Norton Dominator 99 Model Profile

The 600 cc 99 Dominator was the natural first development step-up from the original Norton twin-cylinder machine, an expanded version of the Bert Hopwood designed 500cc motor that first saw service in 1948 in the plunger-framed Model 7 and later swinging-arm frame under the same model number.

The 500 cc twin was quickly installed in the new Featherbed frame in 1952, to form the original Dominator 88. Initially featuring a bolted-up rear sub-frame, in 1955 this moved to an all-welded frame, then in 1956 the final variant of the Wideline Featherbed frame emerged, to be replaced in 1960 with the Slimline version.

The 99 was launched in 1956, the 600cc twin producing around 36 bhp being formed by lengthening the stroke from 72.6mm to 82mm, and increasing the bore by 2 mm, from 66mm to 68mm. Almost identical in appearance, the two motors can be differentiated by counting the barrel-fins; the 88 features 8 horizontal fins, the 99 has 9!!

1955 had seen the demise of the Model 7, but never one to scrap parts, Norton installed the new 600cc twin engine in the later swinging-arm Model 7 to produce the 77, largely for sidecar use. Interestingly, at the end of the 1950s, a slightly modified frame and suitably altered-for-scramble-use tanks, seats, forks etc produced Norton’s first-ever Desert-Sled, the Nomad, aimed at the by them starting-to-boom US off-road desert-racing scene in first 500cc and then 600cc form.

Many of the components are interchangeable between the 500cc and 600cc engines, camshaft and followers, the timing-chest components, much of the valve-gear etc, even the cylinder heads, thought the smaller engine breathes through a 1” Amal Monobloc carb, rather than the 1 1/16th version on the 600.

First developed with an extremely heavy cast-iron cylinder head with cast-in inlet stub, the head developed through a still cast-iron but separate ally inlet manifold version to an all-aluminium head, all featuring widely-splayed exhaust-ports in search of the avoidance of overheating. In 1960, a slightly different ally-head with more extensive, all horizontal finning joined the new Slimline frame as a further model differentiator, and in 1962 this, with even more splayed exhaust ports and for the first time downdraft inlets manifolds, formed the famous SS head that remained essentially the same right through to the end of Commando production in 1976.

Often accompanying cylinder-head design changes, the cam also evolved over the years, from the initial ‘soft’ cam through the Daytona cam developed for Norton’s racing attempts on the Florida oval in the early 50s, reputedly a rip-off of the Triumph GP cam-profiles, through the ‘quietening-ramps’ late-fifties cam to the SS cam with by now flat cam-followers rather than the previously radiused ones that together with the SS head, brought about a substantial power-hike, to around 40 bhp.

A twin-carb head and the SS cam featured in the run-out model of the 600cc engine, the 1962 99SS (pic 13) , but for model-year 1963 the 99 was defunct, in favour of the full-blown 650 engine to fully match the equivalent BSA, Triumph, Ariel, AJS and Matchless models, the wonderful 650SS. This continued in the model line-up until after the launch of the Commando in November 1967 (pic 17) , in a final incarnation as the rather plain-Jane blue and black painted single-carb Mercury, early 1970 marking the final demise of the famous Featherbed frame after 20 years in production, as the Commando, first in 750 form, then later 850 (actually 828cc) gobbled up the entire production capacity. 1963 also saw the first 750 Atlases produced, for export-only until 1964.

In the meantime, the 500 version continued in 88SS form until being quietly dropped from the range for 1966, with production capacity now concentrated around the 650 and 750 versions of the Dommie engine, the latter with only a few modifications then forming the powerplant of the early 750 Commandos, eventually reaching its final production stretch to 828cc to power the Commando 850 MkI, II and III models. Since then, after-market developers and tuners have produced kits for road and competition bikes taking capacity up in various stages to a full one litre.

Until the 1956 model year, the gearbox fitted was the Norton Lay-Down box (pic 23), a development of an earlier Sturmley-Archer production unit. Norton having been acquired by AMC in 1953, by 1956 the AMC 4-speed gearbox replaced this, largely a development of the same S-A design with a more compact outer cover and gear-change mechanism, but with essentially the same set of cogs and clutch assembly. (pic 20) This AMC gearbox, designed for the mild torque and power-output of 1930s and 40s machines than continued essentially the same, featuring in the entire Norton line-up bar the light-weight Jubilee (250cc), Navigator (350cc) and Electra (400cc) models until the final demise of Commando production in 1978. Even the MkIII 850’s LH gear-change ’box is essentially this same venerable design, though it has to be said that the Commando did bring in a vastly improved diaphragm=spring clutch, and more importantly, properly robust triplex primary-drive in a lovely cast-aluminium casing, whilst the Featherbed models remained restricted to a single-row primary-chain enclosed in a very leak-prone pressed-tin case.

Reverting to the 99, being born in 1956, the 99 immediately benefited from the improved flush-mounted front-brake-plate, all aluminium full-width hub front anchor, and the full-width cast-ally rear hub. With this came the later version of the famous Roadholder forks that, in combination with the immensely rigid Featherbed frame, resulted in handling raised to almost another order of magnitude over almost all the competition, and indeed even Norton’s previous models , which themselves had earned a pretty handy reputation round the bendy stuff.

This big, twin-loop, open box-frame with engine pates bolted in at only 6 points became a natural for Specials builders – there was tons of uninterrupted room there (even for the enormous Vincent V-Twin lump if one was really clever!), and mounting different engines was merely a matter of cutting the appropriate engine-plate, and bingo, Tritons (Triumph-engined), Norbsas (BSA-mills), NorVins (you’ve guessed it!), even Square-4 Ariel Norton specials proliferated.

The development of the later Slimline frame did little to curb this tendency, as the geometry remained essentially the same, with the frame slimming down under the rear of the petrol tank to permit a narrower tank and seat to be fitted to improve rider-comfort (some say!!) and certainly make getting feet onto the ground easier. The sub-frame then widens out again from beneath the rider’s posterior to allow essentially the same swinging arm and rear-shock absorber arrangements as on the previous Wideline-framed machines.

All this resulted in the need to change various cycle-parts. Wideline and Slimline tanks are very different, as are dual-seats, but oil-tanks and battery boxes look essentially the same, though there are details differences that permit the oil tank only to be swapped from Slimline to Wideline, and not vice versa. Mudguards, fork-shrouds, yokes, headlamps etc can be readily interchanged, though the later ‘wide’ yokes were only ever fitted to Slimline models.

Even by modern-bike standards, a well set-up Dommie 99 can be a delight to ride – it’s reasonably powerful if a bit vibe-y, possesses good torque, has a generally nice transmission, stops well enough for its performance, but above all, still sails round the bends!! Yup, that featherbed frame is STILL well up with modern bikes in the cornering stakes, a testament to the wonderful design concept of those two Belfast engineers, the McCandless brothers all the way back in the late 1940s.