Spark plugs for scooters Vespa, Lambretta & Co.
My personal spark plug universe is quite small and simple:
- Original engines: BOSCH W5CC
- Light tuning: BOSCH W4CC
- Ambitious tuning: BOSCH W3CC
- and sometimes also: BOSCH W2CC
That's how it's always been for me and unfortunately it can't stay that way, because my universe has been crumbling for a while! BOSCH - spark plugs have been unavailable for some time. Exception: We were still able to secure a large stock of
BOSCH W3CC. But that's no reason for my world to fall apart, because of course we have great alternatives. They just have different names and lower value is hot instead of cold... Reason enough to take a look at the topic of spark plugs. At our Scooter Center Store you get
spark plugs from the leading manufacturers.
Spark plug thread
Spark plugs are screwed into the spark plug thread of the cylinder head. They come in various diameters and lengths. The usual threads are M10, M12 and M14. Classic Vespa and Lambretta vehicles have an M14 thread. Modern engines, four-strokes 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 specifications. 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 cause loss of performance, if the engine starts at all. Due to unclean combustion, deposits would quickly form in the combustion chamber, which can cause engine damage.
Heat rating
The heat rating is crucial for the thermal durability of the spark plug and its self-cleaning effect. A distinction is therefore made between so-called cold and hot spark plugs. A cold plug is for engines that develop a very high combustion chamber temperature, usually these are engines that, relative to their displacement, have a lot of power. A hot plug, on the other hand, is used in lightly loaded production engines. This type of plug quickly reaches a high temperature, which burns off the soot on the plug well. The temperature resistance is achieved by differently designed insulators. A cold plug can dissipate a lot of heat via the cylinder head, in a hot plug this is exactly what is strongly prevented. The heat rating has nothing to do with the strength or performance of a spark plug. A cold plug 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 will glow and severely damage it. The heat rating of a spark plug is not standardized. Each manufacturer has its own code.
- 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 of the precious metals, the spark plugs are accordingly more expensive than the copper counterparts. The material is ultimately of interest only for wear, only the extremely thin iridium electrodes (Ø=0.6mm) have a higher ignition voltage, improving the propagation of the flame front in the combustion chamber.
Caution is the mother of the ceramic plug!
The insulator head of the spark plug is made of ceramic. Of course, you shouldn't work here with brute force. Spark plugs should be handled carefully and better not be dropped, they should also be protected from moisture. Use a
spark plug wrench with rubber insert.
What is the tightening torque of a spark plug?
If it is chosen
too low, there is a risk of compression loss and overheating. Breakage of insulator or center electrode due to vibrations is also possible. If the
torque is too high, it can lead to the spark plug breaking off. The housing can also expand or twist. The heat dissipation zones are disturbed, overheating and melting of the electrodes up to engine damage are imminent. The manufacturers recommend a
proper installation of a spark plug using a
torque wrench. Since we know that hardly anyone does this and it doesn't even fit, for example, on the Lambretta, you could follow this rule of thumb: Hand-tight = screw in by hand and then tighten another quarter to half turn with the spark plug wrench. Our new bgm spark plug wrench: protects the spark plug and with magnet so you don't burn your fingers when removing the plug.
TIP: You can clean spark plugs during installation and removal with a fine
wire brush.Spark plug image
Based on a
plug image you can also draw conclusions about proper combustion of your engine.
PERFECT: If the plug is "fawn brown" your engine is burning perfectly.
LEAN: If the plug is too light - white, then it gets too hot, possibly the carburetor is too lean or the ignition is incorrectly set.
RICH: If you have a black, sooty spark plug, then the engine is running too rich.
Spark plug connector
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 connector costs only a few euros, which are well invested. TIP: I always have a second connector including spark plug cable in my tool kit.
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