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Introduction to the AJS Porcupine

The AJS Porcupine is a motorcycle that emerged in the early 1950s, designed and manufactured by the AJS
Motorcycles brand, which was a renowned British motorcycle manufacturer. The AJS Porcupine was not just any
ordinary motorcycle; it was a technological marvel of its time, with many features that set it apart from its
contemporaries. The name "Porcupine" itself was a nod to the bike's distinctive spiked fins on the cylinders, which gave
it an aesthetic similar to the prickly quills of a porcupine.

The Porcupine's technical achievements were significant, and it was widely regarded as one of the most advanced
motorcycles of its era. With a 500cc parallel-twin engine, it was designed to compete in the prestigious Motorcycle
Grand Prix, where it was intended to challenge the best in the world. The Porcupine earned a reputation for its unique
design and impressive performance, making it one of the most iconic motorcycles in the history of British racing.

were both fast and reliable, a was not only fast but also reliable
reputation that would be tested and easy to maintain.
when the Porcupine was introduced.
One of the most significant design
The Need for a Competitive Edge choices made during the
development of the AJS Porcupine
By the late 1940s, motorcycle
racing had become increasingly was the parallel-twin engine
competitive, and manufacturers configuration. At the time, most
were in a race to develop the most racing motorcycles were powered
advanced and powerful racing by single-cylinder engines.
motorcycles. The 500cc class in However, AJS believed that a
p a r t i c u l a r h a d b e c o m e a parallel-twin engine would provide
battleground for the world's best better balance and reduced
motorcycle manufacturers, with vibration, allowing the bike to
many pursuing advancements in handle more effectively at high
engine technology, aerodynamics, speeds. The parallel-twin engine
and handling. AJS, known for its also offered more power and
precision engineering, saw an torque, which was crucial for
opportunity to break away from the competitive racing.
The Historical Context of the AJS competition by introducing a truly The engine's displacement was set
Porcupine innovative machine: the AJS at 500cc, which was the standard
Porcupine. for the premier racing class.
The Rise of British Motorcycle However, it was the details of the
Brands At the time, single-cylinder engine that made it truly unique.
engines were dominant in the 500cc
In the early 20th century, the British racing class. However, AJS's The engine featured an innovative
motorcycle industry was a dominant decision to develop a parallel-twin dual overhead cam (DOHC)
force in the world, with companies engine was a bold move, setting the design, which allowed for greater
like Norton, BSA, and Triumph Porcupine apart from other bikes on power output and more precise
leading the charge. British the grid. This choice marked the control over the engine's
motorcycles were known for their beginning of the Porcupine's story performance. The cylinder heads
durability, engineering excellence, and its eventual role in one of the were designed with large, finned
and innovation. As the popularity of most legendary chapters in the areas to improve cooling, and the
m o t o r c y c l e r a c i n g g r e w, history of motorcycle racing. engine cases were crafted from
manufacturers began developing lightweight materials to reduce
specialized racing machines, with a The Development of the AJS weight and improve handling.
focus on speed, handling, and Porcupine Engineering Challenges
advanced technologies.
Design Philosophy Building the AJS Porcupine was
The AJS brand, founded in 1909 by The development of the AJS not without its challenges. The
the Collier brothers (Harry and Porcupine was spearheaded by parallel-twin engine configuration
Louis Collier), quickly established Leslie Graham, AJS's chief itself was relatively new for racing
itself as a major player in the designer and engineer. Graham had motorcycles, and much
motorcycle industry. Known for its a background in automotive experimentation was required to
engineering p recis io n an d engineering and a deep perfect the design. AJS engineers
innovative designs, AJS was one of understanding of the challenges worked tirelessly to fine-tune the
the first manufacturers to develop involved in developing a engine, balancing power output,
successful racing motorcycles, with competitive racing motorcycle. weight distribution, and reliability.
a strong presence in various racing The design philosophy behind the
disciplines. The brand's success was Porcupine was to create a bike that One of the key challenges was
built on producing machines that ensuring the engine's longevity and

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LHR Motorcycle Magazine Issue 12 April 2025