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Dunstall Motorcycles
The History of The Company

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Chapter Three - The End of an Era (1970's)

In the spring of 1970, the Dunstall organisation moved to the Greater London Council's industrial estate at Thamesmead. It was built on reclaimed marshland on the south bank of the river Thames. The range of machine on offer had also changed significantly. The old Atlas based machines were replaced with new Commando based versions. The range now consisted of the Sprint and Export models as before, but also included a Grand Tourer with panniers and bulkier touring fairing. The Tourer had the same engine treatment as the other machines including extensive modification of the head and ports, 1/8-in larger intake valves, high compression pistons, 32mm carburettors and many other refinements. The horsepower was rated at 68 BHP at 7,000 rpm. Also available was a six-speed gearbox with a higher top gear enabling the Dunstall Norton to achieve a top speed of 133 mph.

In the search for a more efficient exhaust system without additional noise, Dunstall worked closely with Dr Gordon Blair of Queens University Belfast, Ireland. The exhaust pipe design (two-into-one-back-into-two) was entirely Dr Blair's while one of Dr Blair's students, Sam Coates, and Paul Dunstall helped to work out the silencer design and dimensions. In addition to the new exhaust, Eddie Robinson developed a new disk brake system. This new system had three improvements over the previous Lister system. The housings, cast interegraly with each fork leg, contained the pads that gripped on stainless steel disks, rigidly attached to the hub rather than floating like the previous unit. Although stainless steel got round the problem of rust on the disk, it did not provide the same braking efficiency.

Dunstall was closely linked to the launch of the Commando. At the launch there were brochures listing custom and conversion or tuning kits. The conversion kits provided three levels of tune and resulted from collaboration with Dunstall. The first stage raised the compression ratio to 10:1 and included a pair of long tapered megaphone shaped silencers to push the speed up to 120 MPH. Stage two brought in a new camshaft, exhaust pipes, inlet tracts and inlet valves to go to 130 MPH. Stage three added a hotter camshaft, racing exhaust system with megaphone, bigger carburettors and a further 7 MPH. All the kits included various other odds and ends, but in the end, none were ever produced.

During 1970, perhaps seeing the beginning of the end, Paul became a dealer for the Honda 750. Doug Mitchenall who was with Avon fairings for a number of years designed the fairing and other glass-fibre components used on the Dunstall Honda. The range offered for the Honda were initially just body parts, but this was later to include a full range of engine parts. Paul also built a prototype Kawasaki 500cc three cylinder two-stroke engined racing machine. The last person to join the Dunstall racing team was Ken Redfern.

Paul withdrew from racing in 1971 because he wanted to concentrate on the development of the new Norton Commando roadster, which was made more difficult because it had to comply with all the US laws. 1971 also saw the launch of the Dunstall Honda CB750-4 Super Sports Roadster. It featured a modified cylinder head, reshaped and polished ports, 10:1 compression ratio, light alloy wheel rims, Dunlop K81 tyres, 3½ -gallon glass-fibre tank, GT dual seat (with locking tail compartment) and 'Ace' style handlebars.

The 1972 model range was quite small. It consisted of a Commando 750 and 810 in a Mk1 (Economy model) and Mk2 (High performance) versions. There was a wide range of Dunstall Honda equipment plus an exhaust system and high compression pistons for the Yamaha 650 XS1 and XS2. One item of interest was the Dunstall Lowboy racing frame assembly. This was based on the original factory lowboy frames, which were acquired when Paul bought the stock of factory Domiracer parts. The frame was designed to accept the Norton 750cc engine, but the 500cc or 650cc engines would also fit. The frame came with braced head stock, gusseted swinging arm pivot. Swinging arm with large diameter pivot bushes for maximum rigidity. It was fully gusseted and incorporated a special spindle adjustment. The frame came with polished dural engine plates to accept the Norton engine and gearbox, a polished chainguard assembly, polished alloy central oil tank, paired Girling suspension units, 3 1/2 gallon tank and lightweight racing seat.

In 1973, Paul started shipping complete bikes direct to dealers in the US. At first this was in kit form, and the local dealer had to assemble the machine. Later in the year, he started shipping complete machines to the dealers. He also created a wide spread dealer network in the US to market the machines and parts. Some 50% of the Dunstall machines went to the States, 20% to Scandinavia, 10% to Australia and the balance split between the home market and other countries. Machines have been exported to such places as the US, Sweden, Australia, and even Vietnam and Guam. The usual method of buying machines from abroad was to travel to the UK, pick up your new machine direct from the Dunstall shop, and then tour the UK or Europe before having your machine shipped back home. It was possible to buy parts abroad, but the cost of buying the parts and fitting them to an existing machine was often more expensive than buying a complete machine direct from Dunstall. At its peak, the company built more than 750 Dunstall Nortons in a single year.

By this time, the Dunstall business was split about half-and-half between Norton and Honda based machines. The 1973 Dunstall Honda 750 featured an exhaust and silencer system designed by Dr Gordon Blair of Queens University, Belfast, and 10.25:1 compression ratio. Other than the exhaust and pistons, the machine was mechanically standard. It did however have a partial fairing with tinted bubble shield, clip-on bars, huge glass-fibre tank and seat. The footrests were set slightly higher and further back. It also had 19" Boranni alloy wheels and Girling shock absorbers. The machine had a 19-tooth countershaft sprocket instead of the standard 18-tooth. The Honda 500-4 that had a very similar list of changes also joined the Honda 750. There was also a range of fairings for the 350, 500 and 750cc Kawasaki machines.

Also in 1973, Kawasaki approached Paul at a bike show in the US and asked if he would produce an exclusive range of custom parts for Kawasaki to sell through their network of 2,000 dealers in the US.

1974 saw the range extended again to include Dunstall Kawasaki and Yamaha machines and equipment. The Kawasaki machines had full factory backing. The Dunstall catalogue had grown so much that it was split into two parts. One part listed the parts he made for a wide range of bikes including Norton, Honda, Triumph, Yamaha, and Kawasaki. The range included conversion kits to produce a Norton 810cc (from a 750 Commando), a Honda 605cc (from a 500-4) a Honda 900cc (from a 750-4), Kawasaki 1100cc (from a 900) and a Triumph 750cc (from a 650). The other catalogue detailed the range of Dunstall machines on offer, which included an 850cc Dunstall Norton based on the new 850cc Commando.

The machines based on the 900cc Kawasaki Z1 were available in a 900cc form, or as an 1100cc expanded version. The Honda 900 produced in the same year had a glass-fibre fairing, and a glass-fibre one-piece seat and tank cover. The stock CB-750 SOHC engine has the cylinders bored by six millimetres for a total displacement of 889cc. The compression ration is raised to 10:1 and the cylinder head is modified with enlarged, reshaped and polished ports. The gear box and clutch are left stock. There is a four into 2-exhaust system feeding a pair of Dunstall Decibel silencers. The wheels are a pair of WM-2 Borrani alloy rims with 4.10 x 19 Dunlop K-81 tires. Girling rear shock absorbers, low level handle bars and rear sets complete the changes.

The 1975 Dunstall Kawasaki 1100cc Z1 followed a similar pattern to all his other Japanese based machines: - glass-fibre fairing, a glass-fibre combined seat and tank cover, lover handlebars, rear sets, 19" Borrani alloy wheels shod with Dunlop K-81 tires. The engine mods consisting of a bored out cylinder block, higher compression pistons (usually 10:1), reshaped and polished head. Some times the front brake was changed (as in this case to a pair of discs), and Girling shock absorbers fitted to the rear.

Around this time, the Dunstall moved into a pair of units in Crabtree Manorway, near Belvedere, Kent. By 1976, Dunstall were offering a tank-cover/seat unit for the Suzuki GT750, GT550 and GT380 machines. A handle bar fairing was also available for the same machines, and a sports fairing was offered for the GT250. It was in 1976 when Paul and Heron Suzuki GB launched a new Suzuki 750 in Texaco Heron Team Suzuki colours. In a complete break with tradition, Paul also offered a sports fairing for the BMW 750 and 900cc models.

The Dunstall involvement with Suzuki began in the 1975 when he customised the GT550 two-stroke triple making it into a suprisingly good and fast bike. Suzuki GB began to think that a link up with Dunstall might be useful. Paul tinkered around with few more two strokes, but by this time two strokes were becoming unfashionable. All this changed with the arrival of the Suzuki four strokes. Paul's first attempt was on the GS550 Four. Before long he went to town on the GS750 and GS1000, achieving with the latter a machine capable of 145 mph. All these machines had the factory backing.

In 1977, the Commando ceased production and Dunstall continued for a few more years producing machines based on imported Japanese machines.

Over the winter of 1978-79 did some more work on the big Suzuki and raised the top speed to 150 mph. The machine was called the GS 1000 CS or Competition Special. It was similar in specification to the other Japanese Dunstalls, but this time things were taken further: larger carburettors with new jets and bellmouth velocity stacks, the new Dunstall Power Silencers, special camshafts, and competition valve springs.


www.woodgate.org/dunstall/chap3.html / Webmaster / Revised 24th February 2000