AJS Stormer. United States. 1969.


27. AJS Stormer / United States


With the advent of the Y4, AJS was certainly ready for the world markets. In the spring of 1969, this beautifully built scrambler had a highly enthusiastic reception in the USA, particularly on the West Coast where a new corporation had been formed to handle both AJS and Norton.

Ever increasing interest was also shown on the continent of Europe. The first Y4 to go to Holland was an outstanding success, in seven events; its Dutch rider took five first places.

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In developing the Y4 prior to production, AJS adopted a policy of testing it in actual competitions, instead of the ‘closed door’ policy employed by many other manufacturers.

In truth, this was following the example of the Stevens brothers who had used a similar formula for introducing their new machines.

There were heartbreaks, mistakes and mechanical failures – all of which occurred in full view of the public.

However, every single failure or breakage was investigated thoroughly.

Peter Inchley and his team were determined that when the Y4 reached production, it would be meticulous, having the built-in reliability factor that has characterised the Ajays of the past.

Simplicity was a feature; the AJS technicians avoided anything in the nature of added complication. Their aim was to build a machine that could be used in event after event without the need for extensive overhauls and tedious stripping down.

Although a power-output of 32 bhp could be made available, Peter Inchley calculated that 27 bhp at 6,400 rpm was ample and would increase the reliability factor, so essential in motocross events.

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High-speed cine-photography and slow motion cameras were employed in order to study the behaviour of suspension units in the most extreme conditions.

These modern scientific methods have resulted in the remarkably efficient and wear-free lightweight ‘Teledraulic’ front forks and Girling suspension units.

Unsprung weight has also been drastically reduced by the adoption of ultra-light AJS hubs and high tensile rims. To ensure absolute reliability in the transmission, AJS engineers have employed an all-metal, diaphragm clutch, similar in design to that fitted on many high-performance race cars.

The drive is taken through a close ratio four-speed gearbox of immensely strong construction. Trouble free ignition is supplied by the energy-transfer system, consisting of a new-pattern coil, matched to an AC generator.

This supplies a hefty spark right through the engine speed range. An Amal concentric type 932 carburettor has been modified specially for the Y4 two-stroke engine.

An air-cleaner is standardised, which actually aids the power unit, as does the scientifically designed exhaust system.

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Detail has been studied, throughout the design. The rear chain is easy and quick to adjust.

Spring loaded footrests are of the folding pattern; the hubs have an ingenious method of excluding dust and water; whilst weight is saved by the adoption of light-alloy mudguards and a two-gallon glass-fibre petrol tank, which is finished in orange.

The seat has been evolved after consultation with the team’s riders and is ideal for high speed, cross-country riding. When one studies the frame, it is realised that this is a masterpiece, of lightweight contruction, possessing immense strength and rigidity.

Built from Reynolds 531 tubing (as used in the Spitfire), which is bronze welded.

The AJS Stormer single-cylinder, two-stroke engine, developed from the original race Starmaker unit, has a compression ratio of 12.3 – 1, and is built entirely from aluminium alloy, both barrel and crankcase being machined to the highest possible engineering standards.

The cylinder is fitted with a spuncast iron liner, to provide longwearing properties. Piston, con rod and flywheels are individually balanced. Exceptionally good breathing characteristics produce excellent torque, particularly in the medium engine speed range. Bore and stroke are of 68 mm, giving a displacement of 247 cc. The engine runs on a mixture of castor-based oil and premium grade gas, in the proportions of 20 – 1.

With a dry weight of only a little over 220 lbs, and a power output of 27 bhp, it’s small wonder that the AJS Stormer is a real flyer.

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AJS Stormer Y40 / Crated for US Market / 1969

The frame provided many important motorcross innovations, the rear shocks were cantered forward and moved forward on the swinging arm, providing greater rear end spring travel; the front forks were leading axle an innovation, again providing longer front fork spring travel; the swinging arm had eccentric adjustment which allowed the chain to be tension adjusted quickly and very simply; the rear axle was fixed, it didn’t need to be used to tension the chain, so the rear wheel was always in alignment: the frames main backbone oval tube with its triangular inner box section was extremely light and incredibly strong, the wheels also had conical hubs to repel mud, stopping it building up.

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