NGK

 

 

BR8
NGK B8ECS

£40.68 for 8 plugs including vat and delivery

 
NGK B7ECS
£40.68 for 8 plugs including vat and delivery

 

Spark Plug information

Firing end appearances

The appearance of the firing-end of a used spark plug graphically reflects the condition of an engine, the suitability of the spark plug heat range, and whether or not the fuelling and ignition systems are correctly set.

Normal condition

An engines condition can be judged by the spark plugs firing end appearance. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug is functioning correctly.

 

Deposits

The accumulation of deposits on the firing end is influenced by oil leakage, fuel quality and the engines operating period. Deposits come from:
Fuel: C (carbon), Pb (lead), Br (bromine)
Lubricating oil: C, CA (calcium), S (sulphur), Ba (barium), Zn (zinc)
Others: Fe (iron), Si (silicon), Al (aluminium), etc.

 

Dry and wet fouling

Although there are many different causes, if the insulation resistance between the center electrode and the shell is over 10M ohms, the engine can be started normally.

If the insulation resistance drops to 0, the firing end is fouled by either wet or dry carbon.

 

Lead fouling

Lead fouling usually appears as yellowish brown deposits on the insulator nose and this cannot be detected by a resistance tester at room temperature. Lead compounds combine at different temperatures; those formed at 370 420 degrees Celsius having the greatest influence on the resistance.

Overheating

After having overheated, the insulator tip is glazed or glossy, and deposits which have accumulated on the insulator tip have melted. Sometimes these deposits have blistered on the insulators tip.

 

Breakage

Breakage is usually caused by thermal shock due to sudden heating or cooling.

 

 

Normal life

A worn spark plug not only wastes fuel but also strains the whole ignition system because the expanded gap requires higher voltages. Worn spark plugs also reduce the engines efficiency, resulting in reduced fuel economy and increased exhaust emissions. The normal rate of gap growth is about 0.01 0.02mm/1,000 Km for four stroke engines and about 0.02 0.04mm/1,000 Km for two stroke engines.

 

Erosion, Corrosion, Oxidation

The material of the electrodes has oxidized, and when the oxidation is heavy it will be green on the surface. The surfaces of the electrodes are also fretted and rough.

 

Abnormal erosion

Abnormal electrode erosion is caused by the effects of corrosion, oxidation, reaction with lead, all resulting in abnormal gap growth.

 

Lead erosion

Lead erosion is caused by lead compounds in the gasoline which react chemically with the material of the electrodes ( nickel alloy) at high temperatures. Crystals of nickel alloy fall off because of the lead compounds permeating and separating the grain boundary of the nickel alloy. Typical lead erosion causes the surface of the ground electrode to become thinner, and the tip of the electrode looks as it it has been chipped.

 

Melting

Melting is caused by overheating. Mostly, the electrode surface is rather lustrous and uneven. The Melting point of nickel alloy is 1,200 1,300 degrees Celsius.

 

Pre-ignition range

Pre-ignition is a condition whereby combustion is initiated within the combustion chamber before the spark occurs at the plug. This results in uncontrolled ignition and combustion conditions.

If a spark plug operates at a temperature in excess of 1000 degrees Celsius for a prolonged period the electrodes can start to overheat. When excessively overheated, pre-ignition can occur, the electrodes and insulator tip may melt and piston damage may result.

Pre-ignition is usually caused by a temperature exceeding
850 degrees Celsius – 1000 degrees Celsius (1600 degrees Fahrenheit – 1800 degrees Fahrenheit)

Causes of overheating

  • Over-advanced ignition timing
  • Too lean fuel mixture
  • Excessive deposits accumulated in combustion chamber
  • Insufficient cooling
  • Insufficient spark plug tightening or failure to fit gasket
  • Too low octane gasoline
  • Too hot a spark plug fitted

Overheated

The plug has been subjected to a relatively heavy load and evidence of overheating can be seen in the oxidized electrodes and melted deposits which have formed on the insulator surface.

Recommendation
Check for over-advanced ignition timing and too lean fuel mixture. Check spark plug tightening and gasket. If conditions recur, use plug one step colder in heat range.

Melted

Overheated plug with melted electrodes and blistered ceramic insulator surface.

Recommendation
Check for over-advanced ignition timing and too lean fuel mixture. Check spark plug tightening and gasket. If conditions recur, use plug one step colder in heat range.

Worn Spark Plug

A worn spark plug not only wastes fuel but also loads the whole ignition system because the expanded gap requires higher voltage.

As a result, a worn spark plug may also cause engine damage and increased exhaust emissions.

Recommendation
Spark plugs should be replaced.

Deposits

The accumulation of deposits on the firing end is influenced by oil leakage, fuel quality and engine operating period.

Recommendation
Check for excessive amounts of lubricating oil entering into the combustion chamber. High quality oil should be used.

Spark plug tip temperature

     

Corona stain

A brown stain – often mistaken for gas leakage – is sometimes observed in a ring around where the insulator joins the metal shell of the spark plug. This discolouration is generally called Corona Stain and is the result of oil particles present in the air around the engine adhering to the insulator surface.

The Corona Stain is often seen on spark plugs that are installed deep into the engine such as on many four valves per cylinder engine applications. This is because oil particles are not blown away by air circulating around the engine compartment and thus adhere to the insulator surface. It is important to understand that Corona Stain causes no deterioration to the function of the spark plug.