Motorcycle Engineering

Andrew Livesey

• Publisher: Routledge
• Year: 2021
• ISBN:
  9781000373387
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Aviation

Motorcycle Engineering is a primer and technical introduction for anyone interested in motorcycles, motorcycling, and the motorcycle industry. It provides insight into how motorcycles are made and operated.

Motorcycles, mopeds, and scooters are important factors in world transport, and they are playing an increasingly important role in transport policy as we move towards greater environmental awareness. Motorcycles and scooters give freedom of personal transport that enable large commuter distances to be covered quickly and easily. Their small footprint offers easy storage as only minimal space is required. To celebrate the importance of motorcycles on the world stage, a brief history is included with a detailed timeline detailing the development of the motorcycle alongside major world events.

Written in an accessible fashion, no previous knowledge of engineering or technology is required, as all technical terms are readily explained and a glossary and abbreviation list is included. Whether you are an enthusiast, racer, student, or industry professional, you will surely find this an enjoyable read and a handy reference book on your shelf.

Chapter 1

Power unit – engine

‘There ain't no substitute for cubes.’

Whether it's cubic inches or cubic centimeters, the more of them that you have in your engine, the more power you can develop. That's how it is for petrol and diesel engines – with electric motors, you need volts and amps.

Motorcycle sport is often grouped into engine sizes, so the competitor is challenged to get the most power out of the engine. There are also usually regulations on what is, and is not, allowed to improve the power output.

Tech Note

The term horsepower – HP – comes from steam engine sales agents of about 200 years ago saying how many horses their engines could replace. In French, this is cheval vapour (CV); in German, this is pferde starke (PS).

One HP, in any language, that is CV or PS, is equal to 33,000 foot-pounds per minute, that is 746 watts.

When we are talking about power output, we must be careful to compare like for like. When we say BHP (brake horsepower), we are talking about the engine power measured on an engine brake or dynamometer – dyno. But rolling road dynamometers measure power at the wheels – this is after the frictional losses in the transmission system – typically around 10% to 15%. Also, there are a number of different standards for measuring power outputs set by different organizations. The most popular are the American SAE standard and the German DIN standard. Both measure power but under different conditions, with variations like the use of air filters and the way that the cooling system is connected.

Power is about doing work in an amount of time – mathematically, it's work done per unit time.

Figure 1.1Kick start to get the engine going on a lightweight motorcycle.

IDENTIFICATION

Identification of the engine before working on it is very important. The VIN number will help identify the type, or classification, of the engine. The detail of the engine will be given in a separate engine number, the pre-fix will identify the engine type, and the serial number will identify the exact engine.

ENGINE PERFORMANCE

The two common terms used are:

• Power – this is work done in unit time.
• Torque – turning moment about a point.

Let's discuss them for clarity and then look at the calculations. When we are using the term power, we are referring to how much energy that the engine has. A big heavy motorcycle needs a big powerful engine. Power is about doing work in a time period; it means burning fuel in the time period. We can make a small four-cylinder engine – say one from a motorcycle like a Kawasaki ZX6R – produce over 100 BHP from its 600 cc, but we need it to rev at about 12,000 rpm.

For a mathematical definition of these terms, we need to start with work done. Work done is the amount of load carried multiplied by the distance travelled. The load is converted into force: for instance, the force needed to move the motorcycle in newtons (N). The distance is measured in meters. That is:

$$\text{Work done}\left(\text{Nm}\right)=\text{Force}\left(N\right)*\text{Distance}\left(m\right)$$

As we also express torque in Nm, it is common to use the term joule (J) for work done.

Tech Note

Joule is a term for energy. 1 J = 1 Nm

If we use a force of 10,000 N to take a drag-bike down a 200-m drag strip, then we have exerted 2,000,000 Nm, or 2,000,000 J. We'd say 2 mega joules (2 MJ). We'd need to get this amount of energy out of the fuel that we were using

The force is generated by the pressure of the burning gas on top of the piston multiplied by the area of the top of the piston. So, the work done is the mean (average) force of pushing the piston down the cylinder bore multiplied by the distance traveled.

Example

The work done during the power stoke of an engine where the stoke is 60mm and the mean force is 5kN

$$\begin{array}{lll}\text{Work Done}\hfill & =\hfill & \text{Force*Distance}\hfill \\ \hfill & =\hfill & 5\text{kN*}60\text{mm}\hfill \\ \hfill & =\hfill & 5000N\times 0.06m\hfill \\ \hfill & =\hfill & 300J\hfill \end{array}$$

Tech Note

The mathematical symbols used in this book are those found on your calculator or mobile phone:

• * is multiply and / is divide

The same mean force is going to create the torque. This time we are going to use the crankshaft throw – this is half the length of the stoke.

Example

Using the same engine

$$\begin{array}{lll}\text{Torque}\hfill & =\hfill & \text{Force}*\text{Radius}\hfill \\ \hfill & =\hfill & 5\text{kN}*30\text{mm}\hfill \\ \hfill & =\hfill & 5000N*0.03m\hfill \\ \hfill & =\hfill & 150\text{Nm}\hfill \end{array}$$

The work done by a torque for one revolution is the mean force multiplied by the circumference. The circumference is 2Πr so:

$$\text{WorkDone}=F*2\Pi r$$

$$\text{AsFr}=T$$

That is for one revolution. For any number of revolutions, where n is any number, the formula is:

Example

Using the same engine of the previous examples:

The work done in 1 minute at 6000 rpm will be:

Power is, as we said, work done in unit time, which is:

The motorcycle industry uses a number of different units and standards for power. From our calculations we can use watts (W) and kilowatts (kW) and then convert.

Tech Note

1 kW = 1000 W

1 watt = 1 J/second

1 kW = 1 kJ/s

Example

Following on from our engine in the previous calculations and examples:

$$\begin{array}{lll}\text{Power}\hfill & =\hfill & \text{Work}\text{Done}/\text{Time}\hfill \\ \hfill & =\hfill & 5657\text{kJ}/60\hfill \\ \hfill & =\hfill & 94.3\text{kW}\hfill \end{array}$$

The term horsepower (HP or hp) was derived by James Watt as the average power of a pit pony. These were small horses used to turn pulleys to draw water from Cornish tin mines (pits) before steam power became more popular. He equated the power of his steam engines to a number of these pit ponies. For our purposes 1 HP equals 33,000 ft-lb/minute.

In French horsepower is cheval vapour (CV); in German, it is pferde starke (PS).

For conversion purposes, 1 HP is equal to 746 W.

When talking about power and doing work, the weight of the bike comes into play. It's worth doing a comparison with performance motorcycles to get a good picture.

Terminology

One metric ton is 1000 kg. As a kilogram is equivalent to 2.25 pounds, a metric ton is the equivalent of an imperial ton – 2250 lb.

Table 1.1 Typical BHP per ton figures

Bike/car	Capacity	BHP	Weight (kg)	BHP per ton
Kawasaki ZX6R	599 cc	130	185	702
Harley Davidson	883 cc	53	263	201
Triumph Bonneville T120	1198 cc	80	224	357
Suzuki Hayabusa	1299 cc	173	251	689
Kawasaki H2 motorcycle	1000 cc supercharged	310	215	1442
Typical BTCC car	2-liter turbo	350	1000	350
German Touring Motorcycle - DTM	4-liter supercharged	500	112...