MARLBOROUGH MUSCLE CARS & BIKES MUSEUM
1973 Norton Commando 750
The Norton Commando was launched by the Norton Motorcycle company in 1967 with OHV parallel-twin 750cc pre-unit engine (transmission not attached to engine crankcase).
The Norton featherbed frame design had been the base of Norton production bikes since the 50s but former Rolls-Royce engineer Stefan Bauer considered the design contradicted all engineering principles and began design on a new frame based around a single 2.25 in top tube.
Bauer set out trying to eliminate vibration problems of parallel twin cylinder engines using 360-degree crankshafts (pistons rising and falling together) that increased exponentially with increases in engine size. The engine, transmission and swingarm were bolted together and isolated from the main frame by rubber-bushed mountings at the front of the crankcase, cylinder head and gearbox cradle. While the system worked well, the bushes had a short life (around 5,000 miles) when road holding thereafter rapidly deteriorated, and the system required constant adjustment that never endeared it to owners or mechanics.
Previous Norton models had the engine mounted vertically but the Commando engine was tilted forward, made easy as the transmission wasn't attached to engine crankcase. The change moved the centre of gravity further forward and made more space behind the carburettors for an airbox.
In 1972 Norton introduced a high compression version of the Commando engine, the Combat. The new engine had tendencies to break pistons and eat main bearings, often after less than 5000 miles. Norton found a fix in the now renowned Superblend bearings, designed like little barrels (as opposed to rollers) and capable of smoothing out crank-flexing/engine wrecking stresses. All '73 engines received new Superblend main bearings but the problematic Combat engine that had created enormous problems for Norton's reputation in 1972 was axed.
The '73 Commando's 750cc engine, fed by twin Amal 32 mm carburettors, was rated at 56bhp with a top speed of 115mph. Power was delivered to the road by means of a 4-speed transmission, 9-plate clutch and chain final drive.
Telescopic forks with internal springs and hydraulically damped take care of the front suspension while the rear has a twin-sided swingarm oil-filled coil-over shocks. Braking is by means of a single 265mm disc with single piston calipers up front and 203mm single-leading-shoe drum on the rear.
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