Motorcycle engine
From Wikipedia, the free encyclopedia
A motorcycle engine is an engine found in a motorcycle, which serves to propel the motorcycle. The motor typically sits immediately under the fuel tank, in between and just forward of the rider's legs.
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[edit] Types of Engine
Almost all commercially available motorcycles are driven by conventional gasoline internal combustion engines, but some small scooter-type models use an electric motor.
Gasoline engines can be compared by many criteria.
[edit] Displacement
Displacement is defined as the total volume of air/fuel mixture an engine can draw in during one complete engine cycle. In a piston engine, this is the volume that is swept as the pistons are moved from top dead center to bottom dead center. To the layperson this is the "size" of the engine. Motorcycle engines range from 50 cc (cubic centimetres) to 2300 cc.
[edit] Number of cylinders
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.
[edit] Single cylinder
One-cylinder motorcycles are known as "singles," and "thumpers" (for the sound they make). In most singles, the cylinder points up and slightly forward, spark plug on top. They are most common in off-road and dual-purpose motorcycles, though there are some cruisers and small-displacement sport-bikes that use single-cylinder engines.
[edit] Two cylinders
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 motorcyles and Japanese motorcycles, is the inline twin also known as the parallel twin. In this design the cylinders are side by side vertically above the crankcase. If not vertical they are generally close to in order to maximise airflow cooling.
The angle in the V-twins varies from around 45 degrees to 90 degrees. Typical of the former is the Harley-Davidson and Vincent engines which due to their firing order tend to vibrate more. Ducati and Moto Guzzi make V-twins cylinders at s 90 degree angles to quell primary vibrations. Moto guzzi motorcyles have had their engines crosswise in the frame one cylinder to the left, one to the right.
The parallel twin engine configuration was made famous by Edward Turners Triumph Speed Twin design as used on the Triumph Bonneville. BMW makes their famous flat-twin ("boxer twin")engine where the cylinders are horizontally opposed, protruding from either side of the frame. The boxer is the only twin-cylinder arrangement that is inherently balanced, producing very low vibration levels without the use of counterbalance shafts. Sunbeam produced a water cooled inline twin driving a propshaft.
Narrow-angle V-twin engines dominate the cruiser motorcycle segment.
[edit] Three cylinders
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 are two of the motorcycle manufactures using triples in their large displacement motorcycles.
On the other hand, in a two-stroke world triples were more common. In the 70's Kawasaki had its 250, 350 500 and 750 triples which were known for their power (but maybe not rideability) and Suzuki had 380, 550 and 750 triples of which the last one was water cooled and thus gained the nick name "Water Buffalo". All the others above were air cooled.
[edit] Four cylinders
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 unusal 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.
Since the advent of Honda's CB750 straight-four engine, straight-fours have dominated the non-cruiser street motorcycle segments.
[edit] Five cylinders
Honda has produced a five-cylinder engine for racing, the RCV, but no five-cylinders exist for commercial production motorcycles.
[edit] Six cylinders
Six cylinder engines are uncommon, and found only on the biggest motorcycles. One of the best six cylinder examples is the Kawasaki Z1300. Nowadays the most famous six cylinder engine is the boxer used on the Honda Valkyrie series and Honda Gold Wing.
[edit] More than six cylinders
A number of custom and one-off motorcycles use more than six cylinders. For example, the Boss Hoss motorcycle uses a Chevy V-8 motor. But no major motorcycle manufaturer uses more than six cylinders.
[edit] Cooling: Water, Air or Oil
[edit] Water
Water-cooled motorcycles have a radiator (exactly like the radiator on a car) which is the primary way their heat is dispersed. Water is constantly circulated between this radiator and the cylinders when the engine is running. The radiator has a small fan attached to it which is controlled by a thermostat. The cooling effect of this fan is enough to prevent the engine overheating in most conditions, thus water-cooled bikes are safe to use in a city, where traffic may frequently be at a standstill.
Emissions regulations and the market demand for maximum power are driving the motorcycle industry to water-cooling for most motorcycles. Even Harley-Davidson, a strong advocate of air-cooled motors has begun producing the Revolution water-cooled engine.
[edit] Air
Air-cooled motorcycles have no "cooling system," as such. As air blows past the engine case, it disperses heat. The cylinders on these bikes are designed with heat sinks (fins) to aid in this process. Air cooled bikes are cheaper, simpler and lighter than their water-cooled counterparts, but unless the ambient temperature is cold, they may overheat if the bike stands still, as in traffic.
[edit] Oil
Some manufacturers use a hybrid cooling method where engine oil is circulated between the engine case and a small radiator. Here the oil doubles as cooling liquid, hence the name "oil-cooling." Suzuki has produced many "oil-cooled" motorcycles.
[edit] Four stroke or Two stroke
As applied to motorcycles, two stroke engines have some advantages over equivalent four-strokes: they are lighter, mechanically much simpler, and produce more power when operating at their best. But four-strokes are cleaner, more reliable, and deliver power over a much broader range of engine speeds. They use the 'Otto cycle': Induction-Compression-Power-Exhaust. In developed countries, two-stroke road-bikes are rare, because - in addition to the reasons above - modifying them to meet contemporary emissions standards is prohibitively expensive. Almost all modern two-strokes are single-cylinder, air-cooled, and under 600 cc.
In Europe there are a lot of water cooled 125 cc two-strokes and offroad motorcycles that are also two-strokes with water-cooling.
[edit] Other components
Fuel injection and computer engine management systems are now usual on large and expensive bikes, and starting to propagate to smaller bikes, driven by increased demands for emission control and improved performance. Capacitor Discharge Ignition (CDI) is now standard on all bikes, as opposed to the previous technology, magnetos.
