Motorcycle Engines

Motorcycles have mostly, but not exclusively, been produced with one to four cylinders, and designers have tried every imaginable layout. Engines with more cylinders provide more power for the same displacement, and feel smoother to ride. Engines with fewer cylinders are cheaper, lighter and easier to maintain.

One-cylinder motorcycles are known as "singles," and in larger capacities as "thumpers" (for the sound they make). In some singles, the cylinder points up and slightly forward, spark plug on top but the most common arrangement is a horizontal cylinder such as used by Honda in its C series singles, the highest volume motorcycle of all time with over 40 million units. They are most common in all configurations..

Two-cylinder motorcycles are called "twins." The two most common arrangements are

the "V-twin" where the cylinders form a "V" around the crankshaft, which is oriented transversely (i.e., perpendicular to the direction of travel).
also common especially in classic British motorcycles and Japanese motorcycles, is the inline twin or straight-two, known as a parallel twin when the cylinders share a common crank pin. In this design the cylinders are side by side vertically above the crankcase. If not vertical they are generally nearly so in order to maximize airflow cooling.

BMW's famous opposed twin - The angle in the V-twins varies from around 45 degrees to 90 degrees. Typical of the former are the Harley-Davidson and Vincent engines which due to their firing order tend to vibrate more. Ducati and Moto Guzzi make V-twins with cylinders arranged at a 90 degree angle to quell primary vibrations. Some Moto Guzzi motorcycles have V-twins oriented transversely: one cylinder to the left, one to the right.

The parallel twin engine configuration was made famous by Edward Turner's Triumph Speed Twin design as used on the Triumph Bonneville. In the famous BMW flat-twin ("boxer twin") engine, the cylinders are horizontally opposed, protruding from either side of the frame. The boxer is the only twin-cylinder arrangement that has inherent primary balance without a rocking couple, producing very low vibration levels without the use of counterbalance shafts. Narrow angle V twins vibrate. Sunbeam produced an air cooled inline twin driving a prop shaft.

Narrow-angle V-twin engines dominate the cruiser motorcycle segment.

Three-cylinder designs are unusual — they are referred to as "triples" and are normally inline triples in layout. The British Hinkley built Triumph and Italian Benelli as well as Japanese Yamaha are three motorcycle manufacturers who have used triples in their large displacement motorcycles. The Italian firm Laverda was also renowned for their 1000cc and 1200cc triples.

On the other hand, in the two-stroke world, triples were more common. In the 1970s Kawasaki had its 250, 350, 500, and 750 triples which were known for their power (but maybe not ride ability) and Suzuki had 380, 550, and 750 triples of which the last one was water cooled and thus gained the nickname "Water Buffalo" or "Kettle". All the others were air cooled. Honda also produced a water cooled V-3 two-stroke.

Four-cylinder engines are colloquially known as "four-bangers." They are quite similar to car engines, and most commonly have a transverse-mounted inline four layout, although some are longitudinal (as in the earlier BMW K series). V-4 and boxer designs (as in the Honda Gold Wing series) have been produced.

One of the more unusual designs was the Ariel Square Four, effectively two parallel-twin engines one in front of the other in a common crankcase - it had remarkably little vibration due to the contra-rotating crankshafts. Yamaha and Suzuki used the same concept in their water-cooled two-stroke engines (RZ500 and RG500 respectively).

Since the advent of Honda's CB750 straight-four engine, straight-fours have dominated the non-cruiser street motorcycle segments.

Engines