1972 Norton Commando
1972 Norton Commando Background & History
All four existing road models of the 1972 Norton Commando (ie: Roadster, Fastback, Model S and Hi-Rider) became MkIVs (read that: "Mark Four") and two completely new models were added, the Commando Interstate, and the star-crossed Combat. So, Commando model variants for 1972 had grown to seven different bikes: the Roadster, Fastback, Model S, Hi-Rider, the Production Racer (now in its final year), the new Interstate, and the .
All models got reinforced crankcase castings with more internal webbing around the main bearings, and a roller bearing race on the timing side to match the drive side main bearing. This meant that crankshaft location was lost and the crank could float side-to-side, 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 and gearbox. The timed breather on the end of the cam was eliminated and a breather with separator was installed on the lower back of the crankcase, running to the oil tank.
1972 Norton Commando Roadster
The 1972 Norton Commando Roadster changed little other than the addition of a front disc brake, replacing the excellent 8-inch TLS drum brake. This required a new right-side fork slider to accommodate the caliper mounting. The front disc brake was introduced across all models in the 1972 model year, one year ahead of Triumph. The Roadster was quickly becoming the ‘standard’ Commando, indeed the standard Norton that the public saw most often, and was most familiar with. It didn’t hurt that the Roadster was one of the most attractive motorcycles on the market in 1972.
1972 Norton Commando Interstate
The 1972 Norton Commando Interstate was Norton's entry into the burgeoning motorcycle touring market. Companies like BMW, Honda and of course Harley-Davidson were cashing in on this growing market and Norton wanted, and needed a piece. The Interstate, like most Commando variants, was essentially a stock Commando with a larger 5-gallon (US) fuel tank and an extra-comfy seat. It wasn't a huge seller for Norton, but it helped, and they certainly needed every sale they could get.
1972 Norton Commando Production Racer
Norton was in the habit of spinning off new variants of the evergreen Commando by simply dressing them in different bodywork and trim, while remaining mechanically identical. The Roadster, Model S, Fastback, Interstate, Hi-Rider, and later the JPN (John Playter Norton) were essentially stock Commandos with different appearance packages.
The Production Racer was the exception. PR engines were hand-assembled from hand-picked parts, carefully inspected and matched for weight and clearances, the heads received bigger intake valves and phospor-bronze valve guides along with a squish ring which was machined into the combustion chambers. Rocker arms were lightened and polished, and a hotter race cam was specified. Compression was higher than standard Commandos. They came stock with 32mm Amal Concentric carburetors, however Amal GPs were available as an option. Where the standard Commando produced 58 horsepower, the GP made 68 at a lofty 7,000 RPM.
Because they were so fast, and handled so well, and because they were all painted bright yellow, the Commando Production Racer became known at "The Yellow Peril". A good name considering it dominated several classes of road racing over the years including the Manx TT. While remaining technically street-legal, the PR was truly a factory racer that didn't belong on the streets, although some owners certainly used them this way. Appearance-wise, it was all business. Number plates were molded into the fiberglass rear fender. The sort 'cafe'-style seat with 'bumstop' was fitted along with low, 'clip-on' handlebars and 'rear-set' footpegs and controls. The large PR-only tank was made of aluminum alloy and was very light. There was also an optional half fairing that most of the PRs received. They looked so good that Production Racer Replicas are as common as genuine PRs. If you're shopping for one, make sure you know what you're buying. A well-built PR replica can have a lot of value, especially if you want to ride it. But they'll never be worth as much as the genuine article. So make sure you're paying a price that is in line with that.
The Norton Commando Production Racer remained in production for just three model years, 1970, 1971 and 1972 and, while no accurate records exists, marque experts estimate that between 119 and around 200 PRs were built between all three model years.
1972 Norton Commando Fastback
The 1972 Norton Commando Fastback returned in a wider range of colors. It started the 1972 model year with the tried-and-true 8-inch TLS front drum brake, but finished the year with a front disc brake in its place. The Fastback was meant to be a high-style boulevard cruiser with its quirky 'ducktail' fiberglass rear fender, 'wraparound' seat and tank. There was still a conventional stainless rear fender hiding underneath the tail, to which the license plate was mounted. The ducktail itself was truncated at the back by the tail light, which matched the contour of the tail.
1972 Norton Commando Hi-Rider
The movie “Easy Rider” kicked off the chopper craze of the late-60s and early-70s. Harley had the Super Glide, Triumph had the X-75 Hurricane, so Norton felt it had to follow suit. Unfortunately, their ill-conceived and poorly-executed result was the hideous and totally impractical Commando Hi-Rider. Ridiculous “ape-hanger” handlebars, and that absurd “banana seat” with sissy bar were summarily hung onto stock Commando Roadsters in an attempt to cash in on the chopper craze. Few were sold, and many were converted by dealers back to normal Roadsters before they could find buyers. Many more were converted back to standard bodywork by the owners after the sale. So ironically, today, unmolested, original Hi-Riders are rare and somewhat sought-after by collectors.
1972 Norton Commando 'Combat'
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 much trouble it would cause Norton.
The 1972 Norton Commando came with an option on the Commando Roadsters and 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 and 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- and 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 too 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.
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. The Combat engine was, in fact, in combat with itself.
The Combat engine was coupled with a front disc brake on the Norton options list. Despite all the problems, the Combat engine was a popular option. And the front disc brake was such a popular item that by mid-year, they were included on every 1972 Norton Commando of every type. Problems and 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 and only Norton Commando Hi-Riders would have one by 1973. All others had front disk brakes from then on.
The problem, as it turned out, was partly due to the conflict created between the old, flexible crankshaft and 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.
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 and didn’t dig into the races. New, unslotted pistons were fitted and 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 the improvements intended for the Combat to the entire engine line.
Busy doing all that frantic development work and a steady stream of warranty work (blown Combat engines), 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.
1972 Norton Commando Specifications
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Model designations:
Engine type Displacement Bore & Stroke Compression Carburetors Ignition Engine output Oil system Oil capacity Primary drive Clutch Gearbox Ratios, overall: 1st, bottom 2nd 3rd 4th, top Final drive Frame type Suspension, front Suspension, rear Brake, front Brake, rear Wheelbase Seat height Weight |
Fastback MkIV Interstate Roadster MkIV Street Scrambler Production Racer Hi-Rider Air-cooled OHV parallel twin 746cc / 45 ci 73mm X 89mm / 2.875″ X 3.503″ 9.0:1 2- Amal Concentric, 30mm Battery & coil, Lucas 58 bhp @ 6500 rpm Dry sump 6 pts Triplex chain Multi-plate diaphragm, wet 4-speed constant-mesh, right-foot shift 12.40:1 8.25:1 5.90:1 4.84:1 Chain Double cradle, Isolastic Suspension Telescopic fork, hydraulic damping Swing Arm, 2 dampers, Isolastic mounts 8″ TLS drum, full width 7″ SLS drum, full width 57.1″ 31.3″ 431 lbs |
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