Spark plugs for scooters Vespa, Lambretta & Co.
My personal spark plug universe is quite small and simple:
- Original engines: BOSCH W5CC
- Easy tuning: BOSCH W4CC
- Ambitious tuning: BOSCH W3CC
- and sometimes also: BOSCH W2CC
It has always been like that for me and unfortunately it can't stay that way, because my universe has been crumbling for a long time! BOSCH spark plugs have not been around for a long time. Exception: We were able to get a large stock of BOSCH W3CC to back up. But no reason that the world should collapse for me, because of course we have great alternatives. But they are called different and a lower value is warm instead of cold ... Reason enough to take a look at the topic of spark plugs.
With us in Scooter Center Shop you get spark of the leading manufacturers.
Spark plug thread
Spark plugs are screwed into the spark plug thread of the cylinder head. are available in different diameters and lengths. The usual threads are M10, M12 and M14. Classic Vespa and Lambretta vehicles have an M14 thread.
Modern engines, four-stroke and newer two-stroke engines with injection use the smaller plugs with M10 or M12.
The common thread lengths are 19mm (long thread) and 12,7mm (short thread). You should pay attention to the correct length of the spark plug and follow the manufacturer's instructions. A spark plug that is too long can damage the piston because it protrudes too far into the combustion chamber; a spark plug that is too short will certainly have a loss of power if the engine starts at all. Unclean combustion would quickly build up residues in the combustion chamber, which could damage the engine.
Heat value
The heat value is decisive for the thermal fatigue strength of the spark plug and its self-cleaning effect. A distinction is therefore made between so-called cold and hot spark plugs.
A cold candle is for engines that develop a very high combustion chamber temperature, usually these are engines that have a lot of power measured by their cubic capacity. A hot candle, on the other hand, is used in lightly loaded series engines. This type of candle quickly reaches a high temperature, which means that the soot that accumulates on the candle burns away well.
The temperature resistance is achieved through differently designed insulators. A cold candle can give off a lot of temperature through the cylinder head, with a cold candle this is exactly what is prevented. The calorific value has nothing to do with the strength or performance of a spark plug. A cold candle in a cold (weak) engine becomes oily or sooty and can break without damaging the engine itself. A hot spark plug in a racing engine burns up and damages it, usually severely.
The heat value of a spark plug is not standardized. Each manufacturer has its own code here.
- NGK from cold to hot = 10-9-8-7-6
- Bosch from cold to hot = 2-3-4-5-6
- DENSO from cold to hot = 37-34-31-27-24-22-20-16-14
Noble noble, the electrode material
Copper, platinum, silver or even iridium are used here.
The most common is copper, followed by silver and platinum. Due to the high prices for the precious metals, the spark plugs are correspondingly more expensive than their copper counterparts.
Ultimately, the material is only of interest for wear and tear, only the extremely thin iridium electrodes (Ø = 0,6mm) have a higher ignition voltage, and the spread of the flame front in the combustion chamber is improved.
Caution is the mother of the ceramic candle!
The spark plug's insulator head is made of ceramic. It goes without saying that brute force shouldn't be used here. Spark plugs should be handled with care and, better still, not be dropped, and they should also be protected from moisture. Use one spark plug wrench with rubber insert.
What is the tightening torque of a spark plug?
Is it too low selected, there is a risk of compression loss and overheating. A break in the insulator or center electrode as a result of vibrations is also conceivable.
Will that be Selected torque too high, the spark plug may tear off. The housing can also stretch or twist. The heat dissipation zones are disturbed, there is a risk of overheating and melting of the electrodes or even damage to the engine.
Manufacturers recommend for that professional assembly a spark plug torque wrench. Since we know that hardly anyone does that and that it doesn't work at all with the Lambretta, for example, you could follow the following rule of thumb:
Hand-tight = screw in by hand and then tighten a quarter to half turn with the candle wrench.
Our new bgm spark plug wrench: protects the spark plug and has a magnet so that you don't burn your fingers when removing the plug.
TIPP:
You can install and remove spark plugs with a fine one wire brush reinigen.
Spark plug picture
Using one Candle image you can also draw conclusions about correct combustion of your engine.
PERFECT: If the candle is "fawn" your engine burns perfectly.
SKINNY: If the candle is too bright - white, it will be too hot, the carburettor may be too lean or the ignition set incorrectly.
FAT: If you have a black, sooty spark plug, the engine is running too rich.
spark plug
With a spark plug connector, you should pay attention to whether it is used with or without a spark plug nipple / SAE nut. A spark plug connector is also a part that is exposed to heat and vibrations and should be checked regularly and replaced if necessary.
A good spark plug only costs a few euros, which is a pleasure to invest.
TIP: I always have a second plug and ignition cable in my tool.
