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Remembering the 1951 AJS Model 20 500

1951 AJS Model 20 500

The AJS Model 20 was a British motorcycle made by Associate Motorcycles between 1948 and 1958. Until 1949, the model was mainly exported to the United States. However, from 1949 onwards, the AJS model was sold to the British. The 1949 model had megaphone silencers, a dual seat, and an engine enclosed in a pivoted fork frame with telescopic front forks. When the company introduced the 1951 AJS Model 20 500 motorcycles, they included a horn-push on the handlebar, the Jampot unit for its rear suspension, and a medallion badge. To further understand this vintage motorcycle, here are five features that made it unique in that era.


The motorcycle uses a magneto ignition system to generate energy. A magneto is a generator that produces electricity to power the motorcycle. The magneto produces a voltage when the engine rotates it. To produce more voltage, the rotation needs to be high. Instead of a separate coil, the magneto has both primary and secondary windings that aid in boosting the voltage. The advantage of the magneto ignition system is that you do not need to charge it since it has no battery. A magneto usually generates high voltage power at once. That means some of the unused energy will be stored. Also, with no battery, repair and maintenance costs became cheap. Batteries frequently malfunction, which means most of your money will be spent on them.


This motorcycle uses a wet multi-plate clutch. A multi-plate clutch contains a series of clutch plates, unlike a single plate clutch with one clutch. More clutches mean more friction surfaces. Friction surfaces are crucial for torque. Multi-plate clutches, therefore, have higher torque than single plate clutches. With high torque, the motorcyclist can quickly overtake another vehicle. When overtaking another vehicle, you need more power to take off. If you took off with low power due to insufficient torque, you are likely to collide with another vehicle in the other lane. Its high torque also enables the motorcyclist to swerve quickly to avoid any oncoming danger. For instance, if you are about to hit a tree, you need enough power to turn away to avoid it. In a single plate clutch system, you would likely turn too slow and collide with the tree. Also, a wet multi-plate clutch system decreases the effort the rider needs to press the clutch pedal. With more clutches, the motorcycle develops high power. As a result, you will not have to use a lot of your energy to step harder on the clutch.

Motorcycle Type

The motorbike is an all-round one. All-round motorcycles typically emphasize performance than comfort. The motorbike has good braking, powerful acceleration, high speed, and can move around rocky terrains. Compared to most motorcycles, this motorcycle is generally lighter. This is because the manufacturers use aluminum and other light materials to achieve the lightweight. With a light motorcycle, you can take off at high speed, swerve quickly and move up a hill. If the motorcycle were heavy, you would struggle to move faster with it since you would need to apply more effort to get it to move. Also, the motorcycle has narrow and hard seats. Its seat arrangement allows you to rest your feet at the rear as you ride. To ride this motorcycle, you have to lean forward to reduce aerodynamic drag. Aerodynamic drag will suck you out of your bike if you lean backward.


The motorcycle has spoked wheels. Even with the evolution of other motorcycle parts from the 1940s, spoked wheels remain popular today. Manufacturers prefer spoked wheels because they use steel which is cheaper than most metals. Riders also like spoke wheels but for different reasons. The motorcycle's spoked wheels make it ideal for rough terrains. For instance, when you ride along rocky paths, there is a chance your wheels could hit rocks. Fortunately, the rocks will not damage the rods in the wheels. Instead, the rods will bend and flex to a certain degree to accommodate the force of the rocks. This means the rods will not snap or come off. Even if the rods somehow came out, the cost of repairing them is low. For instance, you will only replace the affected rods rather than the entire wheel. If one rod is damaged, you will buy one rod.

Cooling System

This motorcycle uses an air-cooled engine. The motorcycle has fins on the outside to trap air to cool the engine. The fins have a large surface area which allows air to pass over them. As cool air passes over them, they also draw heat away from the engine. Generally, air-cooled engines do not require a radiator, coolant and cooling jackets. These three components would otherwise make this motorcycle heavy, and it would not be ideal for rough terrains. Another benefit of the absence of the parts is that the maintenance and repair costs are cheap. For instance, you will not need to visit a garage to replace a radiator, as you would with a liquid-cooled engine. Since it does not require a coolant, you do not run the risk of a leaky coolant. The engine will not be thoroughly cooled with a leaked coolant since some of it will be wasted. Another danger is that coolant can freeze in the engine. With the freezing taking place, the engine will need to generate a lot of power to run the engine. Sometimes, the engine may be unable to run, and it will break down.


Although the 1951 AJS Model 20 500 bike is no longer popular, it did change how manufacturers made their motorbikes. For instance, the spoked wheels continue to be popular today. Even though they serve beneficial uses, some riders admire the spoked wheels for their design. The spoked wheels follow a certain geographical pattern, which most people find visually appealing. Also, the makers of this motorcycle popularized the use of all-round motorcycles. Before the 1940s, manufacturers would only manufacture motorbikes for specific terrains. Such a move was inconvenient since it meant that a motorcyclist would have to purchase motorcycles for different terrains. Fortunately, with this motorbike, bikers could finally travel anywhere.

Benjamin Smith

Written by Benjamin Smith

Benjamin Smith is one of the managing editors of Moneyinc. Ben's been focusing on the auto and motorcycle sector since 2005. He's written over 1000 articles in the space and continues to learn about it each day. His favorite car is "any Bugatti" and he's a die hard Harley Davidson fan.

Read more posts by Benjamin Smith

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