Retrospective: Norton 850 Commando Mark III: 1975 – 1977

This Mark III was the last of the genuine Nortons. In October of 1977 the final Norton rolled off the line, with the side
panels reading “850 Commando Electric Start.”

The engine was an air-cooled parallel twin, inclined forward a few degrees, with two overhead valves per cylinder. A pair of Amal Concentric carbs fed fuel into the cylinders, with coils and points sparking the plugs. The whole engine/transmission/swingarm used an Isolastic Anti-Vibration System, with rubber mounting components serving to keep the vibes away. And, of course, an electric leg.

Slip back to November of 1948, almost 30 years before. At the Earls Court show, the annual offering of new models at this London exhibition hall, Norton rolled out the Model 7, a 500cc vertical twin. The engine design was certainly not an original idea, as Edward Turner had done this for Triumph in 1937, but one of his assistants, Bert Hopwood, had moved to Norton in 1947 as Chief Designer.

The vertical twin was in the late 1940s what the UJM design (the Universal Japanese Motorcycle, an air-cooled in-line four that was initiated by Honda’s CB750 in 1969) was in the 1970s. Many of the British motorcycle manufacturers—AJS, Ariel, BSA, Matchless, Royal Enfield—went to the vertical-twin design because it worked, and people wanted it. Coincidentally, Hopwood worked at many of these factories over his 40-year career.

The Model 7’s frame was a full cradle with plunger rear suspension, used by Norton’s ES2 500cc single; the chassis plays a major role in this story. The follow-up model was the 1952 Dominator 88, using more or less the same engine, but this one was housed in a Featherbed frame with a swingarm rear suspension having twin shock absorbers. In ’56, the engine was bored and stroked to make it the 600cc Dominator 99. The magneto went away in ’58, and coil ignition came in. In ’61, the engine was stroked to produce a nominal 650cc. In 1962, Hopwood’s essential engine was bored out yet again to come up with the 750cc Atlas—it had a bore of 73mm and stroke of 89mm, equaling 745cc. This was well beyond Turner’s dictates that the best parallel-twin engine would be no more than 650cc running at a maximum of 6,500 rpm. Run an Atlas up to that rpm and the fillings would fall out of your teeth.

The British motorcycle industry was falling apart, much of it due to the vibration on the vertical twins. So Norton hooked its chief engineer, Bernard Hooper, up with a new hire, Stefan Bauer, who had been working with Rolls-Royce. Knowing that if they could isolate the engine from the rider, sales would improve, so they came up with the Isolastic system—Hooper holds the patent. At the front of the engine a spindle ran through two holes, with a rubber doughnut on each end. The same setup was on the back where the swingarm came through. The pistons and crankshaft whirr round and round, vibration builds and is dissipated through the rubber. Knowing that nothing stays quite the same with all that vibration, Hooper and Bauer arranged the Isolastics so that they could be loosened or tightened, using shims.

Introduced as a 750 in 1968, the riding public loved the Commando. Racers tightened things up for a better feel to the handling, putting up with increased vibes, while the lazy day-rider just let things go—ending up with a rather rubbery handling situation. Most people who have ridden aged Commandos have commented on the wobbly feeling—due only to lack of maintenance.

A second problem was power. The 750 was rated at 51 horsepower at 6,250 rpm, but after the introduction of the Honda CB750 the Norton marketing types felt more power was needed. In January of 1972 Norton offered the Commando with the high-compression (10:1!) Combat engine, claiming 65 horsepower at 6,500 rpm. Which it might well have put out—until it exploded.

Well, heck, if that won’t work, let’s just make a bigger engine. So in 1973 that old Hopwood device was bored out yet again, this time to 77mm, giving a total of 828cc—call it an 850. With a modest 8.5:1 compression ratio, the factory claimed 60 horses at 6,200 rpm. About the only internal modification was a slightly lighter flywheel to compensate for the heavier pistons. With a small fairing and a change in the gearbox sprocket, a very carefully fettled 850 was timed at 142.75 mph; this feat got headlines. For ’74, the Mark II models were on the market with minor styling changes.

Early in ’75 the Mark III entered showrooms with two models, the sporty Roadster and the touring Interstate. By then U.S. law had standardized shift patterns and Norton had to swap the brake pedal with the gear shift. Not a problem, though now the gearbox was fixed, and the primary chain had an automatic hydraulic tensioning device. The Commando had been given a front disc brake in 1972, and with this conversion got a rear disc as well.

To simplify maintenance, the Mark III models had easily adjustable front and rear Isolastic units, requiring no special tools. A sloppy suspension was the rider’s fault, not the manufacturer’s.

Of great interest was the electric starter. This was a Prestolite device which was fitted right behind the left cylinder, roughly where the magneto had been until 1958, and a series of gears went down to a sprag one-way clutch that was fitted to the crankshaft. Pull in the clutch lever (normal clutch, not sprag), kick through, free the plates, open the petcocks, tickle the carbs, turn the ignition on, and push the button. The company recommended “starting in neutral with the clutch disengaged.” If the engine was warm and the battery fully charged, it might start. But the 12-volt battery was just not strong enough to give the engine any real spin. If it did not start right away, the human leg would have to do the work; Norton had the good sense to leave the kickstarter in place. Anybody riding a Mark III today has probably installed a stronger Nippondenso starter…the marvels of progress.

However, by 1976 Norton’s finances were, in a word, disastrous, and banks were calling in their loans. Production of the Hopwood-engined motorcycles ceased in the fall of 1977.

PS: But is Norton back in the game? In 2010 the new Norton Motorcycles brought a stock Norton 961SE out to the Bonneville Salt Flats where it ran a record-breaking 129.38 mph. This bike runs an air-cooled, 961cc parallel twin with 270-degree crankshaft, two-valve OHV cylinder heads, fuel injection and gear-driven counterbalancer and makes an estimated 84 rear-wheel horsepower.
There may be hope.

Year/Model: 1975 Norton 850 Commando Mark III
Owner: Jim Gerpheide, San Luis Obispo, California
Words and pictures by Clement Salvadori

(This Retrospective article was published in the August 2012 issue of Rider.)