Spark plug observations

[Craig380]

When I got my used 650K6 from the dealer, they gave it a full service, including new, standard NGK plugs. After about 6,000 miles (mostly brisk open-road riding, almost no town work) I replaced them with a set of Iridiums.

The standard plugs were pretty much unworn, gap was about 30thou / 0.75mm.

During the week I thought I'd have a look at the Iridiums as they'd done 8,500 miles of the same type of riding. Again, zero electrode wear and no sign of wear elsewhere, gap was still bang on the 0.7mm which I'd set them at.

So the moral of the story is: SV650s seem to give their spark plugs an easy life.

[Red ones]

Mine get replaced at 20,000 miles

[R1ffR4ff]

I tried a set of Iridiums in my Curvy and they seemed a little flat in response and ran a little lean.I could have adjust the fuel mix but couldn't bothered so stuck the supplied Denso plugs back and all good again.

YMMV

HTH :)

[SV650rules]

When I got my used 650K6 from the dealer, they gave it a full service, including new, standard NGK plugs. After about 6,000 miles (mostly brisk open-road riding, almost no town work) I replaced them with a set of Iridiums.

The standard plugs were pretty much unworn, gap was about 30thou / 0.75mm.

During the week I thought I'd have a look at the Iridiums as they'd done 8,500 miles of the same type of riding. Again, zero electrode wear and no sign of wear elsewhere, gap was still bang on the 0.7mm which I'd set them at.

So the moral of the story is: SV650s seem to give their spark plugs an easy life.

Normally iridium plugs will last 70 to 75,000 miles in a car (or over 120,000 if you believe what you read in American Forums :rolleyes: ), so motorbikes definitely harder on plugs than a car. The iridium tip resists the heat and spark erosion much better and are supposed to 'focus' the spark better due to smaller diameter of the tip, my wifes Honda Jazz uses 'double iridium' plugs where both the centre and ground electrodes are iridium as opposed to just centre electrode on most plugs, but they are pricey :(

[Bibio]

with spark plugs its not just the tips that erode. spark plugs can look fine but the resistance breaks down, which is the biggest cause of spark plug failure.

[Craig380]

with spark plugs its not just the tips that erode. spark plugs can look fine but the resistance breaks down, which is the biggest cause of spark plug failure.

Yes, although I've never had a spark plug resistor fail as yet ... however I have had resistors in the plug caps fail.

On my old GT380 I used to use platinum plugs (later replaced with Iridiums) and non-resistor caps, and they never, ever needed re-gapping or cleaning. Used to give the tired old ignition system a helping hand :)

[SV650rules]

Yes, although I've never had a spark plug resistor fail as yet ... however I have had resistors in the plug caps fail.

On my old GT380 I used to use platinum plugs (later replaced with Iridiums) and non-resistor caps, and they never, ever needed re-gapping or cleaning. Used to give the tired old ignition system a helping hand :)

I have never had an integral spark plug resistor fail either (on NGK there is an 'R' in the plug number for resistor), the gap is the main thing, because as that gets bigger the coil has to produce more voltage to jump the gap and very often the higher voltage can make a coil insulation break over internally and fail. Iridium and platinum plugs need less voltage anyway because finer tip makes it easier to produce a spark and give everything in ignition circuit an easier life.

[R1ffR4ff]

https://www.bikesmedia.in/reviews/difference-between-iridium-spark-plugs-and-normal-copper-spark-plugs.html

[SV650rules]

https://www.bikesmedia.in/reviews/difference-between-iridium-spark-plugs-and-normal-copper-spark-plugs.html

The guy who wrote the article is a bit suspect on electrical knowledge, he states that iridium has higher electrical resistance than copper and will degrade performance, the spark is high voltage low current, so a few extra ohms is neither here or there. Copper core is used for cooling / good heat transfer away from tip into body of plug, not electrical conductivity, otherwise why would plug maker fit a resistor into plug body - iridium plugs still have copper alloy core with iridium tip laser welded onto end to resist spark erosion.

[R1ffR4ff]

The guy who wrote the article is a bit suspect on electrical knowledge, he states that iridium has higher electrical resistance than copper and will degrade performance, the spark is high voltage low current, so a few extra ohms is neither here or there. Copper core is used for cooling / good heat transfer away from tip into body of plug, not electrical conductivity, otherwise why would plug maker fit a resistor into plug body - iridium plugs still have copper alloy core with iridium tip laser welded onto end to resist spark erosion.

Yes but in your previous post you made a point of saying that the lower resistance of Iridium would be beneficial which is fact incorrect as Iridium has a higher resistance.

Also resistors are fitted to Spark plugs to suppress Back EMF from interfering with the ignition circuit.

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[Craig380]

Iridium isn't as good an electrical conductor as copper, it's true. But because it's a much harder metal, the electrode tips can be made much narrower and more pointy (pointy, geddit ;)) than with a conventional copper-cored iron-tipped plug.

This lowers the actual voltage required for the spark to jump the plug gap, which means for a given HT voltage from the coils you get a more reliable spark in marginal conditions (such as in a old 70s 2-stroke with an over-rich, oily fuel mixture, or in a high-output turbo engine, in which high boost pressures can literally blow the spark out).

As pointed out above, rare-earth plugs will also wear less. But as I said in my original post, conventional plugs don't wear much at all in SVs either. You pays your money ... although the price gap for a pair of Iridiums isn't that much more than a pair of ordinary plugs these days.

[SV650rules]

Yes but in your previous post you made a point of saying that the lower resistance of Iridium would be beneficial which is fact incorrect as Iridium has a higher resistance.

Also resistors are fitted to Spark plugs to suppress Back EMF from interfering with the ignition circuit.



As costs have come down Iridium plugs have been fitted by most car makers for a few years now, both our Honda cars came with them as standard.

I never said Iridium had lower resistance than copper alloy, what I said was that due to the small diameter (made possible by heat resistance and hardness of Iridium) an Iridium tip needs lower voltage to form a good spark. Due to the fact that spark voltage is over 20KV and very low current a piddling little extra fraction of an Ohm in the circuit caused by bulk resistance of Iridium slug is neither here nor there, to put it in perspective the integral suppressor resistor in plug body is 5000 ohms.

http://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/when-should-i-use-a-resistor-spark-plug

[R1ffR4ff]

It only needs 7kV to jump the gap on a Spark plug.

The 2017 SV650s come with NGK MR8E-9 Platinum plugs.

https://ultimatemotorcycling.com/2016/05/18/2017-suzuki-sv650-review-12-fast-facts/



Also I like to take my plugs out and check them from time-to-time as they give a good indication of how the engine/mixture is running but it's easier for me to get to my front plug on a,"Naked" and especially as I've removed the horn bracket and only have to remove the three Rad bolts and push the Rad forward.

At the end of the day it's down to what the user finds runs best for their machine.My 1999 curvy runs better on standard copper Plugs.

HTH :)

[Red ones]

It only needs 7kV to jump the gap on a Spark plug.





The gap should be 0.7mm which at 30kV/cm for discharge is actually 2.1kV for spark.

[R1ffR4ff]

The gap should be 0.7mm which at 30kV/cm for discharge is actually 2.1kV for spark.

Cool :)

[glang]

Hi, Ive always worried with running plugs for very high milages about the risk that the ceramic around the electrode might break up. It is subjected to high temperatures plus more importantly thermal cycling and of course if it fails could cause a lot of damage....

[R1ffR4ff]

Hi, Ive always worried with running plugs for very high milages about the risk that the ceramic around the electrode might break up. It is subjected to high temperatures plus more importantly thermal cycling and of course if it fails could cause a lot of damage....

My concern with plugs that may not be touched for a long while and having been through it,is welding to the cylinder head.

Sometimes it's an advantage to have to make regular service checks and break the seal on Spark plugs I've found.

This is the same reason I'm happy with Standard coolant and renew it at least every two years as I then flush my cooling systems before putting fresh coolant in.

My 10 penn'th.

[SV650rules]

Long life Iridium and platinum plugs have a special tri-valent nickel plating on threads which is designed to resist sticking to aluminium of the head, it is much superior to passivated zinc or cadmium plating of normal life plugs. I changed the OEM fitted Iridium plugs in my Honda Civic last year at 70,000 miles and they unscrewed very easily (in fact much easier than normal plugs I have changed at as little as 7,000 miles). Also changed plugs in wifes Jazz at 65,000 and they came out easily. Modern ceramics are leaps ahead of older ceramics as well in terms of heat resistance and breaking up.

The difference between a spark jumping a gap in free air at normal pressure and doing the same at higher pressure and heat of the combustion chamber (where mixture can swirl and try to 'blow out' the spark ) also has to be taken into account. But the end result is that finer tip of Iridium (or even better Platinum) plugs can focus and stabilise the spark. Some plugs with multiple ground electrodes (Bosch seem to favour these but warn against using them in Japanese engines) work on the fact that electricity will always take shortest path and when one gap has opened up due to erosion of the side of one ground electrode and ground electrode opposite the spark will go to next ground electrode and a fresh place on side of centre electrode and ignore the largest gap, thus offering 4 erosion points instead of 1.

The spark actually happens when power is removed from ignition coil and the magnetic field collapses, because the discharge path of primary coil (higher current low voltage coil, few turns of heavier gauge wire) is electrically blocked (by open points or a transistor that is turned off = non conducting state) the voltage in secondary coil (high voltage with many turns of smaller gauge wire) will rise until it is high enough to discharge its energy somewhere (across the spark plug gap hopefully) if the gap is larger than it should be the voltage will rise until it can jump the gap, if the gap is too big this voltage can rise high enough to break over the coil electrical insulation and once that happens the coil often fails. So the time power is applied to the coil (called 'dwell time' actually charges the magnetic field, and when power is removed from primary coil the energy stored as a magnetic field will create a spark on the secondary coil side).

interesting article here http://bustekhub.com/index.php/2016/08/16/spark-plugs-101/

[Craig380]

A quick update to this: another 7,000 fastish open-road miles later, I thought I'd check the Iridium plugs again. They were in perfect nick, and the gaps had not changed. So basically, if you've got a K3 to K6 pointy, unless you start getting a misfire, Iridium plugs hardly ever need checking :)

[Bibio]

you only check plugs if your having problems.
you only change plugs as per manufacturer recommendation or your having problems.

dont keep checking modern plugs especially thin walled ones like the SV has. you will crush the sealing washer too much and put more stress on the threads.