The motorcycle spark plug: what it is used for and when and how it should be changed

Motorcycle spark plugs and ignition: how they are made, maintenance and replacement, useful tips.

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Motorcycle candle - Ph. Canva by bizoo_n

Spark plugs are the beating heart of our motorcycles, the spark that lights up the magic, but when it doesn't work, it makes us lose days of fun and health.

Here is a short guide on operation and maintenance to never remain on foot and to always have everything you need with you to turn on our bikes and our passion!

Content index

  1. What is a candle and how is it made
  2. Maintenance and wear
  3. Inspection and replacement
  4. Useful Tips

What is a candle and how is it made

The spark plug consists of a metal body, over which a steel rod (the central electrode) passes, isolated by a porcelain casing. At 0,5-0,7 mm from the tip there is another electrode, connected to the aforementioned metal body. The correct distance between the two electrodes is essential for the correct functioning of this device. As in cars with thermal engines, also in motorcycle the spark plugs are used to start the combustion process of the air-petrol mixture in the special chamber. This occurs through the production of a spark, which strikes between the two electrodes of the component.

Maintenance and wear

Like all components, the spark plugs are also subject to wear and must be checked and replaced in due time. Specific information relating to the number of kilometers traveled, after which a change is recommended, can be found in the booklet maintenance of the bike. On average these should be replaced every 30.000 km. Only spark plugs of the type recommended by the manufacturer or of a compatible model should be installed on the motorcycle. Also in this case it is useful to consult the above manual.

Let's consider a concrete example. DENSO Iridium Power Spark Plug 1 has a thread length of 19 mm, a width of 16 mm, a clamping of 22 mm, a diameter of 14 mm and a weight of 43 g. By virtue of its characteristics this candle is suitable for a large number of marche of motorcycles, such as: BMW, DAIHATSU, FIAT, FORD, HONDA, IVECO, MITSUBISHI, etc.

Inspection and replacement

A regular visual check of the spark plugs is useful in order to detect signs of malfunction:

  • The presence of carbon residues indicates a temperature of too low combustion or an excessively rich mixture.
  • If there are traces of oil on the electrodes, this could be a sign of a problem with the bands, probably worn, that they must be replaced.
  • If the ceramic shell has a white or beige, this could be a symptom of a too lean blend or that the candle is too hot.
  • A dark or blackish color can indicate a mixture oily or that the candle is too cold.

Useful Tips

Replacing spark plugs on a motorcycle is an operation that can be done independently. Before starting work it is clearly necessary to obtain a spark plug suitable for your motorcycle model and a spark plug wrench, often supplied when purchasing the vehicle. The maintenance booklet can also be consulted in this case to find precise information on the position of the accessory in the motorcycle.

The gearbox must be done strictly with the engine cold in order not to expose yourself to the risk of dangerous burns. First of all, the spark plug cap must be removed, exerting a slight force with your hand towards the outside of the spark plug tip. Once this is done, using the appropriate key, the candle will be removed. The new spark plug should preferably be screwed in by hand, trying not to exert excessive force.

For fixing it is advisable to use a dynamometric wrench, to tighten to the correct torque as indicated in the manufacturer's manual. After completing the tightening, as a last step you will put the pipette back on the spark plug. Using a few drops of engine oil as a lubricant can make it easier to screw the new spark plug into the threaded seat.