1972 NORTON COMMANDO
1972 Norton Commando Production Racer.
COMBAT ENGINE
The big news for the 1972 Norton Commando line was the addition of a new, highly-tuned version of the 750 twin, called the Combat engine. Little did anyone know at the time just how bad this engine was or just how trouble it could cause Norton Motorcycles.
MODEL DESIGNATIONS
All four road models became MkIVs & one completely new model was added, the Commando Interstate, meant to be a long-distance touring bike, with a 5-gallon fuel tank.
ENGINE CHANGES FOR ALL MODELS
All models got reinforced crankcase castings with more internal webbing around the main bearings, & a roller race on the timing side to match the drive side main bearing. This meant that crankshaft location was lost & the crank could float back & forth, so shims were needed to control the end play, not a good arrangement. The sump filter was also removed, meaning the scavenge pump was unprotected from debris. They added an inline oil filter on the return line between the engine & gearbox. The timed breather on the end of the cam was eliminated & a breather with separator was installed on the lower back of the crankcase, running to the oil tank.
COMBAT SPELLS TROUBLE
The 1972 Norton Commando came with an option on the Commando Roadsters & the new Commando Interstate for a 'hotter' engine, called the Combat. All Combat engines came with their cases painted black. The advertised extra 5hp came from a bump in compression ratio to 10.0:1 (by shaving the head surface), larger 32mm Amal 932 Concentric carburetors, larger intake tracts to match & a wild high-lift, long-duration cam. The engine proved to be "peaky", with good power in the upper rpm-range, but not so good in the low- & mid-range. So, they geared it down with a smaller front sprocket to help acceleration. This meant it would top out at 108mph at 7,000 rpm, not exactly what you'd expect from a racing engine. This low gearing made it all to possible to over-rev the engine, even in top gear. The pistons, the same slotted versions used since the Norton Atlas, worked fine at 5,000rpm, but at 7,000 under extreme loads, then tended to pull the crowns loose from their skirts.
1972 Norton Commando Roadster LR (Long Range).
MORE COMBAT WOES
In addition to everything else, the cam chains were so awkward to adjust that they rarely were. Since the points were attached to the timing side of the cam, not only would cam timing vary, but so did ignition timing. Add to that a lousy auto-advance mechanism that fluctuated or even jammed. Everything combined conspired to drastically reduce main bearing life to as low as just 4,000 miles, if the rest of the engine lasted that long, that is.
COMBAT MARCHES ON
The Combat engine was coupled with a front disk brake on the Norton options list. Despite all the problems, the Combat engine & disk brake were such a popular item that by mid-year, they were included on every 1972 Norton Commando of every type. Problems & warranty claims went through the roof, badly tarnishing Norton's good name in the eyes of the public. The venerable old front drum brake was dropped from the catalog & only Norton Commando Hi-Riders would have one by 1973. All others had front disk brakes from them on.
1972 Norton Commando Fastback MkIV. Note trademark Fastback tail section & unique tank/seat combo with wraparound knee bolsters.
THE HEART OF THE PROBLEM
The problem, as it turned out, was partly due to the conflict created between the old, flexible crankshaft & the new, more-rigid crankcase. And they took it out on the main bearings, which was exacerbated by the change of the timing side main bearing to a caged roller. As the crank flexed under heavy loads at high rpms, the corners or edges of the rollers were digging into their races.
A SOLUTION
The answer was a self-aligning spherical roller bearing called a Superblend. These had rollers that were slightly barrel-shaped, having softer rounded corners that allowed some flex & didn't dig into the races. New, unslotted pistons were fitted & the auto-advance mechanism was improved. And a larger front sprocket was fitted, raising the gearing such that owners couldn't over-rev their bikes in top gear anymore. But the ultimate solution to the Combat Engine Fiasco was to eliminate the Combat engine. Norton Motorcycles decided that it was more important to focus their resources on their mainstream engines instead, applying what the improvements intended for the Combat to the entire engine line.
1972 A BAD YEAR
Busy doing all that frantic development work & a steady stream of warranty work, very few Norton Commandos were actually available to sell in late 1972. It would not be until 1973 that Norton Commando full-scale production got underway again.
THE JOHN PLAYER CONNECTION
Norton Motorcycles got a nice boost in the form of sponsorship of their racing team by John Player Cigarettes. This had little effect on the problems in the factory at that time, but went a long way toward establishing Norton's prestige even outside the motorcycle industry.
1972 NORTON COMMANDO
Model Designations:
Fastback MkIII
Roadster MkII
Street Scrambler
Fastback LR (Long Range)
Production Racer
Hi-Rider
Interstate
Original List Prices (approx):......................................$1,590
Engine:
Type......................................................................OHV parallel twin
Dislplacement (actual):........................................... 746cc
Bore..................................................................... 73mm / 2.875"
Stroke................................................................... 89mm / 3.503
Compression Ratio:................................................. 9:0:1
Horsepower: ......................................................... 58hp @ 6500rpm
Carburetors ...........................................................(2) 30mm Amal Concentrics
Ignition..................................................................(2) coils
Oil System..............................................................dry sump
Oil Capacity.............................................................6pt.
Lighting System.......................................................12V battery & alternator
Ignition Timing, fully advanced...................................28-degrees BTDC
Primary drive...........................................................triplex chain
Clutch Type............................................................. multi-plate diaphram
Gearbox Ratios:
1st Gear...................................................................12.40:1
2nd Gear................................................................. 8.25:1
3rd Gear.................................................................. 5.90:1
4th Gear.................................................................. 4.84:1
Top Speeds in Gears @ 7000rpm:
1st Gear................................................................... 43.2mph
2nd Gear ................................................................. 64.8mph
3rd Gear ................................................................. 90.6mph
4th Gear ................................................................. 110.4mph
Front Tire................................................................4.10 X 19
Rear Tire.................................................................4.10 X 19
Dimensions:
Wheelbase................................................................ 57.1 inches
Seat Height............................................................... 31.3 inches
Curb Weight.............................................................. 419lb.
SOME BOOKS WORTH LOOKING AT:
MOTORCYCLE REPAIR MANUALS
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Andy
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
1972 Norton Commando
