Clean spark plugs on your motorcycle

The spark plug generates a spark that ignites the gases pushing the piston, causing the crankshaft to rotate. The spark plug must perform its function in hellish conditions, and the first weak points are problems: difficulty in starting, poor engine performance, consumption and increased pollution. Inspection and replacement varies from every 6 km to 000 km, depending on the type of engine and its use.

1- Disassemble the candles

Depending on the architecture of your motorcycle, removing the spark plugs takes only a few minutes or requires tedious work: dismantling the fairing, air filter housing, removing the water radiator. In principle, the key for the spark plugs in the on-board kit is enough. If accessibility is difficult, buy a professional wrench (photo 1b) that matches the size of your base. In the vast majority of cases, it is 18 mm or 21 mm. On a motorcycle with spark plug wells facing the road, blow compressed air through the gas station to remove dirt (especially chips) before dismantling. Otherwise, they can interfere with the entry of the key or - catastrophically - fall into the combustion chamber after the spark plug is removed.

2- Inspect the electrodes

When you look at a spark plug, what really matters is the condition of its electrodes. The ground electrode is connected to the base, the center electrode is isolated from the ground. High voltage current jumps between the electrodes and causes a series of sparks. The appearance and color of the electrodes, especially around the control box, provide information on the condition and settings of the engine. A candle in good condition has a small brown carbon deposit (photo 2 a). Overheating of the spark plug is indicated by very white electrodes or a burnt appearance (photo 2b below). This overheating is usually due to improper carburation that is too poor. The spark plug can be clogged with soot (photo 3c below), which leaves marks on your fingers: improper carburation (too rich) or clogged air filter. Greasy electrodes reveal excessive oil consumption of a worn out engine (photo 3g below). If the electrodes are very dirty, too far apart, corroded by electrical erosion, the spark plug must be replaced. The manufacturer's recommendation for replacement spark plugs ranges from every 6 km for an air-cooled single-cylinder engine to 000 km for a liquid-cooled multi-cylinder engine.

3- Clean and adjust

The spark plug brush (photo 3a below) is used to clean the base threads. The electrodes should be brushed so that the plug is pointing downwards (photo 3b opposite) so that the loose residue does not fall into the plug, but out of it. Some candle manufacturers prohibit brushing as this can damage the protective alloy covering them as well as the insulating ceramics. Wear leads to an increase in the interelectrode gap. It becomes more and more difficult for the spark to jump correctly. In this case, the start of combustion is poor, resulting in a small loss of power and an increase in consumption. The distance is indicated by the manufacturer (example: 0,70 mm). Take the set of wedges. The 0,70 gasket should slide accurately without effort (photo 3b below). To tighten, gently tap the protruding ground electrode (photo 3g below). Wipe the outside of the white porcelain with a rag.

4- Tighten with precision

For a long time, two theories coexisted: reassembling a spark plug with clean and dry threads, or, conversely, with threads coated with a special high-temperature grease. Your choice. The most important thing is to carefully hook the candle on its first thread, without making any effort, if possible, directly by hand. A beveled spark plug immediately resists, risking "screwing up" the threads on the cylinder head if force is applied. Normal human strength should only be used at the end to tighten. Bring the new spark plug into firm contact with its mating surface, then turn another 1/2 to 3/4 turn. For an already installed spark plug, tighten it 1/8–1/12 of a turn (photo 4 a). The difference between new and already installed is that its seal is broken.

5- understand the heat index

The candle, by its structure, is designed to work at the desired temperature, called "self-cleaning". The operating temperature range is from 450 ° C to 870 ° C. Thus, combustion residues burn, trying to settle on the spark plug. Below the spark plug becomes dirty, from above, ignition can occur by itself, without a spark, due to heat. The engine starts to rattle when accelerating. If this is not taken into account, the piston can be damaged by heat. The cold spark plug dissipates heat quickly, which contributes to an active engine and sporty driving. A hot spark plug slowly dissipates heat to warm up enough on quiet engines to prevent clogging. It is a heat index that calibrates candles from hot to cold. This must be observed according to the manufacturer's recommendations when purchasing candles.

Difficult level: easily

Equipment

– New spark plugs according to the manufacturer's recommendations (dimensions and thermal index for each engine type).

- Candle brush, rag.

- Set of washers.

– A spark plug wrench from the on-board kit or a more complex wrench when access is difficult.

Not to do

- Trust some manufacturers' marketing that suggests that their spark plugs increase engine power, reduce fuel consumption, reduce pollution. Any new spark plug (of the right type) will improve the performance of an outdated spark plug. On the other hand, some plugs are more expensive because they are much more resistant to wear (they last much longer without losing power).