AJS Stormer 500cc Prototype. 1973.


45. Son of Stormer / 1973

The strong, silent, prototype


When Vic Eastwood isn’t hammering around the Grands prix circuits, he’s a development engineer for AJS and the connection between the two ways of life has just appeared in the form of the new works motocrosser.

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This prototype is based quite obviously on the 410 Stormer, but it started life almost by accident. Vic was ‘playing around” with a frame, when he discovered that Graham Evans was also playing around with a big engine up at the Wolverhamton factory.

The two naturally got together, and as the plans went beyond the playing around stage, Martin Jackson was roped in to draft out the new designs and Robin Clews to weld it together. Suddenly Norton Villiers had got them selves a new racer.

The chassis had been modified, as Vic had found necessary to cope with the tough competition. Like on the front forks, where he’s changed the spring rate and damping rate, producing totally new handling characteristics.

Eventually there may also be new leg castings and fork sliders. The original motor was a bored and stroked 410 using a Stormer gearbox.

The unit vibrated and so they decided to use a modified Isolastic set-up pinched from the Commando to isolate the frame. This system was retained even though they eventually ended up with a completely new engine. Vic says that once the swinging arm is set up it will last for two or three meetings without any trouble.

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The motor is a conventional piston-ported two-stroke brought up to 500cc. it drives through a Stormer all-metal clutch and a Norton gearbox. One unusual feature is the type of chain used for the primary drive, where they’ve reverted to an inverted-tooth type.

This was because a triple row chain roller was necessary for reliability, but it was just too wide, and the inverted tooth design was the only way the drive could be made strong enough and compact enough. That is, without completely redesigning the whole transmission and using a gear drive.

They’re not playing around with reed valve induction for the simple reason that “we’ve got more than enough power”. Vic goes on to explain, last year they were getting 47bhp, the new motor gives 39bhp, but it’s quicker. The power starts from tick-over upwards and runs on through the 7,000 peak to 8,000 rpm.

There is so much low-down torque that they don’t need to change the exhaust systems to suit different courses and Vic adds that the motor is more like a four-stroke as far as riding is concerned. The exhaust itself is an interesting point – inside the box is a series of tubes and chambers, which give the expansion box effect, with a silencer in the end.

It results in the required torque characteristics and keeps the noise down to 90dB. In another effort to keep the level of noise down, the decompressor was designed to blow out into the exhaust down pipe. Carburation and ignition are looked after by a large Concentric and a Spanish Femes system. The Amal carburetor is fitted with a redesigned air filter, which again keeps the noise in, while keeping the dirt out.

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The machine bristles with features built in from Vic’s vast experience of the pro motocross, either making for greater reliability or for convenience while working on the machine Vic gave our artist Peter Weller a guided tour around the AJS and the detail sketches he took show just how much thought has gone into the design.

As an indication of the competition, Vic says, “we’re using the brakes more and more as the bikes get faster”, and consequently the Ajay’s brakes have come in for some attention. At the moment this is mainly confined to getting the balance of the brakes set up properly – for example, Vic has spent a lot of time experimenting with the rear brake leverage to get it just right.

When we saw the machine it was weighing in at 104kg, which is reasonably close to the other works machines currently on the GP circus. Vic says he’s got the handling just how he wants it and he’s also got useful power right through the rev range. All that needs to be done is to prove that the machine will stand up to the tough life of international competitions, and the NV will have more than a works prototype.

Will it go into production?

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It’s a bit early to answer that question yet – Vic’s team are still in the last stages of finishing off the factory machine and no definite plans have been made for it at this time. AJS will almost certainly make use of the knowledge and experience gained by racing this machine, however from what Vic says his greatest problems are not mechanical but are mainly concerned with the company’s future.

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