Combined spark plug caps and coils – What are they?

Motorcycle ignition (spark) systems have changed massively over the years from the early magneto/distributor mechanical type systems found on older 60’s and 70’s (and earlier) bikes, to the separate ignition coils found on many 80’s and 90’s bikes to the combined spark plug/coils (also called ‘coil on plug’ systems) found on modern bikes (first used in the mid to late 1990’s).

Basically, all the above systems (roughly) do the same job of enabling the spark plug to spark and fire at the correct time (More info can be found in these good articles here and here)

Combined spark plug coils and caps found on modern motorcycles (the caps above are from a 2002 Yamaha YZF-R1)

Older style separate coil and cap (these are still used on some bikes and scooters)

The difference between the 2 spark plug systems pictured above are the combined plug/coil (top pic) has the ignition coil built into the plug cap, the older style coil (bottom pic) uses a separate cap and spark plug coil connected by a length of heavily insulated HV (high voltage) wiring.

Top and bottom of the combined coil/cap showing the spark plug hole and the electrical connector block

Separate spark plug cap

Apart from the benefits of being a newer design, combined spark plug and coil systems have several benefits over separate coil/plug set ups:

• Less parts so more they SHOULD be more reliable as there’s less wires and parts to get damaged during running and installing/removing.
• No external wiring so less chance of water or dirt getting into the system and causing faults.
• Shorter distance between the coil and the spark plug which should make the ignition sequence very slightly faster.
• Cheaper to replace. Most separate coil packs usually operate between 2 and 4 cylinders/plugs each, which makes the cost of replacing them more expensive then combined plugs which only cover 1 cylinder/plug if they fail.
• Space saving. Modern bikes often don’t have much room under the bodywork and combined cap/coils use alot less space then the older style, seperate coil, wire and cap.

Combined plug coils and caps mounted into the top of a Yamaha YZF-R1 engine.

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