Yamaha TP-7023 User Manual download pdf (Page 4)

SPARK PLUG DESIGN

Every year the range of NGK spark plugs grows to

accommodate the ever increasing demands of modern engines.

Spark plug design must take into consideration many features

of an engine including physical dimensions, combustion

chamber shape, cooling abilities, fuel and ignition systems.

Spark plugs play a vital role in producing the maximum power

from an engine whilst keeping fuel consumption and emissions

to a minimum. Choosing the correct spark plug type will help a

vehicle manufacturer meet legislated emission targets and

assists the motorist in getting the best from their engine.

Increases in the size and the requirement to improve the

cooling of the inlet and exhaust valves have meant that the

space available for the spark plug is severely restricted on some

cylinder heads. A change in spark plug design, possibly the

adoption of a taper seat and extended reach (threaded portion)

or even the use of a smaller diameter is often the answer. Some

engines require the use of two spark plugs per cylinder and

again due to space restrictions these might be of different sizes.

Changes in fuelling systems and the fuel itself have meant some

special features being adopted at the ‘firing end’ of the spark

plug. Extra projected types push the spark position into the

heart of the combustion chamber to promote better combustion

of the fuel/air mixture, which is weaker than ever in an effort to

improve economy. Modern engine manufacturers often require

increased spark gaps to allow a longer spark duration, which

again aids more efficient combustion.

BKR6EK

IZFR6B

BPR5ES-13

BKR6EQUPBCP6ET

ZFR6E-11

HEAT RANGE AND HEAT DISSIPATION

Spark plugs do not produce heat in the combustion chamber.

One of the functions of the spark plug is to dissipate some of

the heat produced during combustion. This is mostly transferred

into the cylinder head. The 'Heat Range' indicates the measure

of the spark plug's ability to do this. A 'hot' spark plug is

designed to maintain a sufficiently high temperature at the

insulator nose to burn off carbon and oil deposits. A 'cold' spark

plug is designed to allow a faster transfer of heat to the cylinder

head thus preventing overheating and premature failure.

The heat range selection is obviously a complex task with

many factors to take into account. NGK engineers therefore

make specific recommendations for each engine and the use

to which it is put.

HOT TYPE

eg BR4ES

COLD TYPE

eg BR10ES

To combat the ‘cold fouling’ effect that can occur in some engines using unleaded fuels specially arranged

ground electrodes are sometimes used. These can force the spark to discharge across the insulator and thus

burn away any built up carbon that could cause poor starting or misfires. It is not uncommon to find two, three

or four ground electrode arrangements in new vehicles. The use of precious metals on the tips of the spark

plug electrodes is not uncommon especially on higher performance engines. Whilst these spark plugs do have

increased service life they are often specified because of their superior ignition qualities.

Our engineering departments work very closely with the engine and vehicle manufacturers to produce the ideal

spark plug type for each application. Any change in production is expensive for a manufacturer and therefore

new spark plug types are only produced where necessary. NGK employ the very latest production technology

to ensure that every aspect is catered for – performance, economy and value.

Wide gap Twin ground

Three ground Four ground

Extra projected

and shielded

Precious metal

1 2 3 4 5 6 7 8 9 ... 107 108

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Yamaha TP-7023 User Manual Page 4

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