Featherbed frame

1990s replica Norton with replica Featherbed frame

The featherbed frame was a motorcycle frame developed by the British Norton motorcycle company to improve the performance of their racing motorcycles around the twisting and demanding Isle of Man TT course in 1950. It was considered revolutionary at the time,[1] and the best handling frame that a racer could have.[2] Later adopted for Norton production motorcycles, it was also widely used by builders of custom hybrids such as the Triton, becoming legendary and remaining influential to this day.[1]

The Featherbed inspired other frame builders who based their own products on similar principles, including the heavyweight Münch Mammoth and a lightweight version for a 250 cc BSA C15 engine.[3][4]

The Featherbed was replaced by the Norton Isolastic frame in 1967 for the then newly-developed Norton Commando which used a rubber-mounted engine and gearbox,[5] although Norton continued to offer the Mercury with a Featherbed frame until production ceased by 1970. Replicas of the frame continue to be produced by specialist companies.[6][7]

Triton. A Triumph 650 cc pre-unit engine and gearbox in a wideline Norton Featherbed frame

Origins

In 1949 brothers Rex and Cromie McCandless offered Norton a new frame to support their successful 500cc race single. Rex McCandless was a self-taught Belfast motorcycle engineer and raced competitively with his brother on a Triumph Tiger 100. He had made several improvements to the Triumph, notably an innovative new frame with a swinging arm fitted with vertical hydraulic shock absorbers from a Citroen car.[8] BSA bought several of his converted motorcycles but Norton saw the real opportunity and contracted him to work exclusively for them from 1949. The Norton Motorcycle Company were concerned at the reliability of their plunger (or "Garden Gate") frame, as several had broken through the stress of racing. Norton engineer Joe Craig solved the problems by making the frames heavier but handling suffered as a consequence.[8]

Norton commissioned the McCandless brothers to design a complete frame, incorporating a swinging arm. McCandless' finished design was expensive, as it required over forty feet of the best Reynolds steel tubing. It was a welded twin loop with a swinging arm fitted with their own design of shock absorbers, with a heavily braced cross-over headstock. In two months a prototype motorcycle with the new frame was on the test track and it was tested on the Isle of Man in the winter of 1949. It performed well and Norton decided that the Norton works team would have motorcycles with the new frames. The Norton works was not well equipped so the sif-bronze welding was undertaken by the McCandless brothers who produced the eight frames for the racing team by hand.[7]

The patent

Norton applied for a patent for the design on October 13, 1949 and it was granted as reference 664,667 but the completed specification was not published until January 9, 1952. The Featherbed frame was simply constructed.[9]

This invention relates to a new or improved frame for a motorcycle which comprises two substantially parallel rectangular loops each formed from a single length of tubing, and the ends of the tube forming each loop cross and are welded to each other at the top front corner of the loop, the free ends of the tube which extend beyond the crossing point being welded to the side of an inclined head tube adjacent to the top and bottom thereof. The assembled frame is extremely strong for its weight and designed to provide the maximum resistance to any stresses applied to the frame by road shocks or by the driving torque of the power unit.

The Featherbed name

Harold Daniell was a successful Isle of Man TT racer with three victories and several placings in the Tourist Trophy races and the Manx Grand Prix.[10] After testing the new Norton frame in 1950 he declared that it was like "riding on a featherbed" compared with riding the "garden gate[11]" — and it has been called the featherbed frame ever since.[12]

The term feather bed was used in the 1933 to 1938 Brough Superior catalogs in their press section. As printed in the 1933 Brough Superior catalog:

The "Brough Superior" Rear Spring Frame, to quote "Castor" of "Motor Cycling," renders "pitching or wobble non-existent, impossible. A feather bed could scarcely be safer" -- and this in relating his experience on a Special "Brough Superior" S.S. 100, on which he did 106 m.p.h. in second gear on the road ![13]

Racing success

Further testing took place at Montlhery race track with four motorcycles running flat-out for two days. The new frame stood up well to tests and saw its UK launch at Blandford Camp in Dorset in April 1950. Geoff Duke had won the Senior Clubmans TT and the Senior Manx Grand Prix in 1949 on the earlier type Nortons, so was a clear choice for Norton to really put the new Featherbed-framed race bikes to the test. Duke won the race on the new design and several racing successes followed with Norton winning first three places in the 1950 Senior and Junior TT's.[8] Duke set a new lap record of 93.33 mph and also broke the overall race record, finishing in two hours, 51 minutes and 45 seconds. He then went on to finish second in the Junior TT. (Harold Daniell's Norton was third.) When it came to the bends on the twisting Island course the new frame gave the Nortons a distinct advantage.[7]

Featherbed frames were also successful modified for use in off road racing or motorcycle scrambling.[14]

Featherbed variants

Manx racer in Reynolds 531

Weight and strength were key factors in the design of the featherbed frame for the Norton racing team's Manx. 16- Gauge Reynolds 531, a high-tensile manganese-molybdenum steel alloy, was used as it allowed the frame tubes to be made thinner for the same strength, as well as making for a more responsive frame. All the joints were Sifbronze welded,[15][16] – a relatively low-temperature flame-braze – except for the sub frame which was initially bolted-on but welded in later versions.[17]

Norton International

In 1953 the Norton International was relaunched with a new version of the Featherbed frame made from grade A mild steel.[18]

Single and Twin cylinders in Featherbeds

Having earlier installed the Dominator twin-cylinder engine of 500 cc and 600 cc, in 1959 Norton put the old single cylinder Model 50 (350 cc) and the ES2 (500 cc) into the Featherbed frame to rationalise production. Using grade A mild steel, the size of this engine determined the space between the top and bottom rails of the full duplex cradle. In 1960 the top rails were installed at the rear of the tank.[19] Riders complained that these wideline Featherbed frames were uncomfortably wide at 11.5 inches (29 cm) but it was not until 1960 that the top runs of the frame were narrowed towards the front of the seat, with corresponding overall styling changes including tank and seat to create the slimline frame.

The slimline was used until the last of the vertical twin cylinder models in the late 1960s, the Norton Mercury, a limited-production run of single carburettor 650 cc machines based on the Dominator, the Norton Commando with its new frame design and angled-forward engine having been launched at the Earls Court show in 1967.[20]

References

  1. ↑ 1.0 1.1 Motorcycle handling and chassis design: the art and science by Tony Foale. 2006
  2. ↑ The Café Racer Phenomenon by A Walker. 2009
  3. ↑ Motor Cycle, 3 February 1966, pp.142-143 On the Four Winds by 'Nitor'. Accessed and added 2014-09-28
  4. ↑ Motor Cycle, 24 November 1963, pp.696-699 All the rage by John Ebrell. " ...Ilford's CeeR-Speedshop. For £29 they'll supply the C15 rider with a featherbed-type duplex frame". Accessed and added 2014-09-28
  5. ↑ Norton By Mick Woollett. 2004.
  6. ↑ Andover Norton Frames and Auxiliaries made to factory drawings Retrieved 2014-09-28
  7. ↑ 7.0 7.1 7.2 Myatt, Steven. "Featherbed frame". Retrieved 2009-01-03.
  8. ↑ 8.0 8.1 8.2 d'Orleans:, Paul. "Rex McCandless and the Featherbed Frame". Retrieved 2009-01-03.
  9. ↑ "Patent Specification". Retrieved 2009-01-09.
  10. ↑ IOMTT.com Harold Daniell results database (retrieved 5 November 2006)
  11. ↑ Garden gate is a reference to the plunger frame Nortons of this era
  12. ↑ "Harold Daniell". Retrieved 2009-01-03.
  13. ↑ "Brough Superior". Retrieved 2010-04-27.
  14. ↑ Off-Road Giants!: Heroes of 1960s Motorcycle Sport by Andy Westlake
  15. ↑ SIF Bronze – Suffolk Iron Works, Graces Industrial Guide. Retrieved 2013-08-24
  16. ↑ Commercial Motor Archive – Sifbronze Works. Retrieved 2013-08-24
  17. ↑ Currie, Bob (1993). Classic British Motorcycles. Chancellor Press. ISBN 1-85152-250-6.
  18. ↑ "Norton International History". Retrieved 2008-12-24.
  19. ↑ "The Origin of the Famous Norton Featherbed Frame". Retrieved 2009-01-03.
  20. ↑ Real Classic Norton Mercury Retrieved 2014-09-28

External links