Norton 650SS: Norton’s top twin?

Bike Profile

Ross Dickson's 1962 Norton Dominator 650SS.

Story and photos: Jim Scaysbrook • Historic photos: Keith Ward, John Thurgood

In Norton terms, 1962 was the year of the SS. Three separate models were catalogued using the SS moniker: the 500cc 88SS, the 600cc 99SS, and the one everyone wanted, the 650cc 650SS. The smaller two had appeared in the previous year’s line up – the 500 finished in green and dove grey, and the 600 in polychromatic grey and dove grey. 

Of course, the basic twin cylinder design stretched back to the Model 7 Dominator unveiled at the 1948 Earls Court Show as part of the 1949 range. Designed by Bert Hopwood, that engine was to remain in production, with surprisingly few tweaks, until the end of the Commando series nearly three decades later. 

Hopwood’s experience in multi-cylinder engines already included major input on the Ariel Square Four and the ground-breaking Triumph Speed twin, and after his stint at Norton he went on to join BSA where he penned the 650cc A10 twin. However the 650SS, nor any of the big Norton twins, may never have become reality if Hopwood’s intended engineering path for Norton had come to fruition. What he envisaged was a modular range consisting of a 125cc single, a 250cc twin, and a 500cc four, all single overhead camshaft. His presentation to the Norton board included the rationale that Europe, and Germany in particular, had been so utterly destroyed in the war that virtually all post-war production would involve starting from scratch, with new designs embodying the latest technology and thinking. It was folly, he said, to continue to dress up antiquated designs, as was the British way, and the time to make the decision was right now. 

The one flaw in Hopwood’s play was how the radical new modular range would be funded. Simple, he said – scrap, or suspend, the works racing program. That suggestion brought him into deadly conflict with the outspoken head of the Norton racing Department, Joe Craig. It was a showdown where there would be only one winner, and it wasn’t Hopwood, who was shown the door, and immediately welcomed by BSA. Norton continued with their enormously expensive and ultimately futile racing program, until the cash finally ran out in the mid ‘fifties.

Main: Former Australian Short Circuit Champion Vince Tierney on Barry Ryan’s 650SS at Darley in 1962. Inset: Brochure from 1963 shows the 650SS without the optional rev counter.

Twin time

Hopwood’s modular plan was quickly forgotten, and in its place came Norton’s answer to the current British parallel twin craze in the shape of the Model 7 – another 360-degree design with twin spark magneto, with bore and stroke of 66mm x 72.6mm. His experience at Triumph had shown that the Speed Twin suffered from cylinder head overheating, and to overcome this Hopwood’s Model 7 featured a splayed design for the valve gear, giving improved air flow between the inlet and exhaust valve ports. He had wanted to use a single-piece crankshaft, but this was quickly rejected on costs grounds, forcing him to use a three-piece built-up design like the Triumph, with a cast iron central flywheel. Subtle modifications needed to be built into this structure to avoid infringing the Triumph patents. A chain driven single camshaft at the front of the engine operated the valve gear, unlike most other British twins of the time which used separate camshafts front and rear. The BSA design used a single camshaft, gear driven from behind the engine. On the Norton original design, a single inlet manifold branched within the head casting to feed the inlet valves, but this was soon changed to separate ports running into parallel inlet tracts.

As laughable as it seems now, the new twin was tested on an ancient dynamometer that was so completely worn out that torrents of water and oil gushed out of it and across the factory floor and into the street, where pedestrians were forced to wade through the mess. After police threatened action, the solution was to post a worker on the footpath with a large broom to sweep the overflow into the gutter, from where it simply washed into the storm water system and eventually into the River Tame. Ironically, the factory contained new and sophisticated dynos, but these were locked away for the exclusive use of the racing department. The old dyno gave inconsistent and wildly inaccurate readings, and as a result, the new twin was found to be short on power in prototype form. 

Allan Osborne in the Production Race at Darley in 1962. His 650SS is fitted with Siamezed exhaust pipes.

With dealers clamouring for supplies of the Model 7 following its Earls Court debut, production was delayed while Craig was given the task of extracting more power, although none of his ideas were incorporated in the final design. At this point, Norton was teetering on the verge of bankruptcy, and cuts to the workforce and in supplies were being done on a weekly basis. Now effectively barred from the development of the twin, Hopwood resigned, although the board stated that he had been dismissed as part of the economy drive. Just weeks later the first production Dominators finally appeared, and when the first reports by journalist road testers came back, the praise was universal. Most of the initial production was earmarked for export, and the model remained unchanged until 1952, when the plunger frame (derived from the ES2 single) gave way to a swinging arm frame, although not of the fabled ‘Featherbed’ design. In fact, the frame used the single front down-tube ‘diamond’ from the ES2, with the new rear suspension. 

Around this time, a Featherbed frame version of the twin, called the Model 88 was also announced, but initially for export only. Unlike the frame used on the race bikes, the twin’s frame was made from mild steel, with the swinging arm pivoting on Silentbloc bushes and controlled by Armstrong units. The next major change in the twin’s history came in 1955 with the introduction of a 596cc model, with engine dimensions of 68mm x 82mm, called the Model 99. Apart from a larger carburettor and a warmed up camshaft, the 99 was identical to the 88. 

Detail changes were made as Norton dragged itself through the ‘fifties, the most noticeable (to the horror of the traditionalists) being the replacement of the magneto and dynamo with coil ignition and a Lucas alternator. A single ignition coil supplied sparks to a distributor which incorporated the points, condenser and automatic advance unit. 

John Thurgood’s brand new 650SS, prior to its Bathurst debut.

To titillate the American market, a twin carburettor 600, called the Nomad, was introduced in 1958, using the earlier swinging arm frame. This created an immediate demand for a twin-carb home market version, and Norton responded with special 88 and 99 models fitted with double Amal Monoblocs on a splayed manifold. Both the carbs were the same size as used on the single-carb versions, and later models incorporated high compression pistons. 

It had been obvious for some time that the next logical step was to join its competitors in offering a 650, and in November 1960 this became a reality at the Earls Court Show with the announcement of the Manxman – a name insisted upon by Norton’s US distributor. At 646cc, the capacity had been enlarged by lengthening the stroke from 82mm to 89mm while retaining the 68mm bore.  New crankcases were necessary to take the longer stroke, with a wider flywheel and larger diameter crankpins. The light alloy downdraught cylinder head was derived from the 500cc Domiracer ridden to third place in the 1961 Senior TT by Australian Tom Phillis, with wide-splayed exhaust ports and parallel inlet tracts. Compression ratio was 8.3:1 with a pair of Monoblocs mounted on a downdraft manifold. A rev-counter was standard fitment, driven from a coupling on the timing chest linked to the camshaft sprocket. The Manxman was very much US-aimed, with high, wide handlebars, chrome plated, valanced mudguards and a polychromatic blue finish. Early in 1961, another version of the Manxman appeared at the Amsterdam Show, featuring more European styling and with the tachometer mounted on a bracket separate from the headlight shell. In April the same year, Norton announced SS versions of both the 500cc and 600cc Dominators. 

The SS (Sports Special) models featured twin carburettors, bigger and polished inlet ports, multi-rate valve springs, tapered hollow light alloy pushrods, and the sports camshaft from the Manxman.  To cope with the extra power, both models had higher overall gearing and used a Siamesed exhaust system. The sporty nature was enhanced with flat handlebars, ball-end levers, and a folding kickstarter. Rear-set footrests and gear lever were optional extras, designed for the emerging Production Racing classes. Several British magazines tested the 99SS and achieved top speeds around 108 mph (174 km/h). To the delight of the café racers, the Manxman became available late in the year in three versions; standard, de-luxe and SS. 

John Thurgood takes Murray’s Corner at Bathurst in 1965.

Enter the 650SS

Then for 1962 came the formalisation of the Norton twin range with all three capacities available in three specifications. Top of the line was the 650SS, with twin 1 1/16” Monobloc carburettors, developing 49 bhp at 6,800 rpm. The clutch was beefed up with an extra plate and a twin exhaust system was standard, although the Siamesed type was listed as an option. The 650SS came with a magneto and alternator, with coil and alternator on the other two 650 models. To be eligible for British Production racing, Norton catalogued rear-set footrests, brake and gear lever as optional extras.  Within weeks of its release, a 650SS ridden by Phil Read and Brian Setchell won the Silverstone 100 kilometre race, and soon after the same pairing added victory in the Thruxton 500 Mile race.

The British press fell upon the new models and soon reports of top speeds approaching 110 mph were filtering back. If there was a complaint it was that when flooded, the downdraught carbs allowed fuel to run down the inlet ports and straight into the engine, making starting difficult. The 650 models were so popular that the 600s were dropped from the range in 1963 – the year that Norton finally moved out of its traditional home in Bracebridge Street, Birmingham and took up residence within the AMC factory in London. The last Nortons to be built at Birmingham was a batch of 85 650SS models ordered by the Queensland Police.

“I regard the SS as one of the most desirable and rideable classics available,” says Ross.

It was the beginning of a confusing time, not just for Norton but for its AJS and Matchless siblings, with parts shared between models and the gradual identity loss of all three once-great brands. The 650SS standardised in traditional black frame with silver fuel tank and the very ‘sixties chrome tank panel incorporating abbreviated knee pads, and continued in this form until its demise in 1967. As Norton went full-steam on the Commando model, launched in 1967, the only 650 that remained in production, existing mainly on accumulated component stocks, was the Mercury, which could be had in a variety of options, according to what was available. 

Track time

Out in the Colonies, the 650SS found immediate favour with the sporting set, as production racing was becoming increasingly popular and competitive. In Sydney, Parramatta dealer Barry Ryan secured one and put leading dirt track rider Vince Tierney on it in time for the Easter 1962 Bathurst meeting. The Bathurst promoters, always traditionalist, had bowed to pressure and squeezed a combined Lightweight and Unlimited Production Race into the already crowded program for the NSW Grand Prix. The larger class drew 32 starters and after recording 132 mph (211 km/h) on Conrod Straight in practice, few would have bet against Jack Forrest’s BMW R69S. But the BMW at first refused to fire from the dead-engine start, and Tierney bolted away to win by 20 seconds from the fast-closing Forrest. 

Although the speedo stayed in the headlight shell along with the ammeter and headlight switch, tacho had a separate mount.

In June of the same year, Tierney and the 650SS ventured south to the tight Darley circuit near Bacchus Marsh, where the Production Race, of 30 minutes duration, was a highlight of the program. As well as renewing his rivalry with Forrest’s BMW, he had local star Allan Osborne, also on a 650SS, to deal with. For 21 torrid laps, Tierney and Osborne staged a monumental battle for the lead and with the 30 minute time limit just seconds away, both riders began what was believed to be their last lap. Around the back of the circuit, Tierney collided with a lapped rider on a 250, bringing them both down, while in avoiding the melee, Osborne was forced off the circuit and into the scrub. All were unable to restart and veteran Forrest, having his last race and nearly a lap behind, was shown the chequered flag. This result was soon scrapped by the timekeeper, Bob Payne, who claimed under the race regulations that, “when the 30-minute race distance expired, both Norton riders had covered the most laps.”  Forrest vigorously protested the decision but was not successful. 

Twin Amal Concentric carbs breath through Atlas air filter.

The following year at Bathurst, John Thurgood led a 650SS clean sweep of the top placings in the Unlimited Production. In 1964, Thurgood’s 650 was narrowly beaten for top honours in the same event only by Kel Carruthers’ 750cc Norton Atlas – a result that saw A Grade riders on trade-entered machines banned from production races. Thurgood made amends to win again at Bathurst in 1965 on his now four-year-old 650SS. “All I did to it was to polish the bottom end,” says John, “but that had quite a difference. In that race with Kel there was no difference in top speed, he just had more grunt up the mountain but I stayed with him down the straight and passed him under brakes at one stage.”

So, why all the fuss?

Mention Featherbed twins and invariably, the 650SS is claimed to be the pick of the bunch. Perhaps it’s because in terms of outright top speed, it could match the 750 Atlas, although the mid-range torque was not as strong, but where as the Atlas was infamous for its vibration, the 650SS was, in comparison, as smooth as silk. And of course, it handled impeccably, thanks to the legendary Featherbed frame (now in so-called ‘Slimline’ form) and the proven Roadholder forks. The 650SS was certainly on the wish list for Ross Dickson, from Melbourne, so when a fully-restored 1965 model came up for sale at Classic Style in Seaford in May 2003, he grabbed it.

“I regard the SS as one of the most desirable and rideable classics available,” says Ross. “Since I’ve owned the bike I have done about 20,000 miles, and like all things old and British, many things have either been replaced or upgraded. Not long after purchasing the bike I had to replace the head gasket. Returning from Phillip Island in 2009 I melted and cracked both pistons. I believe this was a combination of two things: the faulty magneto and the single carb manifold which could have been sucking air. The bike actually came with twin Monoblocs but I had issues keeping the two synchronised, so I purchased a new single manifold from UK. The manifold was a very poor design, having only two bolts located on the outside to attach it to the cylinder head. 

Man and machine. Ross Dickson reckons he now has his 650SS just how it should be.

I rebuilt the top end of the motor and magneto, and fitted a pair of Concentrics instead of the single Monobloc (Concentrics were fitted standard in 1967, the model’s final year). The Concentrics were pre-jetted by Mick Hemmings to suit this motor and turned out to be very close to the correct settings. The slightly larger (30mm) carbs required the manifolds and ports to be opened out slightly to match.  I bought new header pipes from England which didn’t fit, so I had new pipes made locally. I have added an Atlas air filter, a Commando-style oil filter, and a twin leading shoe front brake plate. 

Everything was going fine until coming home from Yea I could hear a rumbling sound, which Greg Fitzpatrick immediately identified as main bearings. These were replaced with FAG Superblends and the crankshaft ground. To prevent oil entering the combustion chamber, the one-piece oil rings were upgraded to the segmental type and valve stem seals were fitted on both inlet and exhaust. Someone had drilled out the oil jet holes in the conrods to a much larger size than required, so these were epoxied up and redrilled to the correct angle as original with the aid of a jig. The distributor was replaced with a Mick Hemmings magneto replacement kit and to give a stronger spark I installed a Boyer ignition system. The bike performs very well and the note emitted from the mufflers is markedly improved. 

Rubber bung in chaincase is removed for strobe light timing.

I have always thought that it would be a good idea to put the 650SS on a dyno to ensure everything is set up correctly, and my mate Craig who did the rebuild knew of a mob in Ringwood (Intune Motorcycles) who had recently done two Manxes. Good enough for me, I thought. The result was a reading of 33 horsepower at the rear wheel, and they explained that you lose 20% of the power by the rear wheel. It is running a little lean at low speed and a wee bit rich at high revs, so we need to raise the needles one notch and fit one size smaller main jet. Once that is done I will return to the dyno to check everything is set up correctly.

A friend of mine who is an absolute genius when it comes to Nortons maintains the bike. It is not concours as it does get ridden and gets stone chips and scratches, but it has done me proud by winning several club trophies. It’s amazing how many people, when I pull up at a service station, come and check it out”. 

Specifications: 1962 Norton Dominator 650SS

Engine: Parallel twin cylinder, overhead valve. Crankshaft in ball and roller bearings, plain big end bearings. 
Bore x stroke: 68mm x 89mm. 647cc.
Carburettors: Two Amal Monobloc 1 1/16” choke.
Ignition: Lucas magneto
Electrical: Lucas RM19 alternator, 6v 13 amp-hour battery with rectifier.
Transmission: AMC 4 speed gearbox. Chain primary and final drive.
Fuel capacity: 3.5 gallons (16 litres)
Wheels: Norton full width hubs, 8 inch diameter front, 7 inch rear19 inch steel rims.
Tyres: 3.00 x 19 front, 3.50 x 19 rear.
Suspension: Norton Roadholder front forks, Girling rear units.
Weight with fuel and oil: 434 lb (197 kg)

This article first appeared in Old Bike Australasia Issue 58.