Together at Last
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Together at Last Rebuilding motorcycles is more fashionable today than ever before. But when it comes to fulfilling a 40-year-old dream, enthusiastic tinkering is no substitute for methodical planning and execution. Given enough money, you can build any motorcycle. When it comes to replicas of famous racing machines or reborn “old flames”- there is no shortage of brand or model specialists. But if it’s something that has never been done before, experience says it will take time, patience, negotiation and hard work as well as money. This project , a motorcycle with a Norton Commando engine and Rob North frame is typical. The builder lives in Liechtenstein and prefers to remain anonymous. His resumé is typical of many biker/ mechanics; boundless enthusiasm and adventurous experiences with his first lightweights, then technical problems with the first heavy machines, followed by extensive training as a vehicle technician, designer and, finally, engineer. Starting a family, his professional life, other hobbies initially put motorcycling on hold. But memories of brisk English twins kept coming back. A bevel drive Ducati would also have been possible, but the great fascination had always been Formula 750 and long-distance racing machines from the early 1970s. As a technician, he had closely followed the efforts of a number of european suspension specialists. In particular, the performance of the English frame builder Rob North, whose frame helped the Triumph and BSA triples to an unexpected winning streak from Daytona to Le Mans in 1971. Replicas of the triples are relatively easy to find, but it had to be something very special. The goal was a street legal motorcycle with a Norton twin engine and the Rob North frame. Robin "Rob" North had trained as a turner and welder when he, passengered by his wife, competed in sidecar racing from 1958 onwards, with Triumph twins in the Norton featherbed frame. These were always problematic, with twisting and cracking around the steering head. In the course of the 1960s, North developed a whole series of complete frames for racing teams and speedway motorcycles. Based on his experience with tube fracture, he always preferred Accles & Pollock's T45 (carbon-manganese steel) instead of the usual Reynolds 531 (steel, manganese, molybdenum). The frame construction that Rob North finally realized for his friend Percy Tait featured two continuous tubes, connected to the steering head, but not crossing like the Norton featherbed, and distinctly angled downwards, directly leading to the swinging arm pivot. The triumph tester and racer wanted to start in 1969 with a 750cc twin cylinder test engine. At the end of the season, he brought a triple to Rob North's workshop. The tube routing was retained, but widened further to accommodate the wider engine including carburetor and a central oil tank. Triumph chief designer Doug Hele proposed welded box sections for the engine and swinging arm mounts. Following the prototype, in November 1969 the Triumph racing department placed an order for eight frames, which were to be ready to race by the start of the season in March 1970 in Daytona, Florida. Frame loops and swingarms were crafted from 11/4” tube with a wall thickness of 1.4 millimeters, the rear frame from 7/8” material with wall thickness of 1.6mm. North brazed the hand-bent tubes. Each frame took 30 hours to complete. A number of small workshops around Coventry provided fabricated sheet steel triple trees, aluminum tanks and numerous small parts. Additional frames were required for the 1971 season, initially four, finally six. North now set the steering head 50 millimeters lower and at an angle of 28 instead of 30 degrees. The engine was moved forward 11/2” and raised by the same amount, the upper frame tubes placed even closer above it. Wider triple trees allowed the use of a double disc braked front wheel. Triumph is said to have withheld Rob North’s fees, so in 1973 he tried his luck in California The Triumph and BSA racing program was considerably curtailed in 1972. However, North had already begun his own initiatives in the USA and so Rob North moved to Southern California in early 1973, where he is still involved in frame construction and motorcycle repairs. According to his own records, he completed a total of 91 frames over the years, starting with the Daytona BMW 1973/74 and the Honda CB 750 and later superbikes. English specialists did much more business with the Rob North frame than did its actual creator. There is talk of a good 500 pieces since the seventies for racing machines- which could transfer directly from the current racing scene to the classic scene- and enthusiast machines. After the closure of the Racing department and the demise of successor NVT, the London engineering firm Miles Engineering approached Rob North for an official agreement to build additional frames. From 1974 Mick Pearce was entrusted with this task. When Les and Denise Whiston launched Trident MCS in Dudley, West Midlands 30 years later to continue Miles's program, Mick Pearce intended to introduce new people to the Rob North frames and then retire. But as it turned out, he stayed. And that was exactly the stumbling block for the Rob North Commando project, because Mick Pearce flatly refused to manufacture a frame for the use of a motor other than the "Triple". However, our builder had already accumulated Norton components, including original Rob North yokes, Lockheed brake parts from the seventies and a matching Ceriani fork. Finding a genuine frame had long since proven to be a hopeless task, alternative Rob North copies were considered too risky, so he kept at Trident MCS with patience and persistence. In the meantime, he had CAD designs for engine and transmission mounting plates, shock absorbers and sprocket carriers for the rear wheel. This clean work combined with the firm assurance that frames, swingarms and tanks would be ordered without any modification, since changes for the Norton project would then have to be made independently, Mick Pearce was finally able to change his mind. As usual with Norton, the motor and gearbox were held in the frame by common mounting plates. Instead of the triplex primary chain, a belt drive was used. The isolastic mountings were dispensed with, only a damping rubber was retained for the cylinder head steady. The rigid mounting required the crankshaft to be balanced accordingly. The correct positioning, with respect to center of gravityand clearance of the carburetor and oil tank, was the result of lengthy considerations and measurements. The various phases of the trial assembly required further changes to the petrol and oil tank, footrest hangers and exhaust system. A heavily modified Norton Commando Mk III cush drive were used. The centre stand, toothed belt cover, chain guard and seat had to be made. The front hub came from a Triumph Trident, the 18-inch rims from Borrani, the fender from Ducati, the brackets for the Lucas headlamp from Tommaselli, the clip-on handlebars from Magura and the Conti-like exhaust system NOS Campbell. It goes without saying that the motor is no normal Norton twin. The crankcases and the RH4 cylinder head (32 mm inlet ports) are Commando 850. However, since he happened to have a crankshaft, steel connecting rods and the high dome pistons from the short-stroke motor, that is what it was to be. Norton did not manufacture the 750 short stroke. Tried and tested tuning methods delivered 74 to 76 HP The short-stroke Norton motor of 1973, was intended as a new sporting variant of the 750, described in the brochures but never delivered. The components already in stock later disappeared in all directions. Since then, hardly anyone has been able to do anything with them. For the last remaining purpose, sidecar Moto Cross, the short-stroke mill was not very suitable due to its narrow power band. Instead of the standard 850 Commando iron barrel, a five kilograms lighter aluminum cylinder (with liners) from Norton tuner Steve Maney is fitted. With the 77-millimeter original pistons and the stroke shortened from 89 to 80.4 millimeters, displacement is 748 ccm and compression ratio of 10.5: 1. The valve train came from Jim Schmidt from California, who has already supplied the parts for numerous current racing Nortons. Tappets made of steel instead of cast iron, sliding in bronze guide blocks instead of directly in the block, improved pushrods and the matching camshaft seemed a good idea. Brass exhaust nuts replaced steel. Valves, porting and combustion chamber remained unchanged; 32-millimeter Keihin carburetors replaced the Amal Concentric on specially designed adapters with rubber sleeves. Their choke operation required a sophisticated construction under the deep tank. A lot of brainpower also went into the crankcase breathing via the timing case and the safe and vibration-damped oil tank mounting. The Lucas alternator was reused with a new holder for the stator, a digital ignition system Sachse ZDG3 with three selectable adjustment curves was preferred over products from England, New Zealand or Australia. Belt drive and multi-plate dry clutch were supplied by Bob Newby from England. The Norton Commando four-speed transmission was overhauled and installed without modifications. A really good swing on the Iong Kickstarter - Triumph Trident T 160 - relatively high up on the otherwise very compact motorcycle sets off a rough, aggressive tone from the two "silencers". The very sporty custom seating position works for the builder. With a dry weight of only 162 kg (certified by the TÜV; for comparison: factory triumph 172 kg, factory Norton 159 kg, Commando Production Racer 175 kg, Commando Roadster 181 kg), “sufficient” engine power of "around 70" HP, playfully easy handling and triple disc brakes - the dream has apparently become reality.