Silk Sabre Smooth as
The superb 1977 Silk 700S Mk2 Sabre featured in this article is owned Andy Roxburgh. It is a low mileage (only 10,798 miles on the clock) original condition machine that looks almost factory fresh, finished in a striking red set off by the gold coloured Campagnolo cast wheels and the polished chrome work. Andy currently uses it for rallies and runs, it was recently seen on the Vintage Car Club of NZ National Rally at Dunedin. Once it is over 40yrs old (when NZ registration costs fall dramatically) Andy intends to use it a lot more as it is a very practical and reliable machine. The story of Silk motorcycles and how this unusual machine arrived in New Zealand from the UK is quite intriguing. Bob Cleare, of Auckland, was impressed by the press reports about the Silk and wanted to buy a new Silk 700S Mk2 Sabre. Bob contacted George Silk in 1980 but found out that they were no longer being produced.
However, George suggested buying a low mileage second-hand machine and having it overhauled by Silks. George knew of two suitable machines that were for sale and Bob bought one of them, a 1977 Silk Mk2 Sabre. The red Silk 700S Mk2 Sabre was imported to New Zealand in 1981 with only 2,000 miles on the clock. It went through three further owners before Andy acquired the machine in 2007. George Silk and Maurice Patey started Silk Engineering at Darley Abbey, Derbyshire UK in the late 1960s. The company was set up to provide spares, repairs and restoration services for Scott motorcycles, they also offered a range of modifications to improve the reliability and performance of Scotts. Whilst previously working for Scott specialist Tom Ward, George Silk fitted a Scott engine into a Spondon racing frame, which he continued to race and develop after starting Silk Engineering. After some success with his Silk Special, he began building a road-going prototype. Silk Engineering exhibited the prototype at the 1971 Racing and Sporting Motorcycle Show in London. Orders far exceeded their capability to produce them but 21 Silk-Scott Specials were handbuilt between 1971 and 1975. As the supply of Scott engines dried up customers were asked to find their own. The situation became even more difficult when Matt Holder, who owned all the manufacturing rights to the Scott motorcycle, disputed the use of the Scott trademark. Holder also refused Silk’s request to make Scott engines under licence, forcing them to develop their own engine. The new two-stroke engine was designed and developed by George Silk and David Midgelow (moonlighting from Rolls Royce). Firmly based on the original Scott engine it incorporated a number of improvements. They were also assisted by two-stroke expert Gordon Blair of Queen’s University, Belfast, who optimised the porting with the aid of specialist computer programmes. A precision engineering company, Silk was able to make the piston port twin cylinder engine at it’s Derbyshire workshops. The new engine retained deflector pistons (which gives good mid-range torque and fuel economy) but with porting improvements and a capacity of 653cc,
it produced significantly more power than its Scott ancestors. The pressed up, four roller bearing crank was a great improvement over the fragile overhung crank of the Scott. The engine ran on a 50:1 petroil mix, with a separate oil tank reserved for main bearing lubrication fed by Silk’s own design of oil pump. Silk’s variable delivery pump was a great improvement over the Scott’s fixed delivery Pilgrim pump, ensuring correct oil delivery without too much smoke. A thermo-syphon water cooling system was retained but a new radiator and separate header tank much improved what was always a marginal system on a Scott. State of the art electronic ignition replaced the Scott’s magneto and twin siamesed exhaust pipes fed an Ossa silencer. The 653cc engine’s claimed 48bhp was developed at 6,000rpm, giving good touring performance, and peak torque was at 3,000rpm, comparable to the Suzuki GT750. The transmission was also upgraded but like the Scott the primary drive was taken from the centre of the crankshaft. The new transmission followed Scott’s tradition of using a Velocette gearbox and clutch by using an inverted Velocette Venom fourspeed gearbox and clutch. The final drive chain was fully enclosed for longer life, with the upper and lower runs being encased in “telescopic” rubber gaiters. The Silk 700S was launched in 1975 with the new engine in a specially designed steel tubular frame made by Spondon of Derbyshire, who also made the forks, yokes, disc/drum brakes and rotors. Priced at £1,355 it was the most expensive production motorcycle of the time. From the outset the Silk 700S had an excellent power-to-weight ratio, which combined with superb handling, enabled it to compete with some of the best road bikes of the time. The claimed top speed was an impressive 110 mph. However with no electric start, and the kick-starting technique taking some practice to perfect, it was always going to be an enthusiast’s machine.
The 700S continued to be developed along with the SPR Production Racing version. Deliveries were slow with just two motorcycles a week coming off the production line. Customers could select a range of options and choose from five basic colour schemes – British Racing Green, metallic blue or green, black with gold coach-lines or plain red. There was also a “Silk Scott special edition” in purple and cream, a very distinctive colour scheme previously used on Scotts.
The other striking feature was how relatively small and light the Silk was, with a 54inch (1370mm) wheelbase, 18inch wheels and weighing only 310lbs (141kg), it was more like a 350. It was even more noticeable when alongside some of its bloated 1970s contemporaries. Early Silks had spoked 18inch Borrani alloy rim wheels, these were later superseded by six spoke Campagnolo cast wheels. Silk Engineering was taken over by the Kendalbased Furmanite International Group in 1976 who continued production of the Silk 700S. In 1977 it was upgraded to the 700S Mk2 and called the Sabre. Improvements from the Mk 1 included finned cylinder barrels, a redesigned seat, instruments and rear light nacelle and Lockheed brake calipers. The last batch of machines had some further porting and timing improvements, which with increased compression raised power to a claimed 54bhp. In 1978 the 100th Silk motorcycle was produced, production continued until December 1979 when the company realised they were losing £200 on each machine that they were selling for £2482!
The last Silk motorcycle ever built was Clive Worrall’s 500 cc model, based on a prototype that was never put into production. It was used as a competition prize for Classic Bike magazine. A twostroke Trials prototype, the Silk 350, was also developed but also never went into production.
The Silk is much easier to live with than its, at times, fickle predecessor the Scott. Once the kick starting technique is mastered, starting with the electronic ignition is easy. Bursting into life with the very familiar, Scott like, burbling exhaust note, it idles nicely. Pulling away, the clutch is slipped until it is doing 10mph due to the rather tall first gear. The broad spread of torque makes for brisk acceleration and is well matched to the 4 speed gearbox. Accelerating through the gears produces a distinctive, Scott like, “yowling” exhaust note. As you would expect from a racederived frame it handles superbly ridden solo. The excellent brakes, twin discs up front, are bordering on being too powerful for such a light machine. The factory (and some road tests) claimed it would do 110mph but Andy has not exceeded 80mph and feels the top speed is probably more like 100mph. The inherent smoothness of a 2 stroke twin and broad torque makes for stress-free riding. Ridden sensibly it returns about 55mpg thanks to the deflector pistons and 200 miles can usually be achieved on the contents of the 4 gallon tank. However like most 2 strokes petrol consumption increases significantly when really winding it on. It uses about a pint of GP50 oil every 300miles. The only real problem Andy has had in the last 9 years is with the 12v Lucas electrics but a new regulator box solved the issue. The only other issue is the small dual seat which is set a fair way back (a hangover from the frame’s racing heritage), it is not best suited to riding with a passenger.
Andy’s Silk 700S Sabre is an unusual, distinctive, but very practical machine that any discerning collector would like to own. The Silk offers one man’s vision of what Scott’s should have developed into if the company had stayed true to its principles of performance, light weight and good handling (rather than the ponderous, overweight, underpowered machines produced by Matt Holder in the late 1950s).