces is adequate to maintain a respectable pace. The Spondon frame is an enlarged derivative of a 125cc road race frame, and features straight connections between the steering head and swing arm pivot, which is eccentrically mounted to allow for positively precise chain adjustment. Combine this with Girling shocks, Cerriani style forks, alloy rims, stainless steel spokes, Lockheed brakes and a gorgeous alloy 5 gallon fuel tank, and you have the quintessential British handling package.

The ride is….different, and pleasant above all. The long stroke 180 degree twin growls like an outboard on steroids, building power as the revs rise. Vibration is noticed as a buzz at higher RPM’s but the tall gearing insures that cruising speeds lie well below this range. The brakes are not overly sensitive, but cope easily with this lightweight. The steering and road-holding are remarkable, as only a 310 pound motorcycle can be. The skinny tires accentuate the airy feeling of lightness. Corners can be attacked and strafed with wild abandon, but do be careful. You wouldn’t want to wad up this much history.

https://www.retrotours.com/bikes/1977_Silk700s_SabreMK2.html

[Lex]

Utter Junk, got what it deserved. Jap bikes at the time were way better

[Radar]

Silk 700S

The Silk 700 was one man’s lifelong ambition; to revive the glory that was once Scott motorcycles.

Alfred Angus Scott was a Victorian visionary who almost single-handedly invented the large capacity two stroke motorcycle, then went off to do something odd with sidecars.

Some 60 years later, George Silk took the canted forwards, deflector piston, water cooled, two stroke engine concept and applied it to the 1970s touring market. It almost worked, but rocketing petrol prices and new emissions laws pulled the plug on the high quality Silk 700 before it got going. Great idea, wrong decade.

Long ago, bikes were manufactured in the North of England. Marques like Phelan & Moore made Panthers in Cleckheaton, Dot were in Manchester, Scott´s smoked out of Shipley . This is the story of last roadgoing big capacity two stroke manufactured in England; Silk of Derbyshire.

Like many stories from the pioneer days of motorcycling, this is all about one man´s vision; a dream of taking on the world´s best manufacturers with a truly unique design. It was remarkable that even as the mainstream British bike makers like Norton and Triumph were sliding into bankruptcy during the 1970s, a small band of craftsmen were still able to source materials to start manufacturing.

If you have an interest in how bikes are made, and in particular the weird cult of the two stroke engine, then the Silk story is one that will fascinate you. It is also a typical British tale of the underdog, struggling to succeed against all the odds.

The Silk 700 was one man´s passion, a lifelong dream to re-invent the yowling Scott from his youth. George Silk had restored many 596cc twin cylinder, water cooled Scotts for classic enthusiasts and after a successful performance by a `Silk Special´ at the Barbon Hill Climb in 1970, he started low volume, handbuilt manufacture.

Why Scott ? Well Alfred Angus Scott was a Victorian visionary who designed a sort of prototype Yamaha 350LC back in 1908. With a canted forward 323cc engine, featuring a water cooled upper cylinder block and fuel efficient deflector type pistons, all set in a lightweight cradle frame, the bike dominated road racing so quickly the ACU banned it to give four strokes a chance.

Sadly, the Scott never really developed its full potential, especially after Alf Scott himself went off to make a strange sidecar contraption called a `The Sociable ‘ in the early 1920s. Scott´s finally ceased bike production in the 1950s, when anyone not making dull four stroke singles was on a sticky wicket in the UK market.

The 1970s Silk project was a 653cc updated version of the basic Scott twin cylinder power unit, set in a beautifully crafted steel tubular frame made by Spondon of Derbyshire, who also provided the forks.

George Silk, backed by a Kendal based company called Furmanite, started serious production in 1977, right in the midst of the OPEC oil crises and petrol ration books of the era. It wasn´t a good time to sell a two stroke, especially a handbuilt machine which retailed for £1,984. Sounds peanuts now, but a new 1977 Suzuki GS750 cost £1,285 and was 20mph faster. But George Silk believed his chassis was way superior to the Superbikes of the 70s. Journalists had been harangued for some years regarding the virtues of lightweight two strokes in stiff tubular frames by George, and some went along with the idea.

But the Silk was essentially, an update on a very old engine design, and unlike the Yamaha RD series, or Kawasaki KH triples, the Silk had no race pedigree, and it was marketed as a gentleman´s tourer, which was its great undoing.

In those days, UK bikers aged 25 plus were a bit thin on the ground and young riders hadn’t much hope of raising the £2,000 asking price. However, the Silk 700S was produced at the rate of two machines a week from the Darley Abbey works in Derbyshire in the late 1970s. Customers could choose from five basic paint options; British Racing Green, metallic blue or green, black with gold coachlines or plain red. There was also a special edition in purple and cream, the old Scott colours and co-incidentally, a similar scheme to Silk Cut fag packets. The Silk engine benefited from advances in two stroke technology by Dr Gordon Blair, from Queen´s University Belfast – who were leaders in the field and even had Honda and Suzuki knocking on the lecture theatre doors.

The thermo-syphon cooling system, ( used then by Zundapp in Germany, as well as Silk ) essentially boiled water using engine heat, then fed it back down from the radiator in a rubber tube to the engine cases, where it slowly boiled up again – no water pump was required.

Silk were an engineering company and made the piston port twin cylinder engine in-house at their Derbyshire base. The pressed up, four roller bearing crank had the primary drive taken from the crankshaft centre, to an old Velocette Venom four speed gearbox, which was fitted upside down, so you changed down on the lever to go up the box, like a racebike in fact.

Very odd for most riders. But there was more eccentricity. The engine ran on 50:1 petroil mix, yet had a huge separate three and a quarter pint oil tank reserved for main bearing lubrication, pumped by Silk´s self designed oil pump, which was linked to the throttle. Open the throttle and the oil flowed faster. Seldom was any two-stroke so well lubricated.

Another quirky touch was that the petrol tap was located behind one of the sidepanels, which had to be removed to operate it – not easy switching onto reserve on the M62 then…

The engine´s claimed 48bhp was developed at a mere 6,000rpm, giving the bike touring performance. Peak torque was made at just 3,000rpm, similar to the Suzuki GT750 `Kettle´ of the 70s, and the water jacket gave the unit a strange `woofling´ sort of noise. The twin siamesed exhaust pipes ran into a Spanish made Ossa silencer, which was set so low that spirited cornering could soon ground it – no bad thing on the incredibly skinny ( by modern standards ) tyres fitted.

Wheels were originally 18 inch Borrani alloy rims on early Silks, with six spoke Campagnolo cast items seen on this later 1978 model. The whole bike only weighed 305lbs dry and could hit 115mph, the same as a Z650 Kawasaki which weighed 465lbs.
The Silk 700S pictured here was owned by a Mr. Neil Frost a few years ago, when your roving reporter met him near the Goyt valley in Derbyshire. Neil had bought the Silk because he loved the bold statement that George Silk was making back in the 1970s. He admitted it smoked like a damp bonfire when cold, but once the engine warmed up, it was a surprising economical bike to ride, returning 50-60mpg at a steady 70-ish mile per hour cruise.

Silk buyers could specify their bikes to suit their tastes and Neil´s had the cast wheels, with the larger four gallon fuel tank. It also had the extra Lockheed front disc brake, but all Silks had a rear drum fitted. The final drive chain was invariably enclosed, as were the front forks and Girling shock absorbers. Other high standard spec bits included Lumenition electronic ingnition, a quartz halogen headlight, Renolds chains for primary and final drive, plus tapered roller steering head bearings.

Like Alfred Scott, George Silk was reaching for a higher level of quality. With the Silk 700, George and his partners were striving to pay homage to a great Victorian engineer who had put the two stroke on the motorcycling map. They wanted to create a versatile, economical, lightweight machine for older enthusiasts who placed individuality and durability above all else.

But their machine was too faithful to Scott´s eccentric, purist nature and was already ten years too late for the UK market. The era of cheap petrol and oil had gone forever. Big two strokes were an endangered species as US driven emissions laws began to be adopted in Europe too by the early 1980s.Although Suzuki´s GT750 two stroke outsold the CB750 for a couple of years in Britain in the late 1970s, it was perhaps due more to Barry Sheene´s hero status, rather than the bike´s surprisingly civilised touring performance. Finally, Furmanite ordered Silk 700S production to halt in 1981 when UK bike sales collapsed as the Thatcher recession lowered wages and inflation, via mass unemployment. The silken thread that ran all the way back to Scott´s of Shipley was cut

Source:
https://www.bikemeet.net/forums/topic/silk-700s/&SearchTerms=silk,700s

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