The working mechanism of a motorcycle engine is similar to that of a car or bus engines. But different motorcycle engine types have a different working mechanism in comparison to stroke, power output and balancing.
- Types of motorcycle engines made till now (some rare one is not covered)
- How do motorcycle engines work?
- How difficult it is for engineers to balance the motorcycle engine and how it affects the balancing of a motorcycle.
Most of the motorcycle engines till now are Internal Combustion engines as electric motorcycles are also coming in the market. It consists of the Spark plug, Valves, Piston, Cylinder, Piston Rings, Connecting rod, Crankshaft, sump, etc.
According to some automobile magazines, the automobile industry is shifting toward electric or other hybrid engines so maybe in near 4-8 years we will hardly see any I.C. engines powered motorcycle.
The motorcycle engines are basically of two types two-stroke and four-stroke. Nowadays very few two-stroke engine powered vehicles are in market, because they create higher pollution in comparison to four-stroke engines. Although the power output in two-stroke is more than four-stroke engine.
The working mechanism of a four-stroke motorcycle engine.
- The 1st stroke is suction in which piston moves downwards in the cylinder and sucks the mixture of air and fuel.
- The 2nd stroke is compression here the air-fuel mixture is compressed as piston comes upward. At the end of this cycle, spark plug generates a spark inside the cylinder and hence combustion starts.
- Here comes the 3rd power stroke as fuel burns inside the cylinder it applies huge amount of force on piston and pushes it downward. the energy generated in this stroke is stored via flywheel which absorbs the sudden jerk impact on cylinder and absorbs the energy for the next three strokes.
(flywheels are generally round-shaped heavy iron wheel which is directly connected to a crankshaft. it absorbs the energy in the form of inertia and maintains the smoothness of the engine. there are many other factors which needs to be taken care for smooth function and balancing of the engine.)
4. The last one is exhaust in this piston moves upward and releases the burnt gasses to the exhaust cylinder and from there it is released to the environment.
(exhaust cylinder reduces the intoxicates of released gasses and also cancels the noise created by engine.)
As the pistons move up and down, they turn a crankshaft, which transforms the energy from the pistons into rotary motion. The rotational force of the crankshaft is transmitted, via the transmission, to the rear wheel of the motorcycle.
Types of a motorcycle engine.
Motorcycle engines are classified on the basis of three characteristics:
- The no. of cylinder,
- The capacity of combustion chamber i.e. volume in cubic centimeter(cc), and
- The number of strokes.
Note: –here all the engines are reciprocating internal combustion engine. Their constructions are same as of an i.c. engine
- Single-cylinder: The single-cylinder engines have one piston to produce power. In these four-stroke internal combustion engines, the piston reciprocates four times in a cycle to produces one power stroke. The strokes are 1. INTAKE, 2. COMPRESSION, 3. POWER STROKE and 4. EXHAUST. It is the commonly used engine at lower cost (modern) motorcycles.
Pros: simple in construction
- compact size,
- high torque at low revolutions.
- Cons: vibration is very high and thus
- difficult to balance.
E.g.- KTM Duke 200, 390, 690. Hero Splendor, Honda Dream Yuga etc.
2. Parallel-twin: Parallel-twin engines are similar to single-cylinder engines, but here two cylinders are used. As, both the cylinder’s piston moves up and down together, so they suffer from the same issues of vibration like a single one. However, because there are two pistons the power strokes are fringe at opposite times, hence the power output is even.
- Pros: simple design,
- easier to manufacture,
- low maintenance and more cost-effective than the Flat Twin or V-Twin engines.
- Cons: engines produce many vibrations in comparison to the V-Twin or Flat Twin engines.
E.g.- Royal Enfield, Kawasaki Versys 650.
3. Inline triple (three): This engine has three cylinders arranged in a straight line or plane as shown in the picture. It is the first balanced engine in inline series, the inline triple is balanced around the crankshaft. Thus, it is smoother than the first two of its type. Inline triple is shorter than inline-four, which makes it easier to fit into the compact space of a motorcycle.
- Pros: It has also discreet balance,
- high performance, and low vibration.
- Cons: Plane imbalance: – Though the vertical forces sum to zero,
- the moment forces do not sum to zero.
- Heavy crankshaft,
- rough power delivery, etc.
E.g.- Yamaha MT-09 Tracer, MV Augusta Dragster 800, etc.
4. Inline four: This engine is used in motorcycles as well as in low budget economic cars. As the name suggests it has four cylinders mounted in a straight line or parallel along crankcase. The firing order (power delivery strokes) of typical inline-four engine is 1-3-4-2. It’s simplicity and perfect balance make it more popular, but as the power and size of engine increase the vibration of the engine also rapidly increases.
E.g.- BMW HP4, BMW S1000 RR, Honda 400X, etc.
5. Straight six: Straight six is the first engine in the inline category to have perfect primary and secondary mechanical balance and is known for its legendary smoothness. This engine has six cylinders mounted in a straight line or parallels to the crankcase. It is mostly used in engines displacements ranging from 2-5 litres. Honda had used this engine in RC series of motorcycle for racing and Rolls Royce in its GHOST (silver) 7.4L engine before world war II.
E.g.– BMW K1600GTL, Honda Rune, Suzuki Bandit 650 etc.
V (Vee) motorcycle engine
V-twin: It is the most basic engine in V-layout categories. Both the pistons are arranged such that they make together V-shape. The V-twin engines have a good natural balance in comparison to parallel-twin but due to uneven firing order, it gets a “burbling” exhaust sound which makes it less stable at fast turnings. This engine has good power to size ratio and lightweight.
E.g- Harley Davidson Glide, Honda Shadow.
V4 engine: Concept wise the V4 engine is a combination of two V-twin engines. Off course it has four cylinders and the odd no. cylinders are placed together with one side and the even no. are on another side, except in Honda’s VRF1200 motorcycle, which has cylinder 1 and 4 in one side and 2,3 other. The engine has good power delivery (high performance) and good stability (low vibration), as its four pistons are generating power at regular intervals.
The engine is quite compact in comparison to inline-four, which makes it easier to fit in a motorcycle frame. The construction of this engine is complex and thus it is quite problematic to locate its parts.
E.g.- Aprilia RSV4 RF, Honda CTX 1300 Deluxe, Honda RC213V-S, etc.
3. V8 engine: A V8 engine is an eight-cylinder V-type engine. In this, the cylinders are mounted on the crankcase in two sets of four, with all eight pistons driving a common crankshaft. In another language, it is basically two parallel inline-four engines sharing a common crankshaft. Many racing bikes use the single plane crankshaft because it allows faster acceleration and more efficient exhaust system designs.
The most remarkable thing is that most of the V8s have used some complex cross-plane crankshaft with heavy counterweights to eliminate vibrations, as a result, these engines are smoother than V6 engines and less expensive than V12.
e.g.- Moto Guzzi V8, Drysdale 750 V8, PGM V8.
Flat twin: Flat twin is a two-cylinder I.C. engine with cylinders on the opposite sides of the crankshaft. These engines were used more than a century. They were used in motorcycles as well as in Automobiles, light aircraft and stationary power plants etc. flat-twin engines have the advantage of excellent air cooling and good balancing whereas it has limitations in degree of lean angle.
E.g.- BMW R 1200 RT, BMW R NineT, BMW R 1200 GS.
Flat four: Also known as “Horizontally opposed four” is a flat Boxer engine with four cylinders arranged in two horizontal sides just the double of ‘Flat twin’. These engines have the advantage of good balance of the reciprocating parts, a low centre of gravity and very short engine length. The layout also lends itself to efficient air cooling and excellent thermal balancing.
E.g.- Honda Gold Wing, Zundapp K800.
Flat six: Flat six engines are also known as horizontally opposed-six as here the six cylinders are arranged opposite to each other in two banks of three cylinders on each side of a central crankcase as in the figure. The pistons are mounted to the crankshaft such that opposing pistons move back and forth in opposite directions at the same time, somewhat like a boxing competitor punching their gloves together before a fight, which has led to it being referred to as a boxer engine.
The configuration results in an inherently good balance of the reciprocating parts, a low centre of gravity, and a very short engine length.
However, it is an intrinsically expensive design to manufacture, and somewhat too wide for compact automobile engine compartments, which makes it more suitable for luxury sports cars, cruising motorcycles, and aircraft.
Only a few automakers, including Porsche and Subaru, currently use horizontally opposed engines. Porsche continues to be the most prominent manufacturer of flat-6 engine luxury sports cars.