Classic Metal Silk 700s
This clever stroker deserved a better fate
Story: Ian Falloon
The British are renowned for eccentricity, and many of the most eccentric seem to emanate from the north of England. Some of the more unusual British motorcycles also originated in the damp north. Panther came from Cleckheaton, Dot from Manchester, and the two-stroke Scott smoked out of Shipley.
The Scott motorcycle was unique and ground-breaking. Alfred Angus Scott designed the liquid-cooled two-stroke twin back in 1908. The Scott was so advanced it immediately dominated road racing and was banned to give four-strokes a chance. Unfortunately by the 1920s Alf Scott lost interest in developing his twin, but he left a legacy that was continued 60 years later by George Silk.
Silk was passionate about the Scott, and his lifelong dream was to re-invent the yowling Scott from his youth. The Silk 700 became one man’s lifelong ambition.
The extraordinary thing about the Silk was that while Norton and Triumph were sliding into bankruptcy, Silk and his small band of craftsmen were able to initiate motorcycle manufacture. But the odds were well and truly against him. The oil crisis of 1974 ensured the era of cheap petrol and oil had gone forever and big two-strokes were an endangered species as US-driven emissions laws were adopted in Europe.
Just as Suzuki and Kawasaki were discontinuing their larger two-strokes Silk was establishing his. And the Silk was unlike any other two-stroke of the 1970s. The 653cc twin-cylinder engine kept Scott’s original deflector pistons. These dramatically reduced the amount of unburnt fuel escaping through the exhaust ports, resulting in improved torque and economy at the expense of outright power.
Another unusual feature was the cooling system. No water pump was required as the thermo-syphon cooling system circulated water using engine heat. The heated water rose from the engine into the radiator then flowed down through the radiator as it cooled and returned via a hose to the engine cases, completing the circulation loop.
A single 32mm Amal carb and two-into-one expansion chamber from Ossa in Spain also boosted bottom-end drive. With 35.3kW (48hp) produced at 6000rpm and maximum torque at a lowly 3000rpm, Silk reasoned there was no need for more than four gears. So rather unusually he hooked the pressed up, four-roller-bearing crank with central-chain primary drive to an old Velocette Venom four-speed gearbox. This was fitted upside down, so the gearshift pattern was reversed. It was disconcerting for most riders.
The Silk bristled with eccentricity and the engine was exceptionally well lubricated. It ran on 50:1 petroil mix, yet had a huge separate oil tank for main-bearing lubrication, linked to the throttle. Open the throttle and the oil flowed faster. Another quirky touch was the petrol tap located behind one of the side panels, which had to be removed to switch onto reserve.
One of the most outstanding features was the beautifully crafted tubular-steel Spondon frame. Silk buyers could specify their bikes to suit their tastes – some had traditional wire wheels, others cast alloy. All Silks had a rear drum brake and the final-drive chain was invariably enclosed.
The Silk may have had vintage origins but on the road it set the standard for handling in the late 1970s. Capable of nearly 180km/h and with a wet weight of only 140kg, it was a formidable back road machine.
But its timing was wrong and the Silk was never destined to survive. There was no market for expensive, environmentally-unfriendly, hand-built, high-quality motorcycles in Thatcher’s Britain of the 1980s.
Many thanks to Allen and Lorraine Smith of the Australian Motorcycle Museum at Haigslea, Queensland, for the use of the Silk 700S (built December 1975)
Story: Ian Falloon
The British are renowned for eccentricity, and many of the most eccentric seem to emanate from the north of England. Some of the more unusual British motorcycles also originated in the damp north. Panther came from Cleckheaton, Dot from Manchester, and the two-stroke Scott smoked out of Shipley.
The Scott motorcycle was unique and ground-breaking. Alfred Angus Scott designed the liquid-cooled two-stroke twin back in 1908. The Scott was so advanced it immediately dominated road racing and was banned to give four-strokes a chance. Unfortunately by the 1920s Alf Scott lost interest in developing his twin, but he left a legacy that was continued 60 years later by George Silk.
Silk was passionate about the Scott, and his lifelong dream was to re-invent the yowling Scott from his youth. The Silk 700 became one man’s lifelong ambition.
The extraordinary thing about the Silk was that while Norton and Triumph were sliding into bankruptcy, Silk and his small band of craftsmen were able to initiate motorcycle manufacture. But the odds were well and truly against him. The oil crisis of 1974 ensured the era of cheap petrol and oil had gone forever and big two-strokes were an endangered species as US-driven emissions laws were adopted in Europe.
Just as Suzuki and Kawasaki were discontinuing their larger two-strokes Silk was establishing his. And the Silk was unlike any other two-stroke of the 1970s. The 653cc twin-cylinder engine kept Scott’s original deflector pistons. These dramatically reduced the amount of unburnt fuel escaping through the exhaust ports, resulting in improved torque and economy at the expense of outright power.
Another unusual feature was the cooling system. No water pump was required as the thermo-syphon cooling system circulated water using engine heat. The heated water rose from the engine into the radiator then flowed down through the radiator as it cooled and returned via a hose to the engine cases, completing the circulation loop.
A single 32mm Amal carb and two-into-one expansion chamber from Ossa in Spain also boosted bottom-end drive. With 35.3kW (48hp) produced at 6000rpm and maximum torque at a lowly 3000rpm, Silk reasoned there was no need for more than four gears. So rather unusually he hooked the pressed up, four-roller-bearing crank with central-chain primary drive to an old Velocette Venom four-speed gearbox. This was fitted upside down, so the gearshift pattern was reversed. It was disconcerting for most riders.
The Silk bristled with eccentricity and the engine was exceptionally well lubricated. It ran on 50:1 petroil mix, yet had a huge separate oil tank for main-bearing lubrication, linked to the throttle. Open the throttle and the oil flowed faster. Another quirky touch was the petrol tap located behind one of the side panels, which had to be removed to switch onto reserve.
One of the most outstanding features was the beautifully crafted tubular-steel Spondon frame. Silk buyers could specify their bikes to suit their tastes – some had traditional wire wheels, others cast alloy. All Silks had a rear drum brake and the final-drive chain was invariably enclosed.
The Silk may have had vintage origins but on the road it set the standard for handling in the late 1970s. Capable of nearly 180km/h and with a wet weight of only 140kg, it was a formidable back road machine.
But its timing was wrong and the Silk was never destined to survive. There was no market for expensive, environmentally-unfriendly, hand-built, high-quality motorcycles in Thatcher’s Britain of the 1980s.
Many thanks to Allen and Lorraine Smith of the Australian Motorcycle Museum at Haigslea, Queensland, for the use of the Silk 700S (built December 1975)