Norton Commando 1968-1977
From 1968 until the demise of the company in 1977, the Commando was the main bike in Norton's lineup. Powered with first a 750cc engine later enlarged to 828cc, the Commando was offered in several models to fit the styles of different riders and riding styles. Performance, mechanical simplicity, and a unique engine mounting system are all hallmarks of this classic British machine.
British Parallel Twin
The British twin-cylinder motorcycle engine dates back to 1938, with the 500cc Triumph Speed Twin designed by Edward Turner. In 1950, engine displacement was increased to 650cc.
Bert Hopwood engineered the first Norton twin in 1949, the 497cc Model 7, which grew into the 650cc Dominator, and then the 750cc Atlas, lastly being launched in 1967 as the 750cc Commando. It was the last of the Norton parallel-twin machines.
Throughout the Forties and Fifties, British bikes dominated motorcycle performance and racing venues. However, by the late Sixties, Japanese manufacturers started producing faster, cheaper, and more reliable motorcycles, severely cutting into the sales of both British and American-made bikes. The Norton Motorcycle Company had neither the time nor money to develop a new engine. Their parallel-twin engine was powerful enough, but suffered from terrible vibration. Previous attempts at rubber-mounting the engine helped marginally.
Norton's Chief Engineer Bernard Hooper, Dr. Stefan Bauer, and assistant Bob Trigg, devised a system where the engine, gearbox and swing-arm assembly were bolted together and isolated from the frame by special rubber mountings. The suspension system kept the swingarm true in relation to the engine position, while isolating the rest of the chassis from the vibrations of the engine. Instead of the engine being rigidly bolted to the frame, it is hung off the main frame, via two cross-frame tubes, one at the front of the engine and one at the rear of the subframe.
Bolts holding the powertrain assembly to the main frame pass through rubber buffers in the tubes, isolating the engine from the frame. This allows the engine to "float" on the vertical plane, with lateral movement controlled by shims in the mounts. This eliminated the extreme vibration problems that were apparent in other models in the range, as it effectively separated the driver from the engine.
Norton took their 750cc Atlas engine (actually 745cc) and developed a new frame, tipping the engine slightly forward The Isolastics anti-vibration system did reduce vibration, as long as the required free play in the engine mountings was at the correct level. Too little play brought the vibration back and could crack the frame, and too much play brought handling issues,particularly fishtailing in high-speed turns.
750 Norton Commando
The 750cc Commando Mark 1 Fastback was introduced in 1968. It was soon joined by the 750-S model. which had high-mounted left-side exhaust and a smaller 2.5 gallon gas tank. In 1970 the updated S model, called the Roadster, had conventional low exhaust pipes, featuring upward-angled silencers with reverse cones.
September of 1970 saw the introduction of the Fastback Mark 2, with a modified stand, chain guard and alloy hand levers. The Street Scrambler and the Hi Rider appeared in 1971, along with the Fastback Long Range, which featured a larger gas tank. Front disc brakes appeared late in 1971.
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In 1972, the Combat engine was introduced with the appearance of the Mark 4 Fastback, along with an updated Roadster and the 750 Interstate. The Combat delivered 65-horsepower at 6500 rpm with a 10:1 compression ratio, but main bearing failures and broken pistons were common.
750 Commando Mark V
The last of the 750 series, the Mark V was produced from November 1972 to mid-1973 as a 1973 model. Engine bearings were improved and compression was reduced to 9.4:1, both helping engine reliability. 1973 also saw the Long Range model discontinued.
850 Commando Mark 11
Starting in April 1973, Commando engines used a bore and stroke of 77mm x 89mm. Displacement was 828cc and advertised as 850cc. The cylinder head of the earlier 750cc engine, well designed and factory-ported, was retained. Compression was further reduced to 8.5:1 with the engine now producing 60-horsepower at 5,900 rpm. Increased torque from the longer stroke seemed to make up for the reduced horsepower. In 1974, the Commando lineup included the Roadster, Mark 2 Hi Rider, and Mark 2a Interstate.
John Player Norton Commando
A fourth Commando model was also offered in 1974. Marketed to comply for U.S. racing rules, the John Player Norton (JPN) model was introduced in late 1973 and reached the public in 1974. It was available with either the 750cc short-stroke engine, or the Mark 2A 828cc engine. Approximately 200 John Player Norton replicas were produced and all had right-side shifters.
850 Commando Mark 111
Due to popular request, electric start was introduced on the 850 Mark 111 Commando. Fortunately the kick start was retained, as the electric starter was not completely reliable. A front disc brake also appeared about this time.
For the Mark III, the Isolastics system was upgraded. A paired spring rated to carry the weight of the engine and transmission assembly was designed, taking the load off the Isolastics mounts.
1975 models, now weighing 460 pounds, were reduced to just two machines, the Mark 111 Interstate and the Roadster. Both machines had a left side gear shift and right foot brake to comply with United States vehicle regulations. These models remained unchanged until October 1977 when the last machines were made.
Norton Commando Performance
In the March 1970 issue of Cycle magazine, tests were made on all then-current superbikes. Of the seven bikes tested, a Norton Commando SS ran the quarter-mile fastest, at 12.69 seconds. The Honda CB750 stopped more quickly, but the Norton was still faster.
The Norton Commando is one of the most prized bikes in today's classic scene, giving excellent performance and very good parts availability. Over the years it has remained one of the most desirable classic British bikes, and many say it was the best.
The Isolastics anti-vibration system, while reducing vibration, needs regular maintenance. On the last Mark 111 Commandos adjustment was easier, and a conversion to the later Isolastics is available for earlier models.
Although the Norton parallel-twin engine was reliable and well-engineered, the bike's electrics were suspect and accounted for much of breakdowns. However, over the last several decades, many component updates and improvements have been offered.